Car only runs with diag scanner on...PLEASE HELP!!!

Mike Manzo

Registered User
Heres the scenario. They have cut the cats off and looked at them and they are both fine. They have ruled out the exhaust system since they cant see anything else other than the cats that could clog that system.

We ran the car with the fuel cut off tripped and a gas-pump hooked to it @ 37psi, but this didnt keep it running either, so we ruled out bad gasoline.

Here are the symptoms in detail.

I have been running the car with an EEC Tuner on it controlling the fan settings and some transmission settings. The car has been running cool, but in order to keep the fan from constantly running, I do have the temps set at 197 for the low speed and 200 for the high (or maybe 210, I dont remember).

The only other mods are a cold air kit and I thought that maybe I injested some water or something, but I dont think that this is the case.

While driving the car, I noticed in the past couple days that it would be mushy off the line. Much like if you were to disconnect the MAF. Off the line it would be rather bad acceleration, but after that it seemed pretty normal with the exception of some question about the gas mileage.

Yesterday, I was driving the car home and the closer I got the my house, the worse the idle got. Acceleration was bad and the car seemed to lose power. When coming to a stop, it started to really bog out on me. When I got down the street from my house, I could put the accelerator to the floor, and the car would go nowhere. Slowly accelerating and at 2000 rpms with my foot to the floor I think I reached 20mph.

I limped the car this morning to my mechanic and he disconnected the exhaust at the manifolds and he said that it seemed to run a little better, but that could have been the release of the backpressure. He didnt run the car for long, but he did limp it over to another mechanic when it got there it finally died and would not restart.

The car cranks and cranks, but wont really catch and when it does it is only a matter of time until it dies.

While on the scanner, however when the scanner is performing its tests, the car seems to run 100%. The MOMENT the scanner is disconnected, the car dies and will not start. The mechanic is pointing fingers at the computer, but I am a little leary about that personally. Just from experience with these cars, there are ghosts that mask themselves as other problems.

One thing I noticed while the car was on the scanner was the timimg. Not being able to really read it, the timing with the car turned off was reading 10. Then when running at its best (not knowing if this was the scanner doing this or not) the timing was at 30, but I was unable to monitor it further.

This scares me because I know for a fact that the harmonic was slightly wobbling and I was going to replace it with a BHJ soon, but I wanted to wait until I had some coin to drop on a real engine from Dr. Fred.

My question is could the crank sensor fail and not throw a code, but then be compensated for (somehow) by the scanner? Could the scaner take over for it?

Could the same be said about the Cam sensor?

What about the timing chain...Could that have jumped and then the scanner adjust for it?

What kind of items should I look for on the diagnostic data to see if any of these are the case. I thought that the 30 degrees of timing was a little extreme, plus I wonder if the car would run at all (with or without the scanner) if the timing chain jumped.

I have access to all the diagnostic data from that computer, so anything anyone has will be helpful.

They are ordering a computer for it tomorrow and starting from there.

ANYONE PLEASE HELP
 
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Have you reloaded the EEC Tuner? You may have some bad data in it. If you did reload it, then take it out while you trouble shoot the problems.

You can rule out the crank sensor. I really don't think it is causing your problems. The car will DIE as soon as it looses the crank signal. Not run badly, just not run.

Next is the cam sensor, it could cause some of the symptoms of your problem, but hooking up the scanner would not make the problem change. Try disconnecting the cam sensor and running the car, if there is no change then it's not the cam sensor.

Next is wiring, have you checked all your grounding staps? A bad or intermittent ground can cause many ghost problems to occur. Check battery voltage.

Next is the computer, try to swap it out with a known good unit.

Aaron
 
EEC Tuner was pulled out

The EEC Tuner was yanked the moment the problems started...I am praying that we dont have to cut into this crap engine...Its not worth it....

Too bad you have to BUY a new computer to test it. Car parts companies suck...They should allow returns for non-mechanical parts like relays and computers.

You can plug in and test a friggin Cisco router and if it doesnt work for your network, return it. That can be thousands of dollars...The auto industry just plain sucks overall for customer service.
 
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crank

true the crank sensor will just kill the engine.
But... don't forget its an electrical piece of crap. Our is a hall effect and works with signal cut out and resisitance in the sensor.
Plus you said your balancer was wobbling??? you should never have driven it at that point.

Ok check and make sure the head of the crank bolt is still in place, if not, one, the hub is moving out and, two, its wobbling, so the chance of crank sensor reading a good signal is getting worse with every engine revolution.

If your hub is fine, then you need to find someone that knows how to check for proper resistance on the crank sensor.

I don't recall right now. (i'm at school)
I just replaced my crank sensor for the second time in two years, last time i broke it, because my hub was coming off (nightmare), this time it went bad.
If i recall right, the good sensor's resistance had something like 500 ohms. and mine was reading like 15 or something.

You got to check on the numbers and know how to check the sensor. I think you read resistance between the two blue wires, you can do this at the plug near the cam sensor. lets see one wire is red, one is green or something and the other two are blue, and blue with stripe, its the two blues you want

Like I said this is from memory from 2 weeks ago so you need to find out for sure, and before you spend any more money

jim
ps. 2 weeks ago when my sensor went, it killed my car twice and twice it restarted right away. go figure
 
Heres the latest...

