breaking up under boost

[williamb82]

due to some issues we are having with a friends car. can you use a 89 ecu on say a 90, or 91, 92 etc.. engine harness? the harness he bought is supposed to be an 89 harness. but idk. we have tried 3 diff ecu's that are all supposed to be 89 ecu's,. and same problem. it breaks up really bad under boost.

it is a stock rebuilt 7mgte with mhg and arp's, stock ct26. fmic with 2.5in piping. no vac leaks at all. this is in a toyota pickup. we have tried known good parts from my 7mgte when it was on stock electronics. have tried cps, coils, ignitor, tps, coolant sensor, cold start switch, 3 diff ecu's as mentioned before. another afm, etc... it seems to be running pig rich. smells like it anyway. im lost at this point as the ecu is throwing no codes at all. we even used a voltage tester on the engine harness plug itself thinking somehow the enging light wiring was wrong. no codes. runs and idles smooth. just when driving it breaks up bad. timing is at 10deg. cam timing is perfect. had him regap the plugs from stock gap of 32 thousandths to 28. same, no change. its all stock except the i/c, pipes, and 3in downpipe.

anyone got any ideas/ all i can think of is its an issue with the harness not being an 89 like it was supposed to be or something.

 

[jdub]

What is the fuel pressure?

Condition of the plug wires? Tested/inspected the coils for cracks?

 

[williamb82]

coils are fine. no cracks. plug wires are new msd wires. idk the fuel pressure. but you think it might be dropping under boost? that was one of my thoughts and was thinking of replacing the fuel line with a 3/8ths line from pump to rail. we are using a walbro 255lph pump and the j tube is bypassed.

 

[jdub]

Actually, I'm thinking the FPR is supplying too much fuel under boost...with a Walbro pump on a stock FPR (even with the J tube bypassed) and it running pig rich, it's worth looking at.

What size injectors? Were they flow tested?

 

[williamb82]

stock 440cc/min injectors. i never had that issue on mine when i put the walbro in with stock injectors. but pig rich shouldnt make it breakup and pop like that. sounds like spark blowout almost. its wierd.

 

[jdub]

By "pop" you mean a misfire...as in the exhaust/CAT?

Are all the ECU sensors hooked up or adapted to the truck? Including the ones outside the engine bay (i.e. the speed sensor, etc)

 

[williamb82]

speed sensor isnt hooked up. i never had it hooked up on mine either. and its not a misfire persay. its very light popping. its open dp. no cat. almost like a ping but not quite.

 

[jdub]

"Very light popping" = "when driving it breaks up bad"

I still think it's fuel related...but, I'm getting a mixed description from you. Your saying it's rich, but you describe lean. BTW - it is very possible to have a rich misfire.

I realize your motor is using 440 injectors on a Walbro with no problem...that didn't answer the question. I asked if the ones on this motor were flow tested...if they are leaking or not sealed to the rail properly, you will smell gas. If they are not putting out the rated output, you will run lean.

It helps if you answer the question vs assuming I am talking about something else. Just because your injectors are fine doesn't mean these are. Same goes for the FPR...it needs to be tested.

Are you using AutoLite 3923 plugs?

 

[williamb82]

idk what plugs he is using. and no his injectors werent tested. i guess ill try to find one of my fpr's to test on it after we replace the fuel line. we wanted to redo the stock truck line to make it cleaner anyway. we will have to check it out. ill have him drive it today and shut it off while its popping so we can check one of the plugs for a lean condition.

 

[oldsking]

Yeah sounds like a problem with fuel to me, plugs can tell you wonders of a story. I recommend placing a picture of them after you pull

 

[williamb82]

ill try to get some. idk if ill be able to though. going after work. im running 780's now so if his injectors are bad ill just try to find my old ones for him.

 

[paradox616]

Did you check the grounding strap for the coils? it will "break up" under load and you wont ignite all your fuel... id inspect the resistance between the base of the coil packs and the chassis,

has it still got the stock J pipe restriction? (this limits fuel flow to maintain a basic fuel pressure on the return hose incase the reg fails)

not discounting from what jdub said but there is 3 things it could be

electrical related = follow the TSRM and measure resistance of electronic components as specified
fuel related = get a fuel pressure gauge on there, maybe try a different reg
compression related = do a comp test to rule out mechanical failure, also its very likely it could be a boost leak, i know you tested it for leaks but you may have a blow inlet manifold gasket you cant spot.. i had perfect vacume as well,

 

[jdub]

Did you check the grounding strap for the coils? it will "break up" under load and you wont ignite all your fuel... id inspect the resistance between the base of the coil packs and the chassis,

has it still got the stock J pipe restriction? (this limits fuel flow to maintain a basic fuel pressure on the return hose incase the reg fails)

not discounting from what jdub said but there is 3 things it could be

electrical related = follow the TSRM and measure resistance of electronic components as specified
fuel related = get a fuel pressure gauge on there, maybe try a different reg
compression related = do a comp test to rule out mechanical failure, also its very likely it could be a boost leak, i know you tested it for leaks but you may have a blow inlet manifold gasket you cant spot.. i had perfect vacume as well,

Ummmm...the grounding wire for the coil pack plate is a field ground. It has nothing to do with the ability of the coils to fire...the ground for that is integrated into the the coil pack harness.
Take a look at the wiring diagram

He has already stated the J tube restriction is drilled out.

 

[paradox616]

Ummmm...the grounding wire for the coil pack plate is a field ground. It has nothing to do with the ability of the coils to fire...the ground for that is integrated into the the coil pack harness.
Take a look at the wiring diagram

He has already stated the J tube restriction is drilled out.

I see, missed that part about the J tube, you could be on the money with the FPR

If the grounding strap is loose/not contacting correctly i can tell you it might just get you up a slight incline... i know this from experience.

 

[jdub]

Your experience was a coincidence...I can tell you for a fact the pack plate is not required for the coils to fire. I proved that for over a year when I 1st got the car.

Take a look at the wiring diagram for the ECU to the coils...I'm not making this up. I'm also not saying it shouldn't be there...a field ground is important. The coils will work fine without it though.

 

[williamb82]

well didnt bother checking plugs. pulled apart the 2 burnt ecus and the "good" ecu. all have the same resistor fried. seems something is amiss in the engine harness itself. we are gonna strip it down and check it all out. but likely just fix the 88 harness i have and swap to the 88 harness and ecu. that should fix it.