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Discussion Starter · #1 · (Edited)
OK, the car is a 87 lx but has a complete 89 mass air engine/computer harness,computer is an 89 A9L. mods are longtubes, b cam, 1.7rr, all smog equipment removed, adj fuel pressure reg. set at 40psi, C&L 76mm maf, k&n conical. the other mods would not effect it. Well when i first start the car it idles and revs fine, as soon as i get out of the driveway and about an 1/8 mi down the road the car starts to run rough, pops back throught the intake and will carry on like this for about 1-2 min. or about another 1/2 mi. then will run like a charm again with no sign of any problem. It will do this at 1/4 throttle to wide open with no difference, still pops back. The fuel pressure stays consistant at 38-40 psi the whole time. Engine temp is 160-180 at the time it is doing it if that matters. Timing was set at 12 degrees and does not flutter so i know its not timing chain related. Also changed the ECT sensor, New plugs, new motorsport wires, new msd cap and rotor,new fuel filter, changed all Vac. lines to assure no leaks and checked all grounds. Also does this with the stock maf meter in place. Any help will be greatly appreciated. Thanks....
 

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I know what you mean...

I have the exact same problems and have searched high and low to remedy the situation. This is what I tried:

1) I ended up re-adjusting my roller rockers. I was told they may be a little tight, leaving the intake valve slightly open during firing. This so far has seem to clear the problem. I was using the Crane method which seemed to be fine and has worked well in the past, but I found a more accurate method on this website(Search for "Valve adjustment for dummies"). A guy named Nick has a method which Ed Curtis agrees with. It is supposively a more accurate method of adjusting and has worked for me.

2) I did find a vacuum leak under one of my valve covers. It was slightly warped and not sealing correctly. That is corrected.

3) My timing is set at 14BTDC. My car runs fine there. I had dropped down to 12BTDC and the the car ran fine but had less power. I returned it to 14. I have not checked my total advance.

4) My FP is at 40psi. I have tried 38-42psi as well.

As of yesterday, it seemed to be running fine. I got on it hard as it was cold right out of the driveway and to my surprise it didn't backfire or sputter at all. Boy was I thrilled. I think item No. 1 was the cure. I didn't start it today. I will test it again tomorrow. I'll post the results for ya!

Hope this helps!

If it fails tomorrow, I will be replacing the ECT and Air temp unit(on intake).

Later.
 

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Discussion Starter · #5 ·
I think I found my problem but dont want to spend the money first without opinions, I noticed that the o2 sensors I put on when i dropped the motor in are 2 wire but if i can remember correctly aren't they supposed to be 3 wire? Could that be causing my problem? If so what does the 3rd wire do? the only wires coming out of the sensor are1 black and 1 white, they are bosh(sp?) sensors. Thanks
 

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I had the same problem and it turned out to be a bad gasket between the upper and lower intake. Either way if its backfiring through the intake then thats a lean condition. Check for leaks.
 

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Discussion Starter · #9 ·
I know the ones that Autozone gave me are two wire but If I noticed that on my freinds they are 3 wire? is the 3rd wire for the heat element? Just wondering if the two wire o2 sensors could be causing the lean mixture if they are not heated and the computer is looking for a signal from a heated one? Just dont want to waste the $95 for two more since i just put these in about 500 miles ago. Which is when i put the engine/computer/harness in and the problem started, The drivetrain ran great with no problems in the car I pulled it from. I didnt change anything else in the swap except for Longtubes, the o2 sensors new wires, cap, rotor and plugs. engine and trans were pulled and installed complete and engine harness was on the motor the whole time during the swap which is leading me to believe it may be the 02 sensors. I changed the plugs again incase i had a faulty plug( has happened before) and still the same problem. I also noticed that when i pulled the plugs that the plugs on the right side of the motor were cleaner , than those on the drives side. none were fouled just tan-brown colored, while the ones on the right side still had a shine to the top of the plug electrode. Any clues?
 
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