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Old 12-03-2004, 07:59 PM   #1
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Really rough running stang

1989 5.0 Mustang, completely stock. Car runs really rough from about 1100-1800 rpms. No idle hunting problems for the most part. Runs rough enough to make the car shake at highway speeds in fifth gear at speeds from 65-78mph. Does it on initial startup cold and also when warmed up(both open and closed loop mode). Has gotten progressively worse over the last year to the point it is almost not driveable. Oddly, the car idles fairly smooth and steady.

Ran diagnostic test and only codes given were for thermactor system. Egr works fine, no known air leaks, even blocked off all the vacuum lines to all accessories but no change in performance. Car runs fairly strong but has a speed range(rpm) where it runs like it's missing one cylinder. All spark plugs are medium gray with no oil fouling, they look normal. Plugs, cap, wires, rotor are new. TPS, Idle air bypass valve, TFI modle are new. MAF sensor has been cleaned and looked good too. Harmonic balancer was replaced too with no change in vibration. Tried pulling one plug wire at a time with engine running but could not detect a weak cylinder.

I have run out of things to try...............
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Old 12-03-2004, 11:24 PM   #2
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Run the KOER test then look for any codes.
My bet is on the EGR system, dist cap/rotor or wires.
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Old 12-04-2004, 07:11 AM   #3
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Quote:
Originally Posted by Bluegrass
Run the KOER test then look for any codes.
My bet is on the EGR system, dist cap/rotor or wires.
KOER test revealed thermactor system failure, that was it. No egr problems showed up. EGR has been removed, cleaned and inspected for free movement. You can visually see the diphragm does not move when racing engine up from under the hood.

Cap and rotor are perfect, the wires meet the same ohm resistance test that the old ones did and of course putting the new ones on changed nothing.

Gonna check coil resistance this morning, salt and pepper shakers and maybe run compression test. Any chance it could be a bad injector that would not show up on the diagnostic?
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Old 12-04-2004, 12:38 PM   #4
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You can't test the EGR operation in that way. It's not that simple.
It does not operate at any other time than in cruise driving with 'light throttle' as determined by the EEC.
When in cruise rpm range of about 1800 to 2400, with relitive steady throttle, the EEC detects this condition and opens the EVR valve allowing vacuum to the EGR at a 3 to 5 inch level to open the EGR. When the signal from the EEC closes the EVR valve, this valve must let air back into the EGR diaphram in order to allow it to displace the vacuum pulled to open the EGR.
If the EVR has a dirty filter air can't get back in very fast and holds the EGR open.
This will cause ragged running.
Good luck, keep digging.
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Old 12-06-2004, 04:02 PM   #5
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It runs rough in neutral or in gear at the same rpm's. Does the same thing with EGR blocked. Coil checked out ok too. Only codes given were 94 and 44. Car also has slight surging/bucking most noticeable when cold. Bucking is always present but light throttle stumble/surging is only noticeable when cold.

I'm bringing the car to somebody across the state on Friday that owns about 5 of every fox body part ever made. He says we will just start swapping parts till we figure out.

Any suggestions on which parts to play with?
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Old 12-20-2004, 01:00 PM   #6
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Ok, 2 wks ago I drive across the state and had a couple of hardcore Mustangers try to trouble shoot this beast and here's what we did:

Swapped fuel injectors, rail and pressure regulator with a known good running engine, swapped distributors with same engine, swapped MAF and MAP sensors, performed a cylinder balance test, inspected all vacuum lines, replaced coil, inspected 10 pin connectors, replaced two collapsed motor mounts. Also blocked off the pcv and checked for vacuum at the ventpipe to rule out a leaky intake manifold(internal leak).

End result, the car still has the same problem, it runs rough. WTF? At least my clutch chatter disappeared with the new mounts and the rough running engine doesn't shake the car quite as bad but it's still there.

