P38 - Is the P for Problematic?

Thanks Guys

I think it's a bosch system and 3.5 bar fits well with that.

Next step is to fit a higher pressure gauge I think (just found one in the goody box, and drive down the road with it connect to see what is happening.

I suspect there is a problem, possibly with the pump discharge valve or in the regulator. When the car has been stood overnight, it needs cranking for a good 15 or 20 seconds before it will fire up, as though the fuel manifuld pressure has collapsed. Several of the forums I have looked at describe the same cranking issue in relation to fuel pump problems.

Once again, thanks

Steve

Well - after a great deal of faffing about to find a gauge that I could connect and look at whilst driving the car, the fuel pressure sits happily at 52 psi, regardless of how hard or gently I drive it. So I'm now sure that there's nothing wrong with the fuel pump or fuel pressure control.

The Gas ECU modifies the injector signal and uses the control functions of the petrol ECU to run the engine - as the car runs really well on gas, there can't be very much wrong with the engine management system but the car still doesn't run properly on petrol. It idles really well and for the first 10% of throttle it takes off OK, but if I give it any more than 10% throttle, it coughs and splutters, misfires and pops, makes very little power and takes an eternity to accelerate.

I've checked around all of the sensor connections and can't see anything wrong. My instinct tells me to look carefully at the MAF. Tried disconnecting it and the car seems to know that it's there because the engine note changes when I pull the plug off, but it still doesn't run properly. What I can't get my head around is - if it's the MAF, why does it run so well on gas?

Does anyone have any other ideas of where to look or can anyone tell me how to check the MAF. I considered buying some MAF cleaner but I've seen lots of forums saying this is a bad idea.

Any suggestions would be most gratefully received

Steve

Black fingernails - Irresistible to women and the only reliable indicator of a P38 owner

"Steve Shuttleworth" wrote in message news:B4N9l.259534$ snipped-for-privacy@newsfe03.ams...

Checked the plugs/timing/distributer? Particulary the timing, the vacum and/or centrifugal advance is still working correctly?

Ooo, look I've just found a straw. B-)

Thanks Dave, but it doesn't have a distributor, advance mechanism etc. It's the later Bosch type management system so the ignition is mapped and non adjustable.

Steve

Aw, my straws broken...

But surely the computer still needs to know where in rotation the engine is, presumably there is some form of crank position sensor?

In message , Steve Shuttleworth writes

If it was a straight forward ignition problem you can be sure it would be even worse on gas.

Obviously the one significant difference is the petrol injectors. If you have a system that switches them off when on gas - and most do- and if they are not used for a period of time then you can get problems.

Also is it possible you are still inputting gas when you switch to petrol? (It's usually the other way round because an emulator has failed)

My money's still on some sort of condensation-related issue with the pump supplying moisture to the injectors occasionally. The fact that it runs perfect on gas confirms that it HAS to be a petrol issue on the fuel feed side of things. Badger.

When I started out, I too was convinced it was somewhere between the tank and the injectors. Since then, I've looked carefully at the pressures, parts and petrol itself - all to no avail. It is pumping good quality fuel at 52 psi regardless of engine load. The injectors all appear to be working and it runs really quite well at low power.

Last night,I bought some induction cleaner from Halfords and blasted the MAF. It hasn't fixed it, but it does seem a bit better - so I ordered a new MAF from e-Bay (only 36 quid inc postage). I suspect the MAF because a duff one tends to run the engine lean, especially at high power. On petrol, this would be significant, but LPG tends to be much more tolerant of a poor mixture. The thing is only doing about 10 mpg on average at the moment, so I suspect there is something badly wrong with the mixture and, if it is the MAF, I am expecting it to run better on petrol and worse on gas - We'll see!

Steve

In message , Steve Shuttleworth writes

One other thing is ignition timing, LPG runs better at about 3 degrees more advanced. On the 4.0 litre IIRC the auto box advances the ignition considerably on overrun, so far that even the LPG can cause backfire. Don't know how this signal is generated or what the possibility is of it going wrong. I know it doesn't apply to the 4.6

Managed 2 things today:

Fitted a new MAF - huge improvement on petrol, now runs like a sack of s**t on gas. Borrowed an OBD code reader to find out what is going o in the ECU. Ignition timing is fine, lots of codes, but cleared them all and they haven' come back yet. Mixture trims are max'd out at -25% on both banks. If I drive it on petrol for half an hour, they start to recover, but as soon as it goes on gas they go back off the stops.

Looks like tomorrows job is to Autocalibrate the LPG ECU from basic settings and adjust then fine tune until the short term trim readings are neutral.

Finally fell as though I'm getting somewhere.

Once again, thanks all the way through for the helpful advice.

Steve