They slapped a new computer in it and it still has the same problem. I have been wondering about the crank sensor from the start since the harmonic was wobbly. It wasnt REALLY wobbling, but I noticed it and it annoyed me. As far as the way the car ran, that seemed ok until now.

Every once in a while, I would get a complete drop in power like someone "unplugged" the engine and plugged it back in really fast.

I believed this to be the crank sensor, but since it was rare that this happened, I kept putting it off until this spring when I had planned to rip this engine out.

Now that the computer is out of the picture, the mechanic had performed the following tests to rule anything out:

Fuel Pressure @ 40psi (35-40)
Fuel Pulse Width checks out ok
Timing chain is intact and tight
Timing when cranking the engine is at 10degrees BTDC
All coils are functioning perfectly
plugs replaced (needed)
Crank bolt intact
Crank pulley not moving at all
All sensors send back data (no breaks in harness)
Computer stores codes and reacts to scanner (car wont run on scanner unless you get it started and it takes over)
Compression tests were fine
No "noticable" vaccum leak detected (car ran fine under scanner)
All tubes sealed with TBird88 teflon gaskets
Cats are new
Exhaust is new
Gas checks out ok (bypassed gas tank and ran off a pump-machine at 37psi to check for bad gas)

Nothing really left BUT the crank sensor. I am assuming that the timing light when the engine cranks reads from the cam sensor which controls the ignition firing, right?

The mechanic assumed that since the timing light was reading the correct timing that the crank sensor should be fine as well.

I am not 100% sure on that, but I have read where other SC owners have had the engine crank and crank, but not start with a bad crank sensor...

I hope that this is the only thing wrong..

Thanks for any and all input!
 
it sounds to me like the crank sensor.
As far as timing at cranking I don't know.
But the timing light has nothing to do with the cam sensor. the cam sensor simply reads the signal.

I say do it. (crank sensor) These are just all the things that are way too familiar to me with my crank sensor bad.


let us know what happens.

jim
 
Another thought, check all of the ground wires. A bad ground can cause very weird problems. Plugging in the scanner might just "hide" a bad ground temporarily.

You can easter egg the crank sensor, but I'm pretty sure that's not it.

The spark is controlled by the crank sensor. The cam sensor is used to identify the correct plug to fire. The engine will run without the cam sensor because the computer will guess which plug to fire and eventually figure it out. I don't think the engine will run at all if it gets an incorrect signal from the cam sensor, but it will run if it gets no signal at all.

Aaron
 
sigh...

CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...CRANK SENSOR ... CRANK SENSOR... CRANK SENSOR ... CRANK SENSOR...

That will be $100, please.


And yes, the car WILL RUN if the crank sensor is on its way out but not yet completely "broken" (i.e. no signla at all). Amazingly, it will run with the EXACT SAME SYMPTOMS as Mike's car, leading me to the above conclusion.

Let me know when I'm right :)

(Oh, and fix your crank pulley before you blow out the new sensor too).
 
The reason it works while doing the test is most likely because during the test, the timing is fixed at 10 degrees, rather than using the SPOUT signal to vary the timing. Sounds to me like something is either wrong with the DIS module or maybe with the SPOUT wiring.

Somebody correct me if I'm wrong here, but wouldn't it still need a good crank sensor to run properly at fixed 10 deg BTDC?

Here's something you can check easily. Pull the SPOUT plug, and then try to run the engine (without the tester). I bet it works.

If the shop knows what they're doing, they should have hooked this thing up to a scope, and then they could tell you if the crank sensor signal looks good, if the SPOUT signal looks good, etc. This is not hard to do, and they should have the equipment... if not find another shop! Many shops and even parts stores can also test DIS modules. And, they should have done all this before blindly replacing parts.
 
Make sure you ground the computer if you have it just laying there for testing purposes. I have mine loos ewhile doing some other wiring work and have had some weird stuff happen, ground the computer and it goes away.
Rock
 
Got it...

SONOFABITCH...

The first thing I thought of was this because of the symptom simularity when this happened to my 93.

The friggin harmonic was wobbling a HAIR and it bothered me, but I ignored it because it wasnt dramatic. My 93 was doing the friggin hula compared to this thing.

The balancer was still moving, the car would still crank, but when it was starting it was grinding the aluminum to pure liquid.

The mechanic wondered what in the hell this stuff was, took a mirror and found the crack in the balancer.

The new balancer was installed and now it runs fine, but am I now sitting on a ticking friggin time bomb or what...My 93 was wobbling like an inch or two out (yeah, that bad) and I ceased driving it as soon as I saw it, but this one never got that bad...Thank god.

Who knows how much it takes to break a crank, but that is what I am worried about...Time to bring home the 93 for, if nothing more, a spare car.

Thanks for everyone's help on this one...I wish the mechanic would have done a more thourough check on the balancer when I first mentioned it, but him and I were both fooled by the fact that it was turning just fine when the car would run every now and again.

Looks like when the car "only ran on the scanner" it was a MERE COINCIDENCE...Aint that friggin wierd or what...

THANKS AGAIN and wish me luck

Countdown to detonation has begun, I guess...
 
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