Oh yeah, for kicks and giggles I ran a compression test out of desperation last weekend and all cylinders were within 10lbs of each other, 155-165. Plugs looked great. Car idles good, only gets the shakes under part throttle or high idle in the same 1200-1800 range. All other rpm's are smooth.

Still only shows 44 and 94 thermactor codes.

It's looking like the only thing that will fix this car is to replace it with an 05 model

Last edited by Goldduster360; 12-20-2004 at 01:16 PM.
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Old 12-20-2004, 02:55 PM   #7
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My hat is off to the effort made to find the problem.
Looking back over the posts, I see no sub of the EEC.
You might have to get deeper into the troubleshooting by doing things like putting a timing lite on and watching what happens to the timing.
Vacuum gage to see what happenes to the manifold vacuum.
Fuel pressure to see any level change.
There could be a wire harness problem.
Loose intake manifold bolts.
Set the idle up with the throttle set screw so the engine starts to run rough and go over as many things as possible for effects. Move cables, connectors etc.
I have taken an old dist cap and drilled a 5/8 hole at the base of #1 wire tower so I can see the rotor/ post relationship with a timing lite and how much shift there is with timing changes. If you try this you will see how much actual distance the spark has to jump in addition to the spark plug gap. Using a lite will freeze the image just like at the front damper location. If there is a large gap to fire accross, or the rotor won't stay relitivly still to observation relate it to the roughness if possible.
These are all extreme things to do but you have to keep getting deeper until you run onto some cause that can't be seen by the usual means.
Good luck.
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Old 12-20-2004, 03:31 PM   #8
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Thanx Blue, also EEC was subbed with an 89 GT spd, car did not improve so we swapped it back to my stock original. There were numerous other things done that day too but to no avail. This is the first time in 20+ yrs of car crafting that I have not been able to find and fix the problem.

Cars with carbs have about 5 things to troubleshoot, EFI seems to have an infinite combination of things that can go wrong.

My 78 Camaro isn't even a challenge to fix when something on it goes wrong, but this 5.0 computer stuff I don't know man.........
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Old 12-20-2004, 03:34 PM   #9
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Is there an online source(free) that shows all that wire colors and voltage that need to be present for the EEC wiring harness to work properly?
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Old 12-20-2004, 10:52 PM   #10
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I have a very similiar problem with a 94 GT I just bought. Keep us posted, as it might be the same problem I am having I'll do the same if I figure it out.

David
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Old 12-20-2004, 10:57 PM   #11
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if this is happening at little throttle then i would have to say it's a TPS. I know you already replaced it but that just sounds like the problem. I mean EGR makes sense to because EGR is only operated at part throttle conditions, but if you are showing no problems on a KOER test you probably aren't at the right conditions while just letting the car idle and it rev from the computer it may still not be the right operating conditions to see the problem. I would test your TPS just to be on the safe side. Even if you just got it alot of places have faulty brand new sensors occasionally. Hope you figure it out!! Drive ability problems with OBD 1 suck to find sometimes. One real thing that's nice with the mod motors to have the OBD 2
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Old 12-21-2004, 09:59 AM   #12
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Since the thermactor system pumps air into the heads under certain conditions such as warm up or extended idling, is it possible that this thermacotor malfunction(codes 44 and 94) could cause the o2 sensors to sense a false lean condition and cause the engine to run rich enough to miss a little under certain light throttle conditions? The thermactor would have to be diverting air to the heads when it is not required.

I will try unplugging the air hose going to the diverter valve and see if this does anything.

Also wondering if it's possible that faulty o2 sensors could be causing the thermactor error codes if they aren't able to properly relay fuel mixture values.
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Old 12-21-2004, 08:49 PM   #13
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I disconnected the air pump hose going into the diverter valve after I got home from a 40 mile drive this evening. Sitting in the driveway and revving up the engine the rough spot moved down in the rpm range to about 900 to 1100rpm. It ran noticeably smoother for a short time. Took it out for a drive and came back and the roughness seemed to return to about the way it was before. Maybe the computer is re-adapting to the lack of air being pumped to the heads and then the rougher running comes back?

