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Discussion Starter #1
Hey everyone, I'm new to the site here and I just recently bought a 93 Stealth ES. Since owning it and replacing some parts (fuel filter, plugs and wires, valve cover gaskets, IAC Sensor, etc.) I've had this problem where I'll be driving and the car will run perfectly fine from starting up until about being completely warm or after driving so long where the exhaust changes tone and the car just kind of doesnt want to move when I put my foot down on it.. any idea what would be the cause of the problem? My guess was ignition coils and intake air control and it did help fix it a little but I'm still struggling with it.
 

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hmmm, I would almost put money on the fuel pump - it is common as they age and start to die, they tend to show symptoms the most after they have been running awhile/get hot.

Also make sure the car is still showing at least 12V on the volt gauge once its fully warmed up. It should start at around 14.7V When cold/first started and slowly drop to the 12's. Undervoltage can cause all kinds of issues.

My guess with the change in engine tone is the engine is suddenly being run under greater load trying to make up lack of sufficient fuel delivery, which would cause lack of power as well...

Something else to look into would be to open up your ECU And check for any exploaded/leaking capacitors and or damage to the circuits. That is a common thing on old Mitsubishi that can cause some of the hardest to diagnose, and completely odd ball issues.

I.E. I had a 1992 Laser RS Turbo with a bad ECU that the previous owner figured out it would only semi run normally if you stuck a piece of duct tape over a portion of the inlet for the MAF. The cause was leaking capacitors, new ECU and the car ran fantastic after that.

Another thing to check would be just make sure you don't have a rip in your intake boot, and the hose clamps are tight, also make sure the CAS adjustment nut is tightened down correctly, if it was left loose, vibrations will make it wonder around reducing and increasing timing, I doubt that's it but worth checking.
 

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Update: I ordered an ECU but the issue is I believe it's bad, I try to turn over the car with it and it barely cranks. I put the old ECU back in the car and ordered a PTU, between the time of the last posting and now the car ended up running on just 2 cylinders and now it's running at 5 with only one coil pack not running properly for whatever reason, the middle pack is only getting spark from one side.
 

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I am pretty sure the PTU can fail to send spark signal to an entire coil pack, not half of one. So if only half of the coil pack is firing, it would have the to be coil pack itself? Any CEL? When my PTU went out i got a CEL whenever a coil was not firing (although the CEL went away whenever the PTU intermittently resumed normal operation)
 

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Discussion Starter #5
I am pretty sure the PTU can fail to send spark signal to an entire coil pack, not half of one. So if only half of the coil pack is firing, it would have the to be coil pack itself? Any CEL? When my PTU went out i got a CEL whenever a coil was not firing (although the CEL went away whenever the PTU intermittently resumed normal operation)

The car is running off of 5 cylinders with the new PTU installed, the old one caused it to only fire with 2, I have no CEL, I could try and get a new coil pack and see if it's just the pack itself, progress has been made things just need a little bit of TLC.
 

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You can also try switching 2 coil packs to confirm it is the coil pack itself - e.g., if it was the PTU (which i think is not possible in this case), the problem would not follow the coil pack.
 

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Also - confirm the wires if you havent already (switching wires on the same coil pack is fine because it is a wasted spark system)
 

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Discussion Starter #8
Also - confirm the wires if you havent already (switching wires on the same coil pack is fine because it is a wasted spark system)

Found out upon further inspection the coil pack Itself was cracked on the bottom which would definitely cause one not to spark. Ordered a new one, should be coming tomorrow. Stay posted.
 

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So concluding all my issues, the main problem was my Power Transistor Unit, when it went bad it ruined one of my brand new coil packs which caused it to crack, I replaced the ptu and the busted coil pack and now it's running back on all 6 cylinders and healthily at that. I appreciate everyone's input towards my problem.
 

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Discussion Starter #10
Here's a weird update: with all the new parts in (PTU, ignition coil packs, spark plugs, wires, fuel filter, air filter, new coolant, thermostat, and idle air control sensor) the car after its started up and warmed up wants to stumble and act like it's running like garbage- sometimes when it gets this way it looks like its burning oil when you rev it and if you stand by the exhaust it smells heavily of unburnt fuel. I've seen a lot of posts all related to this and they all seem to point to the ECU but here's the thing: I've pulled it out of the car and inspected it up and down and haven't really noticed anything out of place, I plan to eventually get a rebuilt ECU but everywhere I've looked people have had something similar but not quite like my problem. Hoping someone can come through and point me in the right direction because I'm at a loss here.
 

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...the car after its started up and warmed up wants to stumble and act like it's running like garbage...
It sounds like an issue with closed-loop operation.

-sent from my Galaxy Note 9
 

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Closed loop operation is when the ECU uses the stock O2 sensors to control fueling. It only happens when the car is warm, and under low load conditions (idle, light cruise, etc). If the car runs fine when cold, it suggests that might be a cause, since the O2s are not used on cold starts or warm up. You can read more about it by googleing and/or on stealth316.

