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Discussion Starter #1 (Edited)
Alright so I recently rebuilt the top-end of my 7M-GTE for my 87 Supra. Although it seems to have consistent issues with rough idle and acceleration. It seems to run great when the ECU is reset and the engine is cold, as it heats up the idle gets rough and acceleration gets choppy and cuts out in a consistent rythm especially if I hold it at WOT. Although it could cutout at nearly any RPM and throttle depending on the situation. Its not boost cut and I dont have codes. Also vari The longer the car runs the worse it gets, most of the time.

I really can't figure out the issue even though I have done a slew of testing. I have gone ahead and replaced the TPS, O2 Sensor, and AFM and each time it seems to be the solution until a couple minutes later of running then the issue comes back. I verified operation of the IACV and clicks. Even ran through voltages and resistance of each pin to the ECU to see if there were any sensors or wires were out of spec. I have also adjusted CPS and aligned everything and then timed it 10 degrees after jumping wires in the diagnostics box. Also did a boost leak test, IC hoses are good.

The first part of the video is of me cruising through my neighborhood at varying amount of throttle and speed. Second part of the video is just idling, it almost idles like this 90% of the time after getting hot. Any leads would be of help, thanks.

Edit: When it rough idles, the exhaust smells rich. Also don't worry about the oil pressure gauge, verified oil pressure, working on getting a replacement gauge.

 

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At idle, it sounds like it is missing on 2 cylnders. Have you verifed that all cylinders are getting spark???

You replaced the TPS but did you make sure that you adjusted it per the TSRM for your model year?

As an example, For the 89 Supra.


Notice the gaps and resistance value. You should follow that to the T otherwise you will have that issue.

Also word to the wise, not to smart to WOT the car while in that condition, if it is due to a lean condition, you are going to pop the motor.
 

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Discussion Starter #3
Thanks for the response figgie,

I will go over the spark plugs again and verify spark. I followed the 87 TSRM for my Supra and paid attention to the gaps and resistance values, everything is in spec. Also I take you up on your advise, I won't even drive it around anymore till I can figure out this issue.

I got some new information to add in here that might actually lead to the problem. I was overlooking the vacuum lines to double check and make sure I had no leaks. I moved the EGR VSV and the engine instantly died. Nothing got unplugged, just died. I restarted the car and kind of moved it around and the idle change sporadically... I'm not quite familiar how that could be but I pulled the EGR VSV and followed the TSRM for testing it. No resistance value, no continuity on its pins, its probably dead.

While I was at it, I pulled the VPR VSV and tested it as well. It did have continuity but its resistance is ≈ 300ohms, which is about 250 over spec. Come the weekend I'll test the fuel pressure and see if I can get any more information, but is it possible that these two VSVs could cause these issues? I understand the VPR VSV lowers fuel pressure at idle, but I'm not to familiar with how the EGR VSV functions. Thanks.
 

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They way it cuts out suddenly sounds like a bad electrical connection or ground affecting injection or ignition. Certainly faulty CPS wiring or incorrect gap could lead to a problem like that. You could monitor The CPS signals and IGT signal with a scope. If they cut out, when the engine cuts, you don't need to look at anything else. Honestly, I don't hear a misfire at idle. Any codes?
 

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Discussion Starter #5
No codes, which is inconvenient cause I have no leads to go off of. I don't have an oscilloscope to scope out the IGT or CPS signals, but I'll look over their connections.
 

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well if you have reliable spark then those signals are good. even an inductive pickup timing gun on the plug 6 wire will tell you that. if the gun stops blinking the same instant it stalls you have an ignition problem. possible to reproduce without driving? or do you have a timing gun that can reach the passenger seat for a friend to watch?
 

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Discussion Starter #8
Thanks for the advice, so I noticed that the engine is starting to run rough in general now. So I hooked a timing light up to plug six like suggested, it sparked when cranking and kept for a second or two after starting then completely lost spark on plug 6 and the idle sounded really bad. Definitely missing 2 or more cylinders. Figured I'd check the packs next so I removed them and I noticed hair line cracks on all the packs. Some worse than others, but all 3 had cracks. Are these bad enough to be loosing spark?
 

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well you have an ignition problem, somewhere between the cps and the spark plug, but I wouldn't skip the diagnostics. Plug wires primary coil resistances, grounds, primary voltage, ignitor tests. I prefer to work with sound hardware to start. You can still order brand new coils made by the oem supplier, i think through Rock Auto. I replaced mine for peace of mind, also found brand new coil pack connectors, and added an extra ground to my coil pack and ignitor. also new plugs and wires. all this is just preliminaries updating 30 year old electrical. I talked to a guy who said you can test ignition nicely by removing the cps from the head and just spinning it by hand to trigger spark. Very convenient. Also check wiring and ecu ground. If you get through all that and problem not solved then i would turn to a scope next. Good luck.
 

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Discussion Starter #10
Yea that CPS trick really was useful when I first was trying to get this car started at the end of last year. Speaking of the ECU ground, when I was testing the coil packs a few hours ago I got code 11, which I haven't seen before. I checked the ECU ground and it was slightly loose. I was looking at the VSV near it and must've bumped it which cause the ECU to lose ground and the engine to shut off. I thought it was the VSV that caused that but that doesn't make sense for the VSV to cause the car shut off, but the ECU ground would definitely do that. i tightened it and the car has been running and idling great. I haven't driven it yet as I'm doing some other things on it right now, but that might have been my issue. Ill give an update after I'm done covering some other things on the car.
 

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Discussion Starter #12
It appears to have fixed the issue, but unfortunately the engine developed a really bad knock during the test drive today. So its probably ruined at this point. I'll be tearing it apart soon to evaluate the damage and look at my options.
 

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Curiouser and curioser. Wiser folks than me will have to weigh in on weather the ignition problems were related. On the positive side, it was probably needed if the car is basically stock. It used to be, just replace the head gasket and you'd be ok for a while. Now, you really can't own a stock MK3 for long without having to tear down the engine at least once. If you build it well and don't get too crazy tuning it, it should be reliable when you are done. I found so many levels of crap rebuilding my car the first time, then rebuilt it again due to overlooking a rebuild on the turbo ( oil seal.... ). Between wiring, connectors, rubber parts cracking, rust, etc., at 30 years you are just asking for a string of endless headaches if you don't tear the whole thing down and carefully go over everything as you put it back together. For the professional mechanics here, not a big deal, for amateurs like me, it was a huge learning curve searching forums and asking dumb questions from busy, smart people, but so worth it in the end.
 
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