Engine Dies And Backfires At Wot

Feb 8, 2018
1993 Mustang LX 5.0 manual. This is my son’s first car. It is a father/son project. It was wrecked in the front pretty bad when he bought it. We restored it ourselves and it is his daily driver. It was said to been bored .40 over. No records provided of build. It runs and idles well. The problem is when we floor it, it is fine through first gear into second. At the end of second, it will instantly kill. Then usually a brief check engine light followed by a backfire. Then it resumes as normal. We were thinking it was a fuel problem and replaced the fuel pump with 225lph. Replaced distributor because it died out of the blue on the road and left him stranded. Replacing that fixed the WOT problem. It ran very well. Now 4 months later it is dying at WOT again after 2nd gear. We are thinking it could be the distributor bottoming out onto the oil pump and may need to be shimmed? The timing is correct. There’s no break up before it dies. We just can’t find any info of anyone having this problem. We can’t understand what would cause it to need a new distributor so soon and why it doesn’t cut off in 1st gear at WOT. Only at the end of second. If we baby it through second, the hit it again, it will die at the end of 3rd with same brief check engine and backfire.
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Sorry to hear your having this problem, first thing to do is check for codes, you can have stored codes without the check engine light being on, on the main page of the 5.0 tech page just below the header are sticky threads for tech stuff, you will find jrichker's how to check for codes, it's step by step and you don't need a reader but the code reader in the thread is very inexpensive, list the codes and we can help from there.
Post some pics of your stang too, father/son projects get special treatment.
Not really.
Well, maybe sometimes.
Ok almost never, but I'll but in a good word for ya. :jester:
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Kartheif, I will check for codes tomorrow when he gets home. Last time, before the new distributor, we did a code check and there were none. (Can you believe that?)
Seems if the light comes on even for a half second, there should be a code. But that was then...
Thanks for your interest!
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You should get a 11 if nothing is stored, something is up if you get a cel and no code I would suspect a computer problem.
In the tech/how to section there is a surging idle checklist and a no start checklist that will help diagnose problems, one thing I always suggest to check are grounds, there are 4 that are very important on these computer controlled cars, specifically frontend damage, one ground runs from the battery negative to the fender apron between the battery and the starter solenoid with another wire from there to a cylindrical connector then into the wire harness by the framrail. All this is covered in the checklists, remember that grounds need clean attaching points, they should be attached to the block/heads for best results,
If the light is coming on you should get a code stored in continuous memory.

Remember it's not like obd2. You should get two pass codes with engine off and then start the engine and get an additional code 11

When you changed the fuel pump, was the baffle intact and secured to the tank?
To clarify I did get end of test code 11. However, I didn’t get a stored trouble code. The baffle was intact when we changed the fuel pump.
The car just choked down on me today and would not run. It would turn over but it would not hit. I smelled raw fuel and suspected no spark situation. We checked the distributor for spark and there was none. We pulled the distributor to inspect and found the distributor shaft was very hard to turn. With it being only 10 months old, we returned it and got a replacement. We put it in and it fired right up without hesitation. Just curious if there is something else that would cause distributors to fail on this vehicle? The distributor gear looked very good and the wear pattern was centered. We are thinking of chalking it up to a defective distributor. The first distributor was OEM and was probably the original. The one that just failed was Spectra premium. And of course this one just installed was the Spectra premium replacement.
After replacing the distributor our car stopped shutting down at high rpm with WOT for a couple weeks. It has come back as expected just like before. When it gets into higher rpms with WOT, it kills gives brief check engine light and restarts when clutch is let out. We checked codes. There were a rash of codes. Most were coolant temp from doing work on fans months ago and MAF from forgetting to plug in the sensor after cleaning the filter...We decided since it had been a long time since codes were checked to just undo the negative battery cable for 30 minutes to clear codes. After clearing, we took it up the road and let it do it’s shut down at WOT. We checked for codes when we came back. We only got “11”. We checked the TPS next. It showed .94 sitting and 4.93 at WOT. SOMETHING is triggering it to kill but nothing is pointing us in the direction of a cause, with the exception of a couple weeks of a fresh distributor install. We are simply stumped!
It starts fine. After it dies and the clutch is pressed in and let out, it gives a backfire most times and resumes as normal. After time it’s like the distributor degrades and eventually fails. The car runs great otherwise. Only other complaint with it would be at idle you can feel a very slight misfire from time to time.
After resetting the codes by disconnecting the battery and taking it up the road to let it give it’s fault, we only got the 11 codes. We did the run code test. It gave the 4 pulses idled high then gave the 1 and 1 pulses. Thanks for your support guys. If we can get this figured out, we will feel better about this being his daily driver to school.
I think you need to go over the wiring, including the fusable links. It was wrecked right?
It’s worth revisiting. We went through it checking grounds and fusable links when we first discovered it would do this. The only wiring that was messed up was the airbag sensors on the front. The wiring that led to them on the passenger side at the shock tower was busted. The other relays mounted there ( I think there’s 2 others) are untouched. The wiring that was busted had a cylinder type connector with 2 or 3 prongs inside. I can post a pic if this sounds significant.
Please post ALL of the numerical code values so that we can have a detailed view of what is going on.
Are you referring to trouble codes that show up? We plan to try it again tomorrow and see if when it shuts down it will save a code. Right now, the CEL comes on just before it dies but nothing is stored when we read the codes. Only the “11”. I know it is storing codes from the initial codes we got from accidentally forgetting to plug the MAF sensor a few months ago before we reset it.
Let me know if you are referring to something else. I will post again tomorrow after we try it.
Post it up. I think there is a significant relay in that area but can't remember what it's for. If you need help with wiring identification go to veryuseful.com
I will get a pic up tomorrow after we work with it. Seems like there’s a WOT cut out for the A/C relay there if I can remember right.
Another point that lingers is the fact that the PO said it was bored .40 over. (No proof of build or receipts). My son and I have talked through possibilities of the cam not being installed at correct degree or old weak springs reinstalled or who knows right? One thing that didn’t add up when we started on this project was the fact it had 17lb injectors in it. We thought Ahaa! That’s the problem, pushing injectors past 100% cycle duty. Nope! We put in correct injectors and no change. The only thing to have affected the WOT cut out at high rpm is a fresh distributor for a couple weeks. Lol
Sorry it’s just becoming comical to us. We have had a lot of fun rebuilding this car and have learned a lot about it and each other. We look for the day when it is figured out.

This is a pic of the busted wiring at the passenger shock tower under the intake tube. I’m pretty sure it went to the airbag sensors.
We had a discovery of what conditions would cause it to die. We thought at WOT and high rpm. My son discovered that if he floored it without upshifting, it would give a CEL earlier and stay on longer. It would also die at a lower rpm and backfire. So it seems to be the “strain” of accelerating that’s causing the issue. It will redline through 1st with no problems. 2nd gear through will die or cutback. We have video of this and will get it posted soon. We were also successful in pulling codes 18 & 53. TPS sensor and SPOUT open circuit. The TPS makes sense to our situation. The SPOUT has the dongle inserted so that’s confusing.
We plan to check out from the SPOUT connector to pin 38 (if I recall correctly from another jrichker post) at the computer. That’s our starting point because we have checked the TPS. If the Spout is not right we believe the timing can’t adjust when heavy accelerating is called for. It that makes sense.