jon928se

90GT - 2 hours from home - now sitting in a layby waiting for Xlot to rescue us (hopefully) with a spare LH.

Symptoms - cruising along, juddered once then engine quit. Would only restart by bridging the fule pump relay (replaced the realy but no joy) once started would only run with a light throttle opening - more throttle seemed to give about 4 cylinders firing, no throttle engine dies immediately.

ignition on engine not running - classic LH failure symptoms of injectors clicking.

Question - About 3 weeks ago I had what I thought at the time was fuel pump relay failure. Was towed home and the next morning changed the relay and fired up straightaway. I tested the old (1990 relay) on the bench and it tested out fine. I'm now wondering if the previous failure was actually the LH getting heat soaked then failing temporarily, springing back tolife overnite ?

FWIW the LH is a JDS rebuilt (about 18 months ago and only about 2000 miles since then)

Fingers crossed Xlot will be here in about 45minutes with 2 spare LH brains - so hopefully will get the car back home tonite.

Then comes the diagnostics of what caused the failure - the LH itself or something external caused it to fail ?

Mongo

If the ignition is on and the injectors are clicking without the motor running, that is the classic symptom of an LH Failure. Your incident 3 weeks ago was intermittent and foreshadowing the failure to come. Welcome to the LH Failure Club.

John Speake

LH failure of the type you mention isn't usually intermittant. Remove the lid of the LH and make quite sure the EPROM is securely inserted into its socket.

jon928se

we are now on our way back home - xlot drove for many hours to come to our rescue with an 87LH brain. Thanks Hilton!

Hilton

No worries.. was a good stretch for the '87 - it hasn't had a nice long fast run in a while. Was good to see all gauges staying nice and happy.

I just think you're both quitters for not going on to the camp site and pitching camp in the dark :P

edit: oh - that LH has '88 chips in it if you want to plug the spanner into the car for any reason when you get home, although I suspect you'll be opening a bottle of that bargain red!

jon928se

I think some decent bottles of wine are in order.

Campsite wasn't booked and their receptions all close at 18:00 well that's our excuse and we're sticking to it.

Isn't the 928 world wonderful where a fellow 928er will drive a 4 hour round trip to deliver a spare LH brain to get you going again.

Thank you again Hilton. Next time we venture outside the city limits the LH out of the the other 928 will travel with us.

jon928se

Hi John

I've no real evidence that the failure of the LH was intermittent - the fuel pump relay that was replaced hasn't been tested under load yet - only with Rhonda's Fluke DVM. The two failures may well be completely unrelated.

I'll have a look at the EPROM tommorow morning to see if it's secure in it's socket.

What does seem to work if the LH fails with the clicking injectors is to bridge the fuel pump relay so that it runs whenever the ignition is on ie not reliant on a signal from the LH to turn it on This combined with the clicking injectors and a light foot on the accelerator is just about enough to sustain 10mph in 1st gear - may help you get to somewhere safer to wait for your own Hilton to rescue you.

John Speake

OK John, let me know what you find with the EPROM.

blown 87

Glad you got it going, but what is a layby?

I am guessing it is some kind of parking lot?

VehiGAZ

I also may be dealing with an LH failure, but my mechanic said that the injectors all open and stay open when the key is turned on. Is that a different problem?

He also said that the LH is not grounding the fuel pump relay, so there is no fuel pressure when turned on. He could get pressure by jumpering the relay, but then the intake will fill with fuel.

My failure was very sudden... I put maybe 100 miles on the car over a few days after winter hibernation, and it just DIED on me on the way home from work.

Any ideas?

jon928se

Good question Greg

It seems it's a peculiarly English expression - not used down under either .

Basically a parking area at the side of the road where the road has been locally widened to create a safe parking area. Not to be confused with a "lane" at the side of the road that you can stop in but not drive in, if you breakdown (LH failure) or if the law enforcement agency decides that your fun is over for the day (thankfully not today)

Down under "layby" is the term used where you would go into a store and pay a downpayment on some article you wished to purchase to reserve it but couldn't afford to purchase in full at that point in time.

VehiGAZ

That's called "lay-away" here in the States.

John Speake

The fuel injectors' common return to ground is via the LH ECU pin 18. I've never known one to always ground that pin, but here's always a first time. However you might find a short to chassis (ground) on the lead to that pin, via the CE panel.

Fuel pump not energising is a typical LH fault, but doesn't always indicate total LH failure. If your mechanical shorted the wrong pins on the FP relay base to try to start the car, that can blow up the output stage in the LH. This can be fixed without a total rebuild.

blown 87

Thanks, we also have the issue of the law enforcement guys stopping our fun sometimes.

What they call buying something on payments but not getting until it is paid for is called a "Layaway' here in Dixie.


I have got a plan for when I do the interior in my car which will include a rear seat delete to have a hidden space for a metal, foam lined case for my spare LH, relays and tools, something that will protect them and keep the tools from rattling, cause you just never know when you may need tools and spares.

jon928se

Gaz

Sounds identical.

Fuel pump relay is triggered by a signal from the LH ECU - When LH ECU fails the signal is intermittent or completely missing - bridging the relay means the pump runs regardless of what the LH is doing or thinks it is doing.

When your mech says the injectors all stay open all the time I suspect he means they apparently click like a mad thing in a lunatic asylum and they sound like they are opening all the time. ( my experience suggests they only actually open enough to sustain about 10mph in 1st gear on a flat road)

My failure was (ignoring the fuel pump relay failure - I now have to eliminate that or not as a real failure) a one off instant - judder of about 1 second followed by engine no run failure - only later did I figure to bridge the relay and what revs to keep the engine running feebly.

From your description find a friend with an LH you can swap in - any from 87 to 95 should work OK - or safer put your suspected duff LH in their 928 - to see if it reproduces the same problems. AFAIK a dead LH can't damage an otherwise good 928 hwoever there is the possibility that a random short between power and a sensor input could damage an LH ECU - hence put the damaged ECU in the "good" car. to test it.