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SE Texas Member
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Discussion Starter · #1 ·
This post's a little long but hopefully it will give you guys some background info so you can help if you can. Thanks in advance guys!

I have a '94gt with 60k on DOHC motor. I've replaced the timing belt, all 3 timing belt covers, tensioner, pump, plugs, wires and crank angle sensor. Then a rag got caught on the rear cam gear and broke the cam angle sensor, so I had to replace it also. After installing all the new parts she started on the first turn. I killed it and restarted and she ran great until the motor started getting warm, then it started to miss, so I killed it, rechecked all the wires, hoses and water, but all looked good, so I restarted. As she got to operating temperature she started missing badly, then died and would not restart. I could smell gas so I checked the spark and I was only getting fire to 2 plugs (2&5). I thought the timing jumped so pulled her back apart and rechecked the timing and all the marks were right on the money. I figured it had to be the Power TR Unit! So I bought one from mykiss69(very cool guy) and he sent 2 units to me. No luck, tried both, still only getting spark to 2 & 5. I checked the diagnosis code and got code 23: TDC sensor (Which is the cam angle sensor). I thought that there was no way a new part could be bad, so I checked the volts at the harness connector: 12 volts, 5 volts, and ground. So I took the motor back apart and had them replace the cam sensor. I installed the new cam sensor and she started first try, then the same as above happened. I let her sit overnight and tried it again. I was back to only getting spark on 2 & 5.

Thanks for reading and anything you guys can think of will be appreciated.
Elliot
 

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Good description / info.

Problem appears to be somewhat related to either temperature/ heat or the amount of time that the engine/electronics are on.

Bad ECU's have been known to cause some pretty bizzar symptoms - seems odd to have one flake out just as you are getting your engine back together but that's Murphy's Law.

Might be worth inspecting the ECU for any leaky capacitors and/or try a swap with a fellow member.


Clint
 

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Discussion Starter · #3 ·
Clint, appreciate your post, I was thinking along the same lines you are, read that if the temperature sensor goes bad, the car will die or not start and should give a code 21.
Even after taking the cables off the battery for 30mins and checking the code after retrying to start the car, still only getting one code: 23.

Did some reading on ECU's and most of the guys that had bad symptoms, had ECU's made before '94 But did take the ECU out and looked on both sides of the board but couldn't see any capacitors that looked bad or any marks on the board, which looked new. The bad is, don't know any guys in the Beaumont area.

As for the amount of time that the engine/electronics are on, Thanks, because I didn't think of that.
So started thinking maybe the rag bent the cam sensor plate, which might be rubbing the cam angle sensor and killing it. I'm almost sure the sensor is not suppose to touch the plate. If someone knows it suppose to touch, please post. If not, that means taking the motor back apart again and making sure the sensor plate is ok.
But was hoping maybe, before I open her back up Friday, a few of you or a lot of you guys could think of something I might try or check first.
Thanks guys
Elliot
 

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noruleZ

Re-read the post - first time I mnissed the fact that the only way you got it to start was by replacing the angle sensor - I should have asked if there was any mechanical damage to the sensor.

Sensor not supposed to touch anything - it is a non-contact sensor. If it was touching it is because the plate got bent.

I feel your pain.


Clint
 

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Discussion Starter · #5 ·
Ths sensor was broke open when the rag was grabed by the plate or cam gear and was pushed into the sensor by the plate while I was turning the crank to set TDC.
The rag was suppose to keep items from getting into the motor while the intake was off.
heh, to keep the motor safe.

Thanks for the info. Will post back after I check the sensor plate.
 

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Clarification before you open it up again.

Original sensor damaged because of rag
First replacement sensor (only worked for a short while)
Second replacement sensor (only worked for a short while)

My question - Was there any mechanical damage to the first replacement sensor?


Clint
 

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Discussion Starter · #7 ·
Your summation of the situation is correct. The motor will only run after a new cam angle sensor is installed and after each replacement the motor will only run for a short time.

I did look to make sure the (first) replacement sensor was not broken or cracked when I removed it, but I'm not sure if there was any rubbing on the two prongs that the plate runs through.

