aggravation

This morning I was checking the connector for the crank position sensor trying to track down some symptoms and the plug crumbled and fell apart after just barely touching it. So I got both ends loose free from the sheet metal bracket that holds it in place, removed the excess plastic from the socket and was able plug it back together securely and then wrapped it with some of that good self sticking silicon tape that 928 Motorsports sells.
It seemed to be a good repair, the car started right up and once it was awarmed up I took of for a drive. About five minutes later about to pull away from a stoplight the car stalled.
I checked and there was no fuel pressure so IO jumped the fuel pump circuit (removing the relay) and tried to start it...still no joy. The engine tries to fire but dies immediately.

I'm guessing the crank position sensor is bad, or its wiring since it was pretty stiff.
Does the crank position sensor cut off ignition as well as fuel? I kind of expected the car to start once I jumped the fuel pump...

Larry928GTS

The crank position sensor sends it's signal to the EZK computer. The EZK computer then sends an RPM signal to the LH computer and the tachometer in the instrument cluster. The LH computer won't start the fuel pump or fire the injectors if it's not getting that RPM signal from the EZK computer. If your tach isn't showing anything when cranking the engine, there's probably no RPM signal coming out of the EZK computer, and the crank position sensor is probably the reason.

aggravation

Uh oh then..
I just tried to crank the engine and the tach shows the rpm's of the starter turning the engine over and during a brief bit of combustion / firing of the engine...about 1500 rpm's.... but it dies immediately. Basically it dies at the point where you think it's started so you release the ignition key.

It has fuel and shows 55 psi on the fuel pressure gauge when the fuel pump is jumpered. It doesn't build fuel pressure when it isn't jumpered

Larry928GTS

That probably narrows the problem down to one of five possibilities. In no particular order:

1 - bad fuel pump relay
2 - bad LH computer
3 - problem with terminal connection at LH pin #1
4 - problem with wiring or connection somewhere between LH pin #20 and fuel pump relay terminal #85
5 - problem with wiring or connection somewhere between fuel pump relay terminal #86 and the ignition switched +12 volt power supply

Most likely would probably be a bad fuel pump relay or LH computer problem. I'd try swapping in a different relay first. If that doesn't fix it, if possible try your LH computer in another car.

worf928

And in addition to all of the above: the EZK won't fire the spark plugs if there's no signal from the speed sensor.

aggravation

Well all the #53 relays are new. But I have a few spares so I'll try that first.

I have a spare LH but not a spare car to try my LH in...
What do you think the odds are of ruining the spare LH by trying it in my car?

I never really looked at the tach while cranking it before, does 1500 rpm's sound right for a starter motor? It's a heavy duty smaller framed aftermarket one I put in a year ago.

Do the LH and EZK have a minimum speed threshold before they shut down spark and fuel and, on the other side of this, do they wait any time to see proof of speed before shutting it down starting from the time you turn the key?

David L. Lutz

Craig.

Its hard to think your "no starting" problem is not related to the crank sensor, but my LH failed about a year ago and the symptoms I had were idenical to what you are describing here! On mine, if I jumped the fuel pump the engine would fire (a little) and then die.

Its just hard to believe your LH goes bad 5 minutes after you repair your wiring on the sensor.

I remember I called Jim B. and in seconds he said "sounds like a bad LH". Long story short, I relpaced the LH and it started right up.

aggravation

Yea I'm not big on coincidences myself but the tach is showing rpm's while the starter spins it...
I didn't have the battery disconnected when the plug for the position sensor fell apart and one or more of the pins may have touched ground or bridged together while they touched...I don't know if that could hurt the LH or EZK...seems unlikely but then again those pesky electrons like to cause trouble for me.
I sure don't want to throw Tims LH in there, burn it up and find that I need to buy him one and myself one and still not know what is wrong!
I'm off to try the pump relay for now...

Larry928GTS

I've never had it happen, or ever heard of it actually happening to anyone else that I've talked to either. The commonly accepted thinking is that if your car has some kind of wiring problem it could possibly damage a good LH computer if you plug it into the bad car. One of the LH rebuilders could probably give you a better idea of how likely that really is though.

The indicated 1,500 RPM while cranking with the starter is probably not accurate, but shouldn't really matter. The main thing is that you're seeing some reading from the tach. The engine isn't turning as smoothly when being turned by the starter as it is when running, so the tach may display an inaccurate reading due to the more jerky turning of the engine by the starter.

They probably do have some minimum required engine speed, but I have no idea what it is. It's got to be pretty low though based on how slowly I've heard some engines turn with a weak battery and still start.

Based on the idle speed issues that you were having before, I'd kind of suspect a bad LH to be a pretty likely cause. They don't always just quit working all at once, and can cause some weird issues for quite a while before they fail to the point of the car not running.

worf928

Can't say I've ever paid attention to the tach either, but the actual rotation speed due to the starter is more like 150 rpm or less.

Ummm... 1

If the EZK sees an "engine turning" signal from the crank impulse sender it sends a "fire" signal to the ignition amps (which then fire the coils, etc.) and it sends a signal to the LH which sees that signal and turns on the fuel pump relay and starts firing the injectors. IF AT ANY POINT the EZK thinks the engine is not turning (say because you hit a tree) it shuts down spark and tells the LH to shut off fuel.

If you have no spark the speed sensor is dead. If you have good spark during cranking but the fuel pump relay is not turned on the the LH is suspect.

And yes, LHs can fail whenever the hell they want to.

fraggle

You may have intermittant signal, which will confuse the snot out of the computer. Find someone with an o-scope to check pin W23 on the CEL and you can watch the waveform. There's another spot you can check it, I'm sure someone will chime in with the right pin number.

Larry928GTS

The pins touching would not damage the EZK or LH. The sensor basically just generates an A/C voltage in response to the teeth moving past it when the engine is turning. There's no power being supplied to the sensor, so all that pins touching would do would be to stop the signal that the sensor is generating from reaching the EZK, the same as if you just unplugged it.

Hilton

Put your LH in his known-good car - if it develops same symptoms as you have, you know its the LH, and you're not putting his PH at risk

aggravation

I can now testify to that.

I tried the relay and it didn't work so being an impatient bullheaded type, and because Tim's car is nowhere near South Carolina.... and being that the consensus that was building was LH failure....I went right to the spare LH and VOILA! car runs again!

And while I was out on the test run Roger returned my call and a rebuilt LH will be coming my way shortly.
Damn! I better throw away the receipts for the parts and repairs I've put in this thing or else one day I might make the mistake of adding them all up and die of sudden reality check!

David L. Lutz

Don't make that mistake, I think thats one number we both are better off not knowing!

Did Tim's LH solve the high idle problem as well?