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Discussion Starter #1
Put my car on the dyno yesterday. Car runs fine at idle and light throttle but as soon as boost comes on it cuts out and bucks.

Combo:

.040 stock short block, f303 cam, edelbrock performer heads with 5845 roller springs. Explorer upper/lower, 65mm throttle body. 42lb injectors, 255lph pump. Msd 6al ignition, blaster coil. Stock distributor w/ msd cap/rotor. Auto lite 3923's gapped to .028. Ford racing plug wires.



So far I have tried swapping plugs, wires, coil. Disconnected 6al and ran off the factory computer. Still cuts out.
 

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How much boost does it start at? I for one would also change out the wires from ford racing to a good quality wire such as MSD or Taylor and switch to an NGK plug. I always ran Autolite but when I went turbo I started having issues with them and have heard many others having recent problems with them. The FR wires have a tendency to have ohm resistance problems. May not be your problem but I would start there. You may have a wiring issue also. Might be something not showing it's there until the demand and resistance levels spike.
 

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How does the air/fuel ratio look when this happens? My car was going lean and would fall on its face when it went lean.
 
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How does the air/fuel ratio look when this happens? My car was going lean and would fall on its face when it went lean.
+1

Could be fuel, since you have swapped ignitions and wires with no change.

Do you have any way to monitor air-fuel ratio or fuel pressure when doing a pull?? Be real careful, if it is running out of fuel you can damage the engine.
 

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the gap is too big... you are likely blowing out the spark

try a gap at around .020 for boost

you are also likely going to be pushing the limits of the 255 pump and those 43 lb injectors...
so just be careful and pay attention to the fuel pressure and to the Air fuel ratio


after you gap the plugs tighter...if fuel pressure stays stable, and Injector duty cycle is still below 90%, and you have to throw a bunch of fuel at it to get the Air fuel in line, that shows you are blowing out spark still, and may need to address the plug wires, distributor/coil
 

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Discussion Starter #6
How much boost does it start at? I for one would also change out the wires from ford racing to a good quality wire such as MSD or Taylor and switch to an NGK plug. I always ran Autolite but when I went turbo I started having issues with them and have heard many others having recent problems with them. The FR wires have a tendency to have ohm resistance problems. May not be your problem but I would start there. You may have a wiring issue also. Might be something not showing it's there until the demand and resistance levels spike.

1-2lbs. As soon as boost comes on it cuts out.
I've ran the ford wires for years with never an issue. Same thing goes for the auto lites
This is a whole new motor. Old motor was just a stock '86 long block that took 16psi on a regular basis. Never had an issue like this.
 

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Discussion Starter #7
How does the air/fuel ratio look when this happens? My car was going lean and would fall on its face when it went lean.

Fuel pressure comes right up, tough to read air/fuel since it happens so quick with such little throttle.
 

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Discussion Starter #8
the gap is too big... you are likely blowing out the spark



try a gap at around .020 for boost



you are also likely going to be pushing the limits of the 255 pump and those 43 lb injectors...

so just be careful and pay attention to the fuel pressure and to the Air fuel ratio





after you gap the plugs tighter...if fuel pressure stays stable, and Injector duty cycle is still below 90%, and you have to throw a bunch of fuel at it to get the Air fuel in line, that shows you are blowing out spark still, and may need to address the plug wires, distributor/coil

Don't want to question your knowledge because I originally thought spark blow out, however it happens real low in the rpm's with not a lot of throttle so not a ton of air getting in. Also I know with my old engine, I ran the plugs at .030 and pushed it to 16+psi and never had spark blow out. Also know that engine had very restrictive heads and a baby cam but still 16psi is a lot of air being forced in.
 

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Discussion Starter #9
Swapped out distributor today with a band new one. Still acted up. Watched fuel pressure gauge and that climbed nicely to 50psi before I got out of it.
Tough to read wide band cause once it cuts out the reading is all over the place.
Going to try closing the gap some tomorrow and see
 

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I know you said you've never had an issue with AL plugs and neither did I until I threw the turbo on. I was eating 3923's like tic tac's. Switched to the NGK and no more issues. Same set in there since last summer, bunch of track runs, lots of street miles and 93 and 110 gas. .028 gap and 14 psi and a very safe tune.
 

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Discussion Starter #11
I know you said you've never had an issue with AL plugs and neither did I until I threw the turbo on. I was eating 3923's like tic tac's. Switched to the NGK and no more issues. Same set in there since last summer, bunch of track runs, lots of street miles and 93 and 110 gas. .028 gap and 14 psi and a very safe tune.

Tr5's?
 

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No R5671A-8, stock number 4554
 

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Could still be spark blow out. On my 94, when I swapped the engine and went turbo, I did not hook the Mallory 685 back up. My stock ignition would run fine at light and part throttle but give it any more and it would fall on its face. I would think if your MSD was working correctly, it would easily handle .028 of plug gap with that little of boost. Something to think about if switching plugs doesn't help.
 

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On the other hand, I ran 24 psi with the stock Ford TFI ignition and Motorsport wires with .032 gap, and never had an issue. Only change was a MSD TFI coil.

With a CD ignition box I can run any gap I want (within reason, I have not tried .045 or more LOL) and not have "blow out".

Since you have issues at part throttle and have swapped dizzy's (which I assume means TFI and PIP), I would look at things like the grounding.

I've been doing this off and on for 48 years, and have yet to have an engine critical for plug gap. :) That aside, since to have a light throttle low speed issue, you are wasting time with gap and plugs (unless they are broken).

You may have to put a scope on it.
 

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Discussion Starter #15
Today I did close them up to .020. That didn't help any. I was able to get a better look at my wide band and was seeing 13's! I turned up my fuel pressure and that seemed to help but still has a stutter.
Going to put the plugs back to .028 and see how that works

Also called edelbrock and asked about my combo. They said those springs should have no problem with my cam/combo.
 

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Discussion Starter #16
Well today regapped my plugs back up and kept the fuel pressure up. Still no change.
Starting to question my old performer heads. Wondering if the valves are worn enough to creat a leak.
Noticed today some intake backfire
 

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Intake popping sounds like a lean issue, but I still think you have another electrical issue going on. Just touching the throttle lightly and it causes a cut out seems like there's another issue and I don't think it's your heads. Have you checked your tps voltage, maf sensor voltage? Gone over the grounds and making sure the contact is tight and clean.
 

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Discussion Starter #18
Intake popping sounds like a lean issue, but I still think you have another electrical issue going on. Just touching the throttle lightly and it causes a cut out seems like there's another issue and I don't think it's your heads. Have you checked your tps voltage, maf sensor voltage? Gone over the grounds and making sure the contact is tight and clean.

Haven't checked any voltage. I've checked the grounds but I'll check them again.
As for voltage, what should I look for on the tps and maf? Also, how do I check the maf voltage?
 

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Possible

wrong firing order

lack of fuel

A big pump and big fuel lines, and big injectors really mean nothing, if the ECM commands little pulses.

Do you have access to the stock 02 sensor voltages? they are far better to use for diagnosis.
 

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Discussion Starter #20
Possible



wrong firing order



lack of fuel



A big pump and big fuel lines, and big injectors really mean nothing, if the ECM commands little pulses.



Do you have access to the stock 02 sensor voltages? they are far better to use for diagnosis.

If it was wrong firing order wouldn't it run like crap all the time? I only have a problem under load.

Have fuel pressure turned way up and have air fuel of 11.7 at wot.

O2's are turned off
 
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