Do you have any datalogging? You want to see what your O2s are reading. You could also see how the car behaves under WOT. If its OK on cold starts and OK on WOT (high load), that would further indicate its a closed loop fueling issue.
 

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Discussion Starter #14
Closed loop operation is when the ECU uses the stock O2 sensors to control fueling. It only happens when the car is warm, and under low load conditions (idle, light cruise, etc). If the car runs fine when cold, it suggests that might be a cause, since the O2s are not used on cold starts or warm up. You can read more about it by googleing and/or on stealth316.

Do you have any datalogging? You want to see what your O2s are reading. You could also see how the car behaves under WOT. If its OK on cold starts and OK on WOT (high load), that would further indicate its a closed loop fueling issue.
I see, would it primarily affect the upstream o2 sensors? I ordered just 2 for now since I believe the downstream sensors dont really play as big of a role in the issue, the new o2 sensors should be here in a few days so I'll update on here when they're installed.
 

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Yes, only upstream (closer to engine) are used for closed loop fuel control. Secondary (downstream) O2s are essentially to monitor your cats.
 

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Discussion Starter #16
So here's an update since the last time I've worked on the stealth: around the time everyone discussed the closed loop open loop system on the car i went and got o2 sensors and came to find out that the car only had one on the entire exhaust system. Tried to replace the old one and snapped that off in the pipe, so I drove the car without o2 sensors and on my way back from a friend of mines the car died on me right outside my place, just yesterday I looked under the hood to try and figure it out because the car cranked but didnt start, I've replaced the crank position sensor and fuel pump, and replaced the PTU for the third time. Now with the new PTU in it cranks and sounds like It wants to start up but dies out seconds later. I'm completely stumped.
 

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Did your repkacement list include fhe fuel pump? If not, when turning the key to position 2 or on but pre start, do you hear a slight hmmnnnnn. Because that sound is your fuel pump proming up. No sound, check pump.

Have yoy done a vacuum hose reduction? If not do so.

Age of clutch, friction disc, clutch fork? Amt of free play brfore engaging. Full Clutch pedal action is needed to start the car.

Is tour BISS SCRE still inserted? If gone, its like a big vacuum leak and nesses starting up.

Have you checked the ecu? Yes again, because cracked coils will throw electric arcs in least resistant direction, which a crack provides. Which can harm the ecu.

Just a FEW thoughts....welcome to the party!!! Lol!!!

Peace
 

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Did your repkacement list include fhe fuel pump? If not, when turning the key to position 2 or on but pre start, do you hear a slight hmmnnnnn. Because that sound is your fuel pump proming up. No sound, check pump.
Not exactly correct. Pump does not start until starter circuit is engaged, therefore no “hmmnnnnn” when key only turned to run position.
 

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Discussion Starter #19
Did your repkacement list include fhe fuel pump? If not, when turning the key to position 2 or on but pre start, do you hear a slight hmmnnnnn. Because that sound is your fuel pump proming up. No sound, check pump.

Have yoy done a vacuum hose reduction? If not do so.

Age of clutch, friction disc, clutch fork? Amt of free play brfore engaging. Full Clutch pedal action is needed to start the car.

Is tour BISS SCRE still inserted? If gone, its like a big vacuum leak and nesses starting up.

Have you checked the ecu? Yes again, because cracked coils will throw electric arcs in least resistant direction, which a crack provides. Which can harm the ecu.

Just a FEW thoughts....welcome to the party!!! Lol!!!

Peace
I replaced the fuel pump yesterday, put everything back in the same way I took it out, there's definitely fuel in the system because I pulled my front 3 plugs and they're soaked, I let them dry out a little. My Biss screw is still seated where it needs to be, I bought the car off someone who got it in a trade and had no idea of the condition of things but most of the car is factory still with little modifications but the clutch engages fine still. Car has 169,360 on it at the moment. Haven't done any vacuum hose reductions and I'm not sure how to go about that. As for the fuel pump I believe it primes when you turn the key to start it.
 

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Dont be surprised if the front 3 wires are a little long. Supposed to be to spec., but bith times I have bought a set the dront three are aboit .5" longer than what would ne ideal. Just means you have a lite extra bend outside the cover. DONT TRY STUFFING THEM INSIDE THE COVER PLATE. EASY TO CUT OR TEAR THE HOUSING AND GET MISFIRE. DEALERSHIP LESSON NOT OF MY DOING. SURPRISE. LOL!

PEACE
Not exactly correct. Pump does not start until starter circuit is engaged, therefore no “hmmnnnnn” when key only turned to run position.
Well then I was lied to by someone...probably a dealership or private shop, lol!

And my bad. After checking it was my antenna motor! Lol! I thought Id dc'd the sucker when tje antenna locked up and the and the extend/retract cable broke. It is now!!! Sorry fkr the misinfo.

Peace
 
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