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[RESOLVED] Car will start cold, but won't start hot.

FilthyEvo

Well-known member
Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
O2 sensor was wired incorrectly. Grey and Black wire were switched.

I swapped in (4) 450cc injectors that all had similar resistance (2.4ohms). The car IS getting spark when the car is cold.

After swapping in the injectors, and zero-ing out the SAFC, the car fired right up and ran smoothly. Revs were smooth, idle wasn't boucning or choppy, but the idle was high. 2,000-3,000 RPM. It came down a little with the adjustment of the BISS screw.

The car idled fine, but some smoke start to come from the radiator - almost like oily finger prints were burning off, but I didn't want to chance it and shut the car off.

Once shut off, the car would NOT restart.

So, I let the car cool down for an hour. When I went back to it, it fired right up, and held idle perfectly fine. I let it run for about 20 seconds and shut it down. I wanted to see if it would restart...and it did, but it was a little tougher. I let it run for another 20-30 seconds and shut it down. It tried to start, but just kept cranking.

Now, what would cause the car not to start when the car is warmed up? Power Transistor Unit (PTU)? Would a coilpack do this?
 
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FilthyEvo

Well-known member
Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
Could it have anything to do with my Fuel Pump Relay having a bunch of gunk in it? White grease and looks a little rusty.
 

GSTwithPSI

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Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
110% positive your ECU is not seeing coolant temperature. I experienced the exact same issue with 1813. Either the sensor is sh*t, or the wiring to the sensor is sh*t. I'd bet it is probably the wiring. To test the wiring, ohm out the wires, placing one lead on the sensor plug, and the other on the ECU plug. You are checking for continuity. Is there someone in your area with a data logger? If so, that would be the easiest way to see what the ECU is seeing. If not, you can also test the sensor it like this:
attachment.php




Sensor location, right below the black plug, you can barely see it in the photo:
attachment.php


Edit: I see in your other thread that you have already replaced the sensor. You sure you got the wiring right?

Check out this thread: click
 
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FilthyEvo

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Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
How do I reach the ECU plug and the CTS plug at the same time.

This is the 3rd CTS I've put in the car since diagnosing this. The CTS tests good.

I have already rewired the wiring but maybe I need to trace it back further? Can't I eliminate the old wiring and run a new wire straight from the ECU to the CTS? This harness has already been hacked away at by the prior owners.
 

GSTwithPSI

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Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
You could run a wire from ECU to sensor, but I wouldn't recommend it. I would just peel back the harness until I found factory wiring again, and solder in a new wire from there. Dude, I went through the same BS, repairing factory wiring that was hacked by previous owners. Best thing you can do is find a spot in the factory harness to start over, and begin your repairs there. Here is a pic of 1813 when I was repairing the harness. The coolant sensor wiring is in its own little harness, so trace it back as far as you need to.
WP_000131.jpg


You need a DVOM with long leads. I put my meter on the windshield of the car, and clamp one lead on the wire at the sensor connector. Then, I take the other lead and probe the ECU pin while looking at the meter through the windshield.

Coolant temp sensor wiring:
T-pin front: Coolant temp sensor (connector B02): Green/black (crossbar of T) and yellow/green (stem of T position)

First, clamp a meter lead on the Green/black (crossbar of T, or top part of the T) wire at the sensor.

Then, you need to find pin 20 at the ECU: ECU Pinout. Put your meter lead there, and see if there is continuity between the ECU pin, and the sensor connector. If not, then your ECU is not getting a signal from you coolant temp sensor. And, I'd bet my life that it isn't getting one.

The other wire, yellow/green (stem of T position) goes to ground. It goes to the ECU sensors ground on pin 24. You can do the same thing for this circuit as you did for the other, or you could just ground it somewhere in the engine compartment. Eventually, you want to make sure it is properly grounded through the engine harness back to the ECU though.

If your car isn't seeing coolant temperature, it is screwing all kinds of sh*t up. You need to verify it is working. It would be best if you had a logger or something, that way you could hook it up and see exactly what the ECU is seeing...

Lastly, here is a link to the library where the coolant sensor wiring diagram is located. click Look on page 148 (actual document page number, not the Adobe page number)
 
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FilthyEvo

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Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
Okay, the car fired right up this morning - even in the bitter cold of 6*. It idled around 1200-1500RPM for about 5 minutes and then slowly started to climb. During this time, the car ran pretty smoothly - didn't sound like it was on 2 cylinders, nor sounded like a Subaru.

The idle went up to about 2500RPM, and I shut the car down. When I attempted to restart the car, I had no like. It just cranked and cranked and cranked.

So, I tested spark. I am getting good spark on the two outside cylinders (1&4), but very weak spark (almost non-existent) on cylinders 2&3.

This leads me to believe that the ECU, and CAS are working - as the car is getting SOME spark.

Do these signs lead to the PTU?
 

FilthyEvo

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Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
Plug Wire resistance is good. I have two sets here, and both test out good.

The connector, from the coil pack, looks like it has 2-3 wires that were brittle and cracked open. They didn't pull from the plug, but they did crack open - exposing wires. The wiring from the harness to the Coil Pack plug is fine though.

I'll have to see if I can find one local - as no one on the forums seem to have a spare.
 
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vr4play

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Joined
Feb 7, 2008
Messages
397
Location
Cincinnati, Ohio
You mentioned the fuel pump relay looked rusty. Can you here the fuel pump running when the car won't start. Usually coolant temp problems happen when cold not warm. I would make sure your getting fuel pressure and that that relay isn't getting hot and not working. It can be bypassed with a piece of wire. Did you ever try a different Power transistor. They can act funky when bad and exposed to heat.
 

FilthyEvo

Well-known member
Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
Could you post a picture of the relay your talking about? Which pins can I jump?

I used the same method on a 3000GT VR4 back in the day.

I will check/test the fuel pump tomorrow. Would a bad fuel pump housing gasket cause problems?

Just tested a known good coil pack and PTU today; no change.
 
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mcbride89

Well-known member
Joined
Dec 17, 2012
Messages
133
Location
Belmar,NJ
I know this may seem like a stretch but I have a friend with an RB25 swapped S14. he had a similar problem where the car would start fine cold abut after being ran for a little, died.

Turned out to be his CAS. Do you have a spare or access to one maybe to swap and see if that helps.
 

Diego

Well-known member
Joined
Dec 9, 2007
Messages
2,132
Location
In a van down by the river, Iowa
The coolant sender (to ECU) is my current no start problem. Link shows up a reading of -74*. Replacing that sensor soon when it gets in.
 

FilthyEvo

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Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
My logger won't be in until this week.

I will be testing the resistance of the wires from the ECU to the plug to trace down the correct wires.
 

FilthyEvo

Well-known member
Joined
Jan 2, 2014
Messages
57
Location
Barrington, NH
Changed the plugs this morning, tied up any loose wires, and changed the oil (good thing I did).

The car seemed to turn over much nicer, and fired right up. It wanted to die a little bit, but still ran well. Once it warmed up, the car was good to go. High idle of ~1500RPM, and I can't adjust the BISS to make the idle lower or it will want to stall.

The clutch seems to be grabbing, so I'm going to adjust that.

I checked all my fuses, and none were blown, but the tail lights and gauge cluster lights won't come on anymore...any ideas?
 
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