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Discussion Starter #1
I’m going nuts here with this thing. I think I’m overlooking something stupid but hopefully someone might remind me what I’m missing here. Long story short, I blew headgaskets last fall, ( engine is basically a stock shortblock, ported GT40 heads/ intake, acufab 70mm throttle body, 3” Pro M blow through tube, and On3 turbo kit and tuning with PMS series 4). I pulled the engine to fix head gaskets and replace an oil pan gasket. When i put the vehicle back together it runs but sort of rough. It will basicallly fall flat on its face when I try to accelerate under a load. I can watch the wide band go from super lean to pig rich, and that’s when it will run and cut out. With the spout out it will not idle when it’s warm.
I have so far:
- verified fuel pressure ( 40psi with vacuum line disconnected, 35 at idle, connected)
- smoke tested for vacuum leaks
- verified O2 sensors are plugged in lol
-maf is plugged in and reading
-Cleaned salt and pepper connectors
-Replaced cap and rotor
-I put new plugs in with the engine ( Autolite Iridium)
-set tps voltage to .97
-Set base timing at 10 degrees
- removed and cleaned Maf
- verify engine grounds

I do not have any codes because my check engine light bulb doesn’t work and I don’t have a obd1 scan tool. I am going to probably clean the maf again and triple double check. What else am I missing here? Thanks in advance


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How was driveability before you blew the head gasket? Has it ever ran good? What is new since the head gasket repair?

If this was just put together I would lean towards the mass air meter.

If it ran like craps before blowing the hg I would remove the pms and run it and see how well it runs with your current meter and go from there.
 

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Discussion Starter #3
It ran real good before the head gaskets, ( too good lol). I swapped:
-camshaft, went from an E cam to stocker with 1.7. Rockers
-Throttle body ,75mm acufab to 70mm
- upper intake, cobra to tubular gt40

Pretty sure that’s it. I’m just wondering if there is some trash blowing around and contaminating my Maf? I don’t know. I’m running out of ideas.


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Discussion Starter #5
check the tune

log 02 and fuel trims


I don’t have a way to datalog but I can check what the O2s are reading and let you know. Cold/ warm, left/ right if that helps.


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Since it ran well prior to hg, I would think your meter is close enough to be fine tuned by the pms.

Why did the hg blow? Too much timing, lean, etc?

I know you checked, but I would look extra hard for a vacuum leak.

Also, I like to check each header an inch to from the head for consistent temps with an infrared thermometer.
 

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Discussion Starter #7
Since it ran well prior to hg, I would think your meter is close enough to be fine tuned by the pms.



Why did the hg blow? Too much timing, lean, etc?



I know you checked, but I would look extra hard for a vacuum leak.



Also, I like to check each header an inch to from the head for consistent temps with an infrared thermometer.


That’s a great idea about checking temps on the headers. I will do that tomorrow. I will check again for a vacuum leak. I might pull the plugs also. This thing is weird. Almost like it’s low on fuel, then almost clears up but the data it’s showing me on the PMS screen all looks good. Either way it’s running. That’s when I figured it had to be fuel related. Put the gauge on and that looks good also. I could have sworn it was a low fuel pressure issue but the gauge proved me wrong I guess.


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Ist ideas...
Long time ago I had an issue where the fitting on the tubular bottom was hitting the drivers valve cover and I had to grind the vacuum fitting down to clear. That is without a spacer. Tubular can also be tight on the injectors without a spacer.

I have found so many issues with my infrared thermometer. Much more accurate than my fingers.
 

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Discussion Starter #9
I’m running an intake spacer just for that reason with that same fitting your talking about. Haha


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If you've still got the oem wiring harness & obd1 port in place,you don't need a scanner or the cel to run the code tests.Just use a jumper wire & 12v test light.
1) Connect one end of the jumper wire to the STI terminal and connect the other end of the jumper wire to the SIGNAL RETURN terminal (@ the diagnostic port)
2) Now connect the test light clip to the (+) battery post/terminal and insert the test light probe into the STO terminal (@ the diagnostic port)
3) Turn the koeo & the code test will begin.
 

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Discussion Starter #12
If you've still got the oem wiring harness & obd1 port in place,you don't need a scanner or the cel to run the code tests.Just use a jumper wire & 12v test light.

