7mgte starts, runs rough, then stalls

[DylanB]

Good afternoon everyone. New to the forum and have a question. First off I've tried searching but every time I try it comes up with a blank page with the SM logo at the top. I have a 88 MKIII with a JDM 7mgte, basically stock. I blew a head gasket the day after I bought it, or it was blown before and I was unaware. I replaced the head gasket with one from the local parts store (didn't have the time or the money for metal gasket and machining). I purchased ARP head studs and torqued them to 85ft-lbs, I had the head machined flat (it was .009" warped). Lapped in the valves. Compression was good on all cylinders with number 6 being the worst with 40% leakage. All others were under 10%. I replaced the starter, and battery as well.

After I finished everything it started right up. I let it idle and it ran fine no issues. So I went and purchased an Autometer oil pressure and coolant temp gauges. Oil pressure is good when its warm (looks to be about 5-7 lbs) Coolant temp is a little cool (runs around 180* with new thermostat). After I did all this I drove it about 35 miles and it drove good, stayed out of boost as best I could. Anyway the next day I started it up and let it idle for a minute, and then out of the blue it started to misfire terribly, I revved it up and it ran smooth at 2000RPM but when I let off, it stalled and reeked of fuel. I couldn't get it to start for a few days after that. I had to go get the battery charged at oreilly's from trying to start it, and when I put it back in it started right up, with the same symptoms, starts, runs fine, and then misfires and stalls. I haven't driven it under load since this has been happening, so I cant comment on how it runs under load yet.

Im at a loss, Im trying to figure out why it will run fine and then randomly stall (sometimes 2 minutes, sometimes 5). Cam sensor wiring is good and tight. All electrical connections that I have checked are making good contact.

If anyone has any ideas I would be grateful.

 

[radiod]

Can you tell whether it's gas or oil coming out in smoke? If it's gas you either have a problem with spark or injection (obviously), if it's oil, you've got other issues. Were the valve seals looked at or changed when you did the work?

 

[DylanB]

Can you tell whether it's gas or oil coming out in smoke? If it's gas you either have a problem with spark or injection (obviously), if it's oil, you've got other issues. Were the valve seals looked at or changed when you did the work?

There isn't any blue smoke out of the exhaust, just a significant unburned fuel smell, the valve guides were inspected by the machine shop and he said they looked fine. They also inspected the head for any cracks. I was leaning towards the CPS but I was confused about why it would run fine and then mis suddenly. I was also thinking O2 sensor, maybe the ecu is getting signal from the o2 sensor and pouring extra fuel in? Is that a logical conclusion to make? AFM is plugged in and clean, no vacuum leaks that I can tell. My spark tester broke so I need to replace it with another one.

I dont have access to any noid lights right now I've been looking for a good set to buy for my personal box. I am assuming that I am getting fuel as the exhaust smells like it. I dont like to assume but at this time Im afraid I have to.

Thank you for the response, any help is greatly appreciated.

 

[IndigoMKII]

Well, if you could get it to run long enough you could start pulling plug wires one at a time. When you don't get a change in how it acts, there's your bad cylinder, then you need to figure out if it's spark/fuel.

 

[DylanB]

Well, if you could get it to run long enough you could start pulling plug wires one at a time. When you don't get a change in how it acts, there's your bad cylinder, then you need to figure out if it's spark/fuel.

Im gonna try that today, I hope I have enough time when it starts to mis and before it dies to at least do a few cylinders. Ill report back later today. Thanks everyone.

 

[DylanB]

So I started it up and it ran smooth, right at 1100 which is about right on cold start in 35* weather, idled fine for about 2 minutes and then started missing. I pulled the number one plug wire off the plug and i couldn't tell a noticeable difference in engine rpm, but it was fluctuating up and down at this time. I went to pull number 6 (cylinder 1 had leakage prior to tear down. I had the machine shop clean up the seats a little and when I lapped them in, there was less than 5% leakage) Cylinder number 6 had around 40%. As I was about to pull it off, it stalled. I went over and started it back up and it was idling around 3-400 RPM, by the time I got to the other side to pull the wire off it stalled again. I cant get it started now. After it stalled this last time I had intermittent tach signal while cranking, it would catch like its going to start but wouldn't. Ill try to start it again in a few hours or so.

