Car died.....Little direction please

[rdomeck]

Last week my car was shutting off when hitting a bump. This happened 2-3 times in about 10 miles. Didn't happen the next day, but decided to drive something else out of town for a long weekend. Drove the car again Monday and the problem was there about a 50 times in 4 miles. Got it back to my shop and drove one of my trucks. Took the panel down to expose the main relay by the ecu. Checked some wiring under the hood. Pulled the panel down below the steering wheel and checked some wiring there. When it happens you can hear the relay shut off and the tach drops to 0. Kind of like you shutting the key off.

Any obvious places to look? Are the main relay's known to go bad? Battery has been moved to trunk. I also checked my connections there! Thanks for any help you can provide.

 

[toybreaker]

Does the tach drop offline immediatelywhen this problem first manifests itself or is there a delay?


One place to look when you hear the mpi relay shutting down is the cas harness/connector.

The harness at the cas is subject to heat and vibration and is often problematical.

The ecu uses the cas signal to "authorise" the fuel pump to run.

no cas signal = no signal from the ecu to the mpi relay to run the pump.

 

[rdomeck]

Thanks, I'll look their tomorrow. At least it quit completely. Much easier to find a problem when it is there all the time instead of sometimes!

 

[rdomeck]

Ok I have fuel but no spark. I can hear my MPI relay click on while cranking, but when I stop cranking it shuts off. I have unplugged and plugged my CAS a couple of times as well as a few other's. Anybody know of a good way to test my CAS? Looked in the library and tech articles, but didn't find anything!

 

[fuel]

MPI clicking off after ceasing to crank over is normal - you don't want fuel circulating when the engine isn't running for safety reasons.

Are you getting a check engine light? I would say it would be a connection somewhere to the CAS or perhaps the MPI relay itself. I would try remove the MPI relay from its mounting and let it sit free from vibration (perhaps same with the ECU) and see if it still happens.

 

[ghostinthevr4]

To check the CAM angle sensor you need to unplug it and check for continuity at pin 4 I believe. One of the pins in between should have 3.5-5 volts if I remember correctly. Do this on the harness not the CAM sensor.

 

[mitsuturbo]

Quoting rdomeck:
Ok I have fuel but no spark. I can hear my MPI relay click on while cranking, but when I stop cranking it shuts off. I have unplugged and plugged my CAS a couple of times as well as a few other's. Anybody know of a good way to test my CAS? Looked in the library and tech articles, but didn't find anything!



Fuel, no spark?

Check Coilpack and PowerTR unit also.

The way i've always checked the spark system is to just unbolt the CAS and spin it by hand. You'll hear injectors firing and such if the CAS is working and the ignition is in KOEO state. Of course, if you're going to do much with it, unplug the resistor pack as well, so the injectors wont fire fuel into the cylinders as you spin the CAS. This is beneficial in the sense that you're not killing the battery and starter by cranking the thing over and over and over. Makes it easy to diagnose CAS, Relay, ECU, Injectors, Coilpack, or PowerTR unit, especially if you have spares of these parts lying around like I do. If i'm not mistaken, turning the CAS by hand also makes the fuel pump run. No big deal so long as the injectors aren't firing a bunch of fuel into the cylinders.

Also, i had a similar problem to what you've described once. My turbo timer harness connection wasn't very tight when i got one of my cars. I was driving down the highway, hit a bump, and everything would blink off for a moment. Drove me nuts, but at least it was a quick/easy fix.

 

[rdomeck]

How easy is the turbo timer harness to get to? I did check a little today and I am not getting a CEL and I can not connect to the ECU. World the factory alarm have anything to do with this? Thanks for the help so far!

 

[desant78]

Quoting mitsuturbo:
Quoting rdomeck:
Ok I have fuel but no spark. I can hear my MPI relay click on while cranking, but when I stop cranking it shuts off. I have unplugged and plugged my CAS a couple of times as well as a few other's. Anybody know of a good way to test my CAS? Looked in the library and tech articles, but didn't find anything!



Fuel, no spark?

Check Coilpack and PowerTR unit also.