1) Connect one end of the jumper wire to the STI terminal and connect the other end of the jumper wire to the SIGNAL RETURN terminal (@ the diagnostic port)

2) Now connect the test light clip to the (+) battery post/terminal and insert the test light probe into the STO terminal (@ the diagnostic port)

3) Turn the koeo & the code test will begin.


I’ll try that tonight, thanks


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Make sure youve got the hego ground wire attached to a rear intake bolt,rear cylinder head
bolt (i.e. - crossover pipe bolt) etc.It'll trigger the o2 sensors to read lean if its not connected.Its the orange wire with a ring terminal on the injector harness.Im not familiar with how the pms works compared to the factory ecu,but if it doesn't have a screen you can look at to view live data,I would ohm out the ect sensor,with the engine cold & hot.If the ect is bad,it will tell the ecu that coolant temp is much warmer than what it truly is and that will trigger the ecu to lean the fuel mixture.Were you ever able to pinpoint the true cause of the blown gaskets?? Could it have been caused by a bad adjustment in the tuning?? I always thought it was usually just one gasket that would bite the dust when an engine suffered from a detonation episode,but you got had a double whammy.I would definitely check the old plugs for lean signs.Make sure youve got your pcv system set up correctly too,so that it wont pressurize the crankcase.If there is enough unmetered air allowed into the engine,it will also trigger a lean condition.Just like a breathered oil filler cap does if the pcv system is setup in stock form.
 

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I gapped then at .030”


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When I got my motor running, I went .030 as well. After awhile, it started to break up in boost just like you described. I pulled them and a few of them opened up as much a .004 at only like 3k miles. That seems to be the limit for my setup.

I'll just go .020 with this next set.
 

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Discussion Starter #16
Make sure youve got the hego ground wire attached to a rear intake bolt,rear cylinder head

bolt (i.e. - crossover pipe bolt) etc.It'll trigger the o2 sensors to read lean if its not connected.Its the orange wire with a ring terminal on the injector harness.Im not familiar with how the pms works compared to the factory ecu,but if it doesn't have a screen you can look at to view live data,I would ohm out the ect sensor,with the engine cold & hot.If the ect is bad,it will tell the ecu that coolant temp is much warmer than what it truly is and that will trigger the ecu to lean the fuel mixture.Were you ever able to pinpoint the true cause of the blown gaskets?? Could it have been caused by a bad adjustment in the tuning?? I always thought it was usually just one gasket that would bite the dust when an engine suffered from a detonation episode,but you got had a double whammy.I would definitely check the old plugs for lean signs.Make sure youve got your pcv system set up correctly too,so that it wont pressurize the crankcase.If there is enough unmetered air allowed into the engine,it will also trigger a lean condition.Just like a breathered oil filler cap does if the pcv system is setup in stock form.


Yea I did actually only have one side leak, cylinders 3,4. I can monitor the O2s live on the PMS. I took a couple of snap shots with my phone of it today. I had a small window of time between work and work lol. I removed he Maf again and cleaned it again just to be 100% sure that wasn’t it. Car ran a little bit better then it started to act up again once I tried to give it throttle. I checked header temps when it was warm and all were within 30 degrees of each other. Around 380-400 degrees right after the header flange. I really didn’t find anything else new today. More dead ends with the small amount of time I had.


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Discussion Starter #17
I still want to check codes, and I want to pull the plugs and see what they look like. It acts like it a fuel delivery problem.... I might check the fuel lines and rails to make sure there isn’t a restriction. I would figure I’d have fluctuated fuel pressures but who knows at this point.

This picture is of when this thing was running rough. I was tipping the throttle in at 5% and it wouldn’t rev up. Maybe this would help someone? I do t know


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Discussion Starter #18

Incase someone doesn’t know what these are


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The 02s show .00v. It should be around .5v

Why is your timing 35 degrees at 900rpm?

Try to disconnect the 02s and see if it runs any richer.

Vacuum seems low?

Is tps adjusted properly in the pms?

It has been 11-12 years since I ran a PMS, it's coming back slowly lol
 

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Discussion Starter #20

This is how it looked when it cleared up. Idle is normally around 800


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