When I unplugged the vacuum hose going to the diverter valve with the air pump hose off I could actually feel a suction through the open valve.
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Old 12-21-2004, 09:28 PM   #14
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Quote:
Originally Posted by Goldduster360
Since the thermactor system pumps air into the heads under certain conditions such as warm up or extended idling, is it possible that this thermacotor malfunction(codes 44 and 94) could cause the o2 sensors to sense a false lean condition and cause the engine to run rich enough to miss a little under certain light throttle conditions? The thermactor would have to be diverting air to the heads when it is not required.
Yes--I'm having sort of the same problem, I think. I'm getting a code 91/41 (oxygen sensor reads lean) when I scan for codes (KOER test) and I disconnected the vacuum hose from the diverter valve and plugged it and now I get a 94/44 code (AIR system inoperative, yep, cuz I disconnected it) but no 91/41 code.

I then plugged the vacuum hose back in to the diverter valve and then started and ran the engine for 5 minutes (it was already warm) and then unplugged it from the diverter valve and I felt a weak vacuum (compared to the vacuum I felt when I unplugged it after the KOER test) when I put my finger over it.

I don't think I should've felt any vacuum at all, so I think the TAD solenoid is bad and causing the AIR to divert upstream when it shouldn't, making the oxygen sensors read lean.
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Old 12-22-2004, 10:37 AM   #15
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Yeah Qaz, those are my thougts too. Do you know which path the air is suppossed to take when vaccuum is applied to the valve(cats or heads)?

My guess is the O2 sensors are getting lazy and maybe the thermactor failure just magnifies the problem.

My stang has 200,000 on the original O2 sensors but I have yet to get a failure code for them.
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Old 12-22-2004, 11:00 AM   #16
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Believe it or not, the Powertrain Control/Emissions Diagnosis manual doesn't say what path air is supposed to take when vacuum is applied! (Or if it does, I somehow missed it..)

But based on what I saw, and what one of the pinpoint tests in the PCED manual has you doing to troubleshoot a 91/41 code, it seems that air is supposed to go to the heads when vacuum is applied, and to the cat with no vacuum. I think the TAD solenoid is applying vacuum when it's not supposed to be, which is sending air to the heads, and making the oxygen sensors read lean.

When I disconnected the vacuum line from the TAD solenoid to the valve and plugged it and re-ran the self test (which is basically what that pinpoint test in the PCED said to do), it stopped giving me lean codes and started giving me thermactor failure codes.

That's because when it runs the self-test, it applies air to the heads and checks for a lean reading from the oxygen sensors. No lean reading is a thermactor failure.

A faulty oxygen sensor could cause the thermactor failure codes because of that.

I just ordered the replacement TAD/TAB solenoids, total $40 or so (from a discount Ford dealership, no parts stores have them). I'm replacing the TAB too because (1) if the TAD is bad, the TAB is probably gonna go bad too and that can cause backfiring while decelerating, from what I've heard and (2) it's only $20.
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Old 12-22-2004, 11:08 AM   #17
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Totally makes sense Qaz. If it's already dumping air into the heads the O2's won't sense a change in air input when the test calls for it giving the thermactor failure. Since my car did respond to removing the hose in a favorable way I know I have a thermactor failure. Since the car is not running smooth though I still suspect my O2's are spent too. Makes sense if the o2's aren't up to par you can't run an accurate diagnostic either. Sounds like I need to order those parts too and replace the o2's for good measure.

Thanx.

Also, does the manual list a special socket to get the o2 sensor out or is it just standard socket stuff?
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Old 12-22-2004, 12:00 PM   #18
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Bosch recommends a 60,000 mile replacement interval for the O2 sensors on the 87-93 Mustang, if that gives you an idea of just how spent your sensors might be. When you replace them, you might want to take an extra couple of minutes and check that the 12V heater voltage is there with the key on, too. (It'll be on the two white wires from the sensor).

