Spyder Stuttering/Skip/Misfire

[Furiyous]

So, I have been trying to figure out the issue with my car for the last couple months (1997 GS-T Spyder). For some reason, after i start the car anywhere between 5-20 minutes (its random) it starts to skip/stutter like it has a slight misfire of some sort. The longer its running, the more it will start to misfire and skip. It has never stalled because of it though.

When initially start the car from a cold start, it runs PERFECTLY, no skip, no issues. After usually about 10 mins or so of driving/idling and the car warming up, it starts doing this, at idle, acceleration, doesn't matter. Its almost like a random irregular heart beat at idle in a split second.

Things I have done so far:

- 4 new Spark Plugs, NGK, with proper gap (0.28-0.31)
- 4 new Denso Spark plug wires
- New ICM/PTU, original Mitsubishi part
- 2 new Delphi coils installed as well
- New upstream Denso O2 sensor (was insane to get this thing out of the manifold from how stuck it was)

I will say it has been much better with those things replaced but its still there, especially on acceleration. Even very light acceleration it will skip badly. I do not know what else to check for. My OBD tool won't recognize the car for some reason (i think the car is too old for my ThinkDiag scan tool) so I cannot tell which cylinder is misfiring. I did check the cigarette lighter fuse, and its good (this controls OBD II power/communication I guess from what I have read).

From what I have researched, could possibly be injectors, injector resistor pack, ECT Sensor, Cam/Crank Position Sensors, vacuum leak or worst case the ECU. Engine Temperature gauge goes up to normal operation and stays there right below the halfway point so I am not sure its the ECT Sensor.

There is NO CEL that comes on at all, even when it skips, so I have no clue where else to look. I even unplugged the upstream O2 sensor to keep the car in open loop and still occurs. Any ideas would be helpful. My dad is going to try to bring his scan tool from work to check and see if it will communicate with the car so I can get a reading on the misfires hopefully some time this week.

Anything I miss? Should I check anything else while I wait for a scan tool?

Thanks for any input.

 

[dwb]

Do you see the CEL for a few seconds after turning on the ignition? Maybe there's a code stored you haven't noticed, so definitely check for that when you get a working scantool.
How are your electrical grounds? Starter bolt, firewall, intake manifold, and neg battery post grounds should be tight and clean.

 

[Furiyous]

Haven't checked the grounds yet, but will do that. I did also replace both the terminals for the battery connections as they were all corroded and worn out. I do not recall seeing the check engine light come on at the start, ill keep an eye on that. I did see it come on when i disconnected the O2 sensor so i know the light is working.

I am more concerned that it has no communication from the OBD II. I noticed a lot of threads on here for that happening for multiple reasons. Is there another fuse besides the footwell cigarette lighter that can cause communication issues with OBD II port in case I have the same issue with another scan tool?

 

[chrysler kid]

Sounds like a fuel pump issue to me, you might want to hook up a fuel pressure test gauge (or buy a cheap fuel pressure gauge pod gauge) and watch to make sure the pump is throwing a steady 39 to 43 psi

 

[luv2rallye]

Is there another fuse besides the footwell cigarette lighter that can cause communication issues with OBD II port in case I have the same issue with another scan tool?

Yes. The kick panel 10 amp Door Lock fuse (middle row 2nd from right) which provides power to the OBD pin 16 connector.

Your starting problem sounds like the classic "Hot start" (aka vapor lock) problem. Usually it's the fuel pressure solenoid (https://www.dsmtuners.com/threads/vapor-lock-hot-start.217349/#post-1821514). It's on the firewall between the brake fluid reservoir and the clutch reservoir.