help needed with poorly 930

[IPJ1978]

Hi all, i havee just bought my dream car a 86 930, but i did a very foolish thing and ran it out of fuel on the third day of haveing the car(fuel gauge very inacurate!!). the car ran fine before and pulled very strong. since running out of a fuel it has developed a running fault. the fault is a lack of power / hesitation when on boost this gets slowly worse as the engine warms up. i havee changed both the fuel filters, the one in the engine bay wasn't dirty but the one by the rear fuel pump was fairly dirty. i have changed the front fuel pump. i'm a mechanic by trade and have performed a fuel pressure check these are my results;

cold control pressue 2.2bar
warm control pressure 3.55bar
boost enrichment 2.7bar
system pressure 7.15bar

i'm finding hard to find any data on wether these figures are ok or not.
the car starts hot or cold fine. any help will be greatly recieved as i so want the car to perform as it did.....

wur part number 0438 140 054
fuel metering part number 0438 120 085

many thanks Ian

[mark houghton]

The control pressure information for specific years is listed in your shop manual (presuming you have one yet). Off the top of my head, the only thing I see amiss might be the system pressure being a bit high at 7.15 bar. That puts you at about 102 psi, and if I recall you should be less than that....like around 97 psi or 6.8 bar. That could cause you to run a bit lean, but I wouldn't think it would cause your extreme poor running conditions.

How do your plugs look? Are they all burning evenly and the correct color, or perhaps one cylinder is starved (plugged injector). Perhaps by running the tank dry, you sucked up some goo (such as high water content goo sitting in the bottom of the tank from running gas/ethanol blends). Try running a bottle of injector cleaner and see if she clears up.

Finally, though it may not be connected to your empty tank issue, your symptoms also sound like a vacuum or pressure leak. Check to see that your turbo in and out connections, and those on the intercooler are secure. If your plugs are black and sooty, then it could very well just be an air leak (remember, with turbo boosted CIS any air leak prior to the throttle body will cause rich running conditions).

Two fuel filters???? Mine has but one that I'm aware of, sitting in the left front engine bay next to the accumulator. Guess I better be looking for that other one you mentioned.

And oh....congrats on your "new" car! Assistance will be slow to come without some pictures that we can all drool over. It's a rite of passage.

[pdx930]

Spec's for the 930/68 motor are:

System Pressure: 6.9-7.1 bar
Warm Control Pressure: 3.75 + or - 0.2 bar
Boost Pressure: 2.90 + or - 0.2 bar

[JBL930]

Mark, higher system pressure should cause it to run richer, higher control pressure would cause it to be lean. At least that's my understanding? Always learning though so happy to be told that's wrong

[IPJ1978]

hi all, i had a bit more time today and checked delivery rate of the fuel pumps. 800ml in 30 seconds. this should be 1170ml i think. i have ordered a walbro 255lph fuel pump to replace the front pump( the rear pump looks new ) i will test again when i have fitted the new pump. do you think the other pressures i tested need any adjustment? i checked the plugs and they where black and sooty which would point to a rich mixture. i've also ordered a wide band air/fuel ratio gauge so i can then work out whats happening. thanks for the advice i'll keep you posted on the result and will add some more pics when the cars back out the workshop... Ian

[smurfbus]

IMO, walbros are not very well suited for high pressures. Try Bosch 044 high pressure pumps but beware of china knock offs. IIRC the walbro stalls badly at higher pressures.

Anyway, while searching for blwur instructions I came up with a thread that suggested vapor lock as a problem for bad running. So the accumulator might be the cause? Also, when running out of gas some water might have been sucked to the fuel system so try some good fuel system cleaning stuff too to get rid of the possible water. You also should log the AirFuel ratios of the engine to see if its lean when it looses power or if its ignition related giving very rich spikes.

[mark houghton]

Originally Posted by JBL930

Mark, higher system pressure should cause it to run richer, higher control pressure would cause it to be lean. At least that's my understanding? Always learning though so happy to be told that's wrong

Hey Jonathan, far from me to profess to be an expert! My logic was that if system pressures increased, then control pressures would increase proportionally....thus a leaner mixture. But hey, I could be wrong. Maybe system pressure has no impact on the WUR's ability to regulate control pressures, and just causes more fuel to flow (volume) to the injectors - resulting in a richer mixture as you've suggested. I now defer to public opinion on the intricacies of CIS.

Thanks for the feedback, always learning, aren't we?

[lite75]

I would check your WUR as your warm control pressure is a bit low causing a rich mixture after your warmed up. Your plugs seem to indicate that also.

[RarlyL8]

Beautiful car!
If you ran out of fuel you can assume that bottom of the fuel tank crud intered the system. A good filter will remove most of the crud but not the water and water soluable contaminants. You might try running your fuel pumps without the engine on for a lenght of time, say 15+ minutes. This may wash the contaminated fuel from the head and WUR. Do this by jumping the fuel cutoff and putting a trickle charger on your battery so it operates at full power.