On the Mustang, there is room to use either a 7/8" wrench or an oxygen sensor socket (which is a 7/8" socket with a slot down the side for the wires..about $10 at any autoparts store).

I used an oxygen sensor socket last time I replaced them. The Mustang is one of the EASIEST cars to change the oxygen sensors on.
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Old 12-22-2004, 02:00 PM   #19
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Thanx for the tips Qaz.

Last edited by Goldduster360; 12-22-2004 at 02:09 PM.
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Old 12-23-2004, 09:49 PM   #20
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Today I replaced all of the fuel injectors with a set of reconditioned (cleaned/flowed) 4-hole spray #19 injectors (a bit of an upgrade from the original pintle-spray ones) because two of 'em were leaking (from the top). I also replaced the fuel pressure regulator with a new one (non-adjustable GP Sorensen stock replacement from Autozone).

After I put it all back together, I took it for a test drive and when I got back home I did a KOER test.

Now it is giving me a code 45 which means "Thermactor Air System is always upstream during KOER test"...which is exactly what I suspected to be the problem..except before I replaced the fuel injectors and the fuel pressure regulator, it was giving me those lean codes 41/91.

Before I replaced the fuel injectors, I ran a cylinder balance test and the computer gave me a code 9 when it was done indicating that it didn't detect any weak cylinders.

But I guess these old injectors were enough out of balance that the computer couldn't accurately test the thermactor air system. Also, when I last replaced the plugs some cylinders looked like they were running rich and some looked like they were running lean, which I suspected was due to the injectors being out of balance. Basically, some are more clogged than others. If they're all clogged an equal amount, the computer can compensate. When they're clogged unequally(more likely), the computer cannot compensate, and so you get lean and rich cylinders.

Goldduster 360, did you run a cylinder balance test? I saw that you tried disconnecting the spark plug wires, but there's a built in test in the computer that can be accessed as follows:

1)Do a KOER test.

2)Within 2 minutes after the last code is output, lightly press the gas pedal

3)The computer will kill each cylinder in turn and detect the RPM drop. You'll see this on the tach and you'll notice it running a little rougher

4)When it's done, it'll output a code. If it detects a weak cylinder, it'll output a code 1 through 8 corresponding to the cylinder number. If it does not, it'll output a code 9.

5)If you want, you can press the gas pedal again, and it'll re-run the test with looser specifications..so you can see how bad the cylinder really is. If it doesn't detect that cylinder again, you know that the cylinder isn't so bad. If it does, you know it's pretty bad. You can go for a third round of testing (with even looser specifications) by pressing the gas pedal again and if it detects that cylinder on the 3rd test, it's really bad.

My manual says that the cylinder balance test "won't always identify a bad injector"....
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Old 12-27-2004, 01:14 PM   #21
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Yeah, we did the cylinder balance test, no weak cylinder found. Tried it 2 or 3 times. Did your car smooth out with the new injectors? I am still wondering if replacing O2 sensors will fix my problem as the car does it in closed or open loop. I thought the O2 sensors were not used for input during open loop or warm up. Still the only codes I get are thermactor failure and disconnecting the air pump hose does smooth it out a little bit but not entirely.

Only sensors I didn't sub were: Air charge temp, coolant temp, TPS(car has a new one and it didn't change anyway) and O2 sensors.

I have not checked fuel pressure, the fuel filter has never been changed as far as I know either. Car never cuts out at high rpm or load though.

Engine has a rough chop to it, even noticeable at highway speeds in overdrive.
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Old 12-27-2004, 03:22 PM   #22
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The new injectors made the idle smoother. They also made it start faster. I haven't replaced the faulty thermactor solenoids yet, that should make the idle even smoother.

I believe the computer applies the fuel trim correction learned through the oxygen sensors to all operating modes (including cold startup and WOT) so the only way to eliminate the oxygen sensors as the source of the problem is to disconnect them and then disconnect the battery for several minutes to ease the EEC's learned fuel trim data. Then see how it behaves with them disconnected and the default fuel trim data.