I also noticed that the fuel smell I originally mentioned wasn't there. Exhaust smells normal, not sweet or like unburned fuel or oil.

I double checked the connections at the CPS, AFM, ICM, TPS. All were good and tight.

 

[IndigoMKII]

Could we get a video while you're doing this? Have you double checked your mechanical timing as well?

 

[DylanB]

I will try to get a video if it starts up later today. I haven't double checked the mechanical timing, simply because I would think that it would misfire all the time, not just after 2 minutes of running. Im not getting any backfiring or popping out of the exhaust and i can rev it (only went up to 2000) If It starts later today I will get a video, if not I will try tomorrow morning

 

[DylanB]

Below is a video I took a few minutes ago. It was missing pretty bad, you can hear it as I rev it up. I stopped the video and went and popped the hood, and by the time I got the hood open it died.

http://www.youtube.com/watch?v=vJLz6vgXTTE&feature=youtu.be

After it died I took this video of me trying to start it. So you can see the intermittent tach signal. I will try to get a video of it running smoothly then missing, and as I pull the plug wires off tomorrow, I dont think it will restart today.

http://www.youtube.com/watch?v=LB_S...xt=C331839aUDOEgsToPDskLaJwbeKiopj2-sgmp3GPUS

Fuel might be bad Im not sure, I hate to go put more gas in it just to let it sit until I figure it out.

 

[radiod]

How are the wires to the coil packs?

 

[DylanB]

How are the wires to the coil packs?

Coils tested good, and the wires to the coils ohmed out good, 12 volts at the connectors to the coils. replaced the spark plugs and the misfire got worse

 

[IndigoMKII]

Did you gap them properly? All plug wires good?

 

[DylanB]

Little more info, I was being rushed before. Coils had .2-.4 ohms at the connector, wires leading to the coil ohmed out at .1 each. 12v at each coil. I wasn't able to ohm out the flush wires because my stupid meter probe was to short to reach the contact point on the wire. Plugs were gapped at .032" I had autolites in it before. The parts store said that "I should put champion coppers in because they were the next best thing to NGK's" I was getting read to test my ICM when I got called away.

Side note. My valve covers were a little lose so they leaked oil down in the plug galley. When I pulled the plug boot off the plug it was covered in oil. I've got as much as I could out but there is still traces of oil in the galley. Any chance that oil could be on the threads and causing excessive resistance on the ground side of the circuit?

 

[DylanB]

Just pulled the number one plug out and it is black as night. They've only been run a minute or 2 at best, so am I looking at a AFM? or O2 sensor?

 

[IndigoMKII]

The car will still run without both the AFM and O2 sensor, you just can't rev the engine at all with a bad AFM. Did you try cranking the car with number 1 plug out and grounded it to see if it's firing?

 

[D7MSupra]

When my tach lost signal like this it ended up being a problem in the fusebox next to the clutch pedal.. no blown fuse but a short.. Ever since I put a shim between the fusebox and whatever is on the other side Ive had a good signal.. My car didnt have a miss like that tho

 

[DylanB]

The car will still run without both the AFM and O2 sensor, you just can't rev the engine at all with a bad AFM. Did you try cranking the car with number 1 plug out and grounded it to see if it's firing?

I did several tests, the last test I did was the igniter test in the ICM, using 3v check for momentary ground at the coil connectors, I didn't have that. I checked all the fuses with a test light on both sides. I believe it is the ICM. I called several junk yards for one and no one has any supras tho. Hopefully I can find one cheaper than 400 at oreilly's.

 

[DylanB]

When my tach lost signal like this it ended up being a problem in the fusebox next to the clutch pedal.. no blown fuse but a short.. Ever since I put a shim between the fusebox and whatever is on the other side Ive had a good signal.. My car didnt have a miss like that tho

When I saw the tach losing signal I initially thought the CPS was bad, but I did the CPS test per the TSRM and it passed. Im thinkin that if the CPS triggers the ICM but the ICM doesn't fire, maybe the ECU doesn't see a RPM signal? If that makes sense. Im not real sure about the networking on these, Im fairly new to Supras. I do appreciate all the help you guys have given me.

 

[JStoked]

I know it a stupid? But whats you cel light doing? Are you able to get any codes?

 

[jetjock]

^ Finally. Only took 18 posts.

OP: It's not your igniter...