Author Topic: Intermittent starting problem  (Read 7371 times)

BenH

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Intermittent starting problem
« on: 22 August 2011, 10:57:27 AM »
Morning folks,

Twice in the last week I have had a call from the missus, "the car won't start", so I'm canvassing opinion from the collective wisdom here as to how best to identify the cause, and fix it.

Both times it been driven about 3 miles and then left for ~30 minutes before trying to restart. So, it was being started form warm, but not hot.

The first time it happened she simply called me, and I got there in ~20 minutes. And the car started fine for me.

The second time it happened she gave it a lot more cranking before giving up. She then waited ~10 minutes before trying again, when it reluctantly started. But, this time I was left with 6 flashes of the check engine light - lambda sensor.

When it fails to start the engine turns over fine, but it doesn't fire. Having trawled the archives here I've come up with the following list of suspects:

Fuel pump? Fuel pump relay?
DI cassette?
Spark plugs?
CPS?
Lambda sensor?

Fuel pump/relay: It smells quite petrolly, so I think that fuel is getting through. Also, when started from cold I can hear the fuel pump priming. It doesn't always do this when hot, is this correct? (I assume that if the car has only been turned off for a short period there is enough remaining fuel pressure that the pump doesn't prime.)

DI cassette: My understanding is that when they fail the symptoms are misfiring, particularly under load, so unlikely to be this.

Spark plugs: Not sure why these might cause a problem.

CPS: intermittent fault whereby the ECU thinks the engine isn't turning and doesn't call for fuel? Am I right in thinking that t petrolly smell would suggest this isn't the case?

Lambda sensor: "faulty", causing wrong fuel/air mix for starting? Or, is this the symptom rather than the cause, i.e. overfuelling caused it to come on rather than a fault with the sensor itself. After the check engine light gave 6 flashes I disconnected the battery to clear the error, and then gave the car a damn good thrashing to A. make me feel better, B. see if the check engine light would come back on - it didn't.

I have tried to reproduce the problem, with no success. It starts every time for me!
So, where do I start? The missus is refusing to drive the car until it's fixed!
The car in question is a '94 9000 Aero.

phoenix

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Re: Intermittent starting problem
« Reply #1 on: 22 August 2011, 11:41:48 AM »
IIRC the CPS provides the signal to time the sparks only at start up, so I would think that would be the most likely culprit. I don't recall it having any control over the fuel pump.

The flashes for the lambda sensor could be because it has become contaminated with unburnt fuel.

BenH

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Re: Intermittent starting problem
« Reply #2 on: 23 August 2011, 10:18:35 AM »
Thanks for the reply, but surely the CPS needs to measure the position of the crank on every revolution of the engine, not just at start-up?

phoenix

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Re: Intermittent starting problem
« Reply #3 on: 23 August 2011, 12:25:44 PM »
My memory is that once started, Trionic uses info from the burn on each cylinder to determine timing. Something like during starting it sparks all cylinders until it works out which is which.