Elliot
 

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Discussion Starter · #8 ·
I took the motor back down today and the cam angle sensor was rubbing on the sensor plate. I reset the plate and now I'm waiting for another sensor. Hopefuly this is what was killing the sensors.

Thanks again for your help,
Elliot
 

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Advise is easy - you did all the work. Glad you got your wheels running again.


Clint
 

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Dug this one up from the grave. I am having a similiar problem. Spark only on 2 & 5......I have replaced ECU, coils, transistor.....EVERYTHING!! could this be my problem?? Even though I have no bad Code??
 

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Discussion Starter · #12 ·
From what I have found while repairing my car if the cam angle sensor has gone bad, then you will lose spark on two cylinders.
If it is the crank angle sensor that is bad, you will lose gas and spark.

First check to see if you're getting gas. If not, it could be the crank angle sensor which can kill the gas and spark.

If you're getting gas, check the volts going to the coils. If the coil is getting volts, unplug the cam angle sensor and check to see if it has voltage going to it. If it does, than there's a good chance your cam angle sensor is bad.

If you're not getting voltage to the coils, cam angle sensor, or crank angle sensor, it could be your ECU or your fuse for the ECU that is bad.
Some guys had alot of problems with ECU's on pre 1994 cars.

Also, on the code, if you have at anytime pulled a battery cable off, then the codes were cleared. Make sure your battery is at full charge and try starting the car again and then check the codes.

Hope this helps,
noruleZ
 

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Q1 - What changed just before you began having this problem?

Q2 - Have you tried measuring end-end resistance of spark plug wires 1<->4 and 3<->6 and compare them to 2<->5?


Clint
 

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I am checking spark at the coils....And only getting spark on 5 & 2 cyls.

The ECU is rebuilt.....
The coils have been swapped and are getting power.
Plenty of fuel....Smells.
The Transistor has been swapped and tested according to S.M.
My question is that did you only obtain spark on 5 &2 when your CAS went?
 

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Let me clarify CAS ...Cam Angle not Crank
I am going to Test the Cam sensor at the computer this weekend.
If anyone has a spare Cam Sensor they will sell cheap let me know. 300 for the computer and 50 for the transistor and 40 for the coils.....It adds up to quick!!!
Thanks
 

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I cannot get a code to come back...Well, I cannot get the CEL to stay on...When the car died...If ran untill warm and then the CEL came on and bogged and died.
I unhooked the battery to charge and cannot get the code to return. The code is different for a 93 comp. to your 94.
 

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Sorry... I am a little confused... please clarify

Are you trying to test high voltage spark at coils with no spark plug wires attached? (Both spark plugs need to be attached and grounded to properly test for spark.)


Clint
 

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OMT - Are the symtoms identical with both ECU's?

Note: ECU's have common failure modes so there is some risk that replacing your bad ECU with a used ECU may not solve the problem. (None of the ECU repair shops can guarantee that the ECU is functioning 100%, however, the better shops will provide a replacement warranty.)

I would not rule out the possibility of a bad ECU until you have seen the ECU run correctly on another car. (I would offer to test one of yours but mine is RT/TT)

Note: There is a guy with screen name EP looking for bad ECU's to try out on a new test fixture. What makes his test unique is that it simulates a running engine.

http://www.3si.org/portal/forums/showthread.php?threadid=134990&goto=newpost


Clint
 

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I have tested both ways.....Basically I get no spark on cylinders 1, 3, 6, 4.........
Only on 2 & 6 does spark occur. When I test at the coils I put a screwdriver into the coil and ground against the motor lift point. I only spark on 5 & 2.
 

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Would you mind doing the following test?

1. Attach two spark plugs wires onto the same coil (1/4) (You could borrow the wires from 1+2 for a quick test without even removing existing spark plugs.)

2. Measure resistance between two wires (which includes all conections and the secondary of the coil.)

3. Install two spark plugs and have both spark plugs leaning on metal of engine.

4. Test for spark.



Clint
 
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