P38 3.9 Starting Problems

Still having starting problems with my 1998 GEMS V8 which has been LPG converted.

Have a problem where you turn the key to start and either starts without
any problem, or will just turn the engine and never fire. If you then turn the key to off, wait 15 seconds and re try it will generally start. Sometime you have to wait another 15 seconds but generally it starts on the 2nd go.

Crankshaft & camshaft sensors are fine, if you remove a plug it is sparking when it gets into the problem state, and fuel pressure on the rail is good. Scoping out the ECU, it appears when it gets into its state the ECU isn't instructing the injectors to inject fuel. I have tried a replacement GEMS ECU, replaced the power board in the bECM and tried a new gas ECU. The gas system has effectively been taken out of the loop and the problem still occurs, so it does not appear to be a gas system problem. No problems show on the gas diagnostics and no errors logged on the RR ECUs when looking with testbook.

If you manually inject fuel when it is in the non working state, it will fire and then the ECU will start to tell the injectors to work. I have replaced all the relays to do with the engine in the fusebox and the battery is good.

Anyone got any ideas on what I could look at next as I am now completely out of ideas!

Regards,

Chris.

daft question i guess but have you looked at the air flow sensor connections?
i had the same trouble, cold start (petrol) was fine, hot start (petrol) was bad,very bad but when it fired enough to rev up to 2000 rpm and flicked to lpg it was fine, the problem was a bad connection at air flow sensor, after a wiggle it was fine, sprayed with contact cleaner and been fine for 10 months now! (i keep a tin in the boot just in case)

I had checked the contacts a while ago, but never actually checked the output of the MAF Sensor. I will give it another check and check the output too. Let you know what the outcome is.

Chris.

Checked contacts and output fine.

Regards,

Chris.

its obiously not getting fuel through when in its problem state , quick check is try swapping the fuel pump relay for a know good one ?
rick.

When in the problem state, the fuel pump relay is fine, as the fuel rails are pressurised correctly and the pump is operating without any problem. The problem is that the ECU isn't telling the injectors to open. When I scope the output for the injectors there is no signal shown.

Regards,

Chris.

Have you checked the round plate that the crank sensor is bolted into ? I have seen them work loose and cause intermittent starting/running issues.The engine will start with most of its sensors disconnected except for the crank sensor so dont worry too much about them.
Drop down the half moon plate behind the sump so you can view the tangs that the sensor reads.
The engine must be in a mobilised state or it would not crank.Sorry I cant be more help at the moment but my wiring diagrams are all in my laptop at work,its the fact that you say it is sparking but not injecting that bothers me.

Have checked what you suggest and all seems ok.

Chris.

Have found what the problem was while re-checking the sensor inputs on the ECU.

The throttle position sensor was consistently outputting 4.7V no matter what position.

Have disconnected the multiplug on the sensor and vehicle now starts everytime. New
part ordered and will be fitted when it is received. Can anyone explain why the TPS
reading the value as if it was fully open would stop the injectors from opening.

Of course in the time honoured Range Rover fashion, I am now suffering another problem!

Will start a new thread for it!

Regards,

Chris.

Glad you found it,not seen that exact fault before.Just remember that when you fit the new tps you may need to stick it on Testbook and reset the stored closed throttle position.If the new tps outputs a higher voltage than the old one was set up with the Gems ECU will think you have your foot on the throttle all the time and not allow control of idle speed.