The way i've always checked the spark system is to just unbolt the CAS and spin it by hand. You'll hear injectors firing and such if the CAS is working and the ignition is in KOEO state. Of course, if you're going to do much with it, unplug the resistor pack as well, so the injectors wont fire fuel into the cylinders as you spin the CAS. This is beneficial in the sense that you're not killing the battery and starter by cranking the thing over and over and over. Makes it easy to diagnose CAS, Relay, ECU, Injectors, Coilpack, or PowerTR unit, especially if you have spares of these parts lying around like I do. If i'm not mistaken, turning the CAS by hand also makes the fuel pump run. No big deal so long as the injectors aren't firing a bunch of fuel into the cylinders.

Also, i had a similar problem to what you've described once. My turbo timer harness connection wasn't very tight when i got one of my cars. I was driving down the highway, hit a bump, and everything would blink off for a moment. Drove me nuts, but at least it was a quick/easy fix.



+1 car would turn, got fuel, but no spark. Coil pack and power.transistor i changed at the same time and it worked.

 

[mitsuturbo]

NO, the factory alarm doesn't do sh*t as far as the ECU is concerned.

 

[rdomeck]

Alright. My CEL is not on and I can not connect to link. Seems like something other than a faulty sensor? Sounds like I am not getting power to the ECU and I don't see a CAS or a power transistor causing that! Were would I find the turbo timer harness? And does that cut power from the ECU? Fuse in engine bay is good BTW. This seems like an electrical connection rather than a sensor because it was intermittent when it started having problems......

 

[mitsuturbo]

Does the car HAVE a turbo timer? If so, check the wiring from the ignition switch under the steering column and to the right (near the duct work, and radio behind the driver kick panel). There should be a couple six pin connectors there. Make sure they're tight/snug.

It's entirely possible that your main relay took a crap. I've seen it happen. I also had one with a flaky connection because some dingus wired a fuel pump wrong and caused things to MELT a little bit.

Make sure the ECU is all plugged in properly. Inability to connect to DSMlink is a definite sign something's very wrong. Does the CEL come on when the ignition is on all the way? It should. Can you turn on other things in the car? Radio? Does the seatbelt function when you have the key on all the way and shut/open the door? Has the car ever had a SAFC installed? Is the wiring to the ECU in good shape?

 

[rdomeck]

The car does not have a turbo timer...Just seemed like a place to check were that might plug in. The wiring is in good shape with the car. It only has 100,000 miles on it and has had good owners that didn't hack up any wiring. I'll check my connections again at the steering column and I'll pull the ecu down to make sure all the plugs are seating well. The CEL never comes on. Everything else with the car works. Radio, seat belt's, etc. Were can locate the main relay?

 

[rdomeck]

^Meaning other than the one by the ECU?

 

[mitsuturbo]

The main MPI relay is near the ECU. They DO go out. More so on the 3/S cars, but they do go out on DSMs as well, from time to time.

If you CEL *never* comes on, even with KOEO, then the ECU is not working. Plain and simple. Check EVERY fuse.

Have you tried pulling the ECU and checking the connections for the EPROM/Link? Maybe something's not right there...

 

[rdomeck]

Well....I am an idiot some times! The first thing I should have checked and thought that I did was the fuse in the engine compartment. It was blown. I put a 30 amp in place of the 20 amp and it did just fine......Until I went to take it for a test drive and it blew that fuse also! Now I get to spend a year tracing down this problem. It's fast when it's running!

 

[Terrance362]

Did it blow after a couple minutes? Did u rev it and then blew? Have I been checking grounds?

 

[rdomeck]

Reved and it blew...Put a new one in and I have driven 100 miles without it doing anything! Looks like all original fuses and I'm wondering if the originals have a habit of having cold solder joints? Took a blown one apart and see that they are made up of three pieces that are soldered together. I can see that over 20 years these solder joints are likely to fail. The new ones I have are one piece design....Guess I'll see how things go.

Looks like from the wiring diagram this fuse runs power to the MAF and a couple other things.

Would it be likely that the GM MAF pulls a little bit more current than the stock?