You could also try disconnecting the MAF and see if that helps. It will run with the MAF disconnected, if the problem goes away you might suspect the MAF.

The air charge and engine coolant temp sensors have the same temperature/resistance curve so they should read close to the same resistance on a cold engine.
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Old 12-27-2004, 03:42 PM   #23
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Ok so even if the o2's aren't correcting the fuel/timing in open loop the computer is probably using the stored data that the o2's supply during closed loop and then somehow applies them during the next cold start up? Sounds plausible as the engine's fuel/timing requirments are gonna change with age and this is suppossed to be an adaptive set up.

Will try the O2/disconnect and clear the computer's memory.
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Old 12-27-2004, 03:57 PM   #24
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That's correct.

Also, because of the adaptive system, sometimes clearing the computer's memory will fix strange problems. It's like it either adapts wrong or the memory got corrupted somehow.
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Old 12-27-2004, 04:07 PM   #25
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do you still have the stock h-pipe on the car?
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Old 12-27-2004, 04:55 PM   #26
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Quote:
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do you still have the stock h-pipe on the car?
Yeah, everything is stock and in place. Still has air pump too. Stock air box, pretty much the way Henry built it.
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Old 12-27-2004, 06:43 PM   #27
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I have a thought here, I have changed a butt load of stock heads. When I take off the heads, the exhaust holes at the back of the heads are almost always clogged. If you are cruzing and this thing starts messing up, my guess is that the EGR is opening, (advancing timing and cutting fuel). When this happens, the EEC see's the valve opening and makes the timing fuel changes. If the holes are pluged, the eec might be leaning the car out too much ??? Just an idea here. What I do sometimes to fix this is plug the vac line to the EGR. This is the EGR positioner sensor. If it can't see it moving , it won't change anything. Again, Just a thought here, I am more of a flat out performance guy compaired to drivability. Drivability is much harder.

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Old 12-27-2004, 09:13 PM   #28
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To test the EGR to see if plugging is a problem, apply vacuum to the EGR valve with the engine running. It should stumble--you probably won't be able to make it stall. At least I couldn't make mine stall when I tested it. But it passes the NOx part of the emissions dyno test so I know the EGR valve is working...
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Old 12-27-2004, 09:22 PM   #29
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By the way, I got the new TAB / TAD solenoids and there is definitely supposed to be NO vacuum when these solenoids are not getting power.

Which means that my old TAB / TAD solenoids are definitely shot.
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Old 12-27-2004, 10:48 PM   #30
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The EGR operation as stated above; I have been through this already is a different way.
If you have an adjustable fuel regulator, put a gage on and set the pressure up about 4 psi.
If the EGR is plugged causing leanness, the increae in fuel pressure should cover it or at least reduce the problem a noticable amount.
The Ox sensors won't re-adjust injection for this an most believe.
I run a K.B. blower and ran into this with the extra air the blower pushes at low load and cruise. I blocked the EGR with a metal gasket to prevent the gas from flowing into the intake making it worse. Raised the fuel pressure to cover, and hesitation has never been back. I now run about 44 psi without any problem for the last year and a half and no computer codes
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Old 12-27-2004, 11:07 PM   #31
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The air pump system works as follows:
Air from the pump goes to the TAB. This valve either passes the air to the TAD or vents it to the outside depending on what the EEC directs for the running engine condition.
The TAD either directs the air to the heads or to the cats not both at the same time.
The EEC can't read where the air goes but only looks at the 'electrical presence' of the solenoids.
There is no vacuum involved in this operation. It's purely air direction control from the EEC operating the TAB and TAD solenoid.
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Old 12-27-2004, 11:47 PM   #32
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Quote:
Originally Posted by Bluegrass
The EEC can't read where the air goes but only looks at the 'electrical presence' of the solenoids.
There is no vacuum involved in this operation. It's purely air direction control from the EEC operating the TAB and TAD solenoid.
Yes, it can read where the air goes. Otherwise, how would it give code 45 (thermactor air always upstream during KOER test) and codes 94/44 (AIR system inoperative)? I can MAKE code 94/44 happen just by plugging the vacuum line to the diverter valve and running a KOER test.

I would also guess that I could MAKE code 45 happen by applying vacuum to the diverter valve and running a KOER test...

..which leads me to...there is vacuum involved in this operation. The solenoids control whether there is a vacuum applied to the valves. They are known for sticking and applying vacuum to the valves when they're not supposed to be.

In fact, the EEC-IV handbook (available for purchase from http://www.dalidesign.com ) states:

"If you are getting lean fuel codes along with thermactor codes then suspect the O2S. The PCM cannot tell if the thermactor is switching if the oxygen sensor is not reading correctly."
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Old 12-28-2004, 12:11 AM   #33
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Well I don't know what book your looking at. My book by Probst page 299 on the TAB/TAD valves are solely electrical in operation.
There is no vacuum involved in there operation like the EGR has. Each valve has only two ports to pass the air from the pump in and out.
The EEC signal to these valves are all that is needed to make the system work for the car in question.
Look at page 328 to see the EFI drawing that shows the TAB and TAD being directly operated from pins 32 and 38 off the EEC.
The EEC can only tell the operation of the primary system by these valves.
It may be possible that by secondary "result" that the EEC may report an excessive or insuficient air condition under some conditions but only indirectly.
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Old 12-28-2004, 10:38 AM   #34
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Quote:
Originally Posted by Bluegrass
Well I don't know what book your looking at. My book by Probst page 299 on the TAB/TAD valves are solely electrical in operation.
There is no vacuum involved in there operation like the EGR has. Each valve has only two ports to pass the air from the pump in and out.
The Probst book is a good book, but there are a few things in it which are just plain wrong. That is one of them.

There is vacuum involved in the operation, just like the EGR valve. In fact the vacuum solenoids are mounted right under the EGR vacuum regulator solenoid.

As far as what books I looked at (I also looked at my 1988 Mustang 5.0 and it's exactly as I have described. The vacuum hose routing diagram on the plastic ignition coil cover also shows the TAB/TAD solenoids with vacuum hooked up...):

Ford 1992 Powertrain Control/Emissions Diagnosis manual (the same one the dealer has)

An EEC-IV diagnostic/training manual that my mechanic has (don't remember the title, but it's from 1992 and probably out of print by now). This is the ONLY book I've found that describes WHEN the thermactor air is supposed to go into bypass and when it's supposed to divert upstream and when it's supposed to divert downstream.

The EEC-IV handbook I mentioned earlier

As far as tests go, during a KOER test, the EEC-IV does use the oxygen sensors to partly test the operation of the thermactor air solenoids and the diverter/bypass valve. The air diverting upstream should make the oxygen sensors read lean, BUT it cannot tell if the air is diverting downstream or if it's just not there.

It'll give a code 44/94 when the computer diverts the air upstream and sees no lean response from the oxygen sensor. The air could be missing, could be stuck downstream, could be stuck bypassing, it doesn't know.

It'll give a code 45 when the computer diverts the air downstream and the oxygen sensor continues to read lean. The air is there, but won't go downstream when it's supposed to. (EDIT: sometimes it will give a code 41/91 instead, indicating that the oxygen sensors are reading lean. I stated above that it was giving code 41/91 until I replaced the fuel injectors and the fuel pressure regulator, and now it is giving a code 45 instead.)
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Old 12-28-2004, 10:55 AM   #35
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just curious,
have you tried checking your harmonic balancer? ive seen many start to spin internally thus giving unfavorable harmonics. to check. mark the inside and outside of the balancer. give it a whirl a few times. make sure the lines are marked the same as you just marked. if its off. theres your problem
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