AznDrgn

if your fuel pump is buzzing that means it's straining either from lack of fuel flow to it or there is too much pressure in the line in front of it. This is a very common problem for the 924's and it's normally caused by a dirty fuel tank, clogged fuel filter or just a pump that is on it's way out.

streckfu's

Exactly what my problem was when the reference sensors failed. Only, as long as my car was running, it would stay running. Once I turned it off, it would restart until cool.

Stan944

Thanks for the additional replies.

I'll order the DME relay and the fuel pressure regulator on monday, but it's impractical to replace all of the components mentioned above without knowing what the problem is. Especially the reference sensors are very expensive, and buying used ones doesn't seem like the best solution - who knows when these fail?

Nobody mentioned the fuel pressure damper. Is this a likely suspect here?

Even after I replace these two items, I won't know for sure if I fixed the problem, unless I drive it for a few weeks without problems. So I'd like to get some answers earlier.
I plan to make a few tests when it happens next:

1) spark test - I'll connect an old spark plug to a wire, ground the case, and watch for the spark while cranking the engine.

2) narrowing the range of suspected problems: will mount the DME through a custom made harness, so that I can easily read voltage on the coils of the relay, and on the switchable contacts. Depending on the outcome, I should be able to localize the problem, e.g.: when I don't have 12V on the relay coil while cranking the engine, it means either of the sensors that feed the ECU or the ECU itself is bad. If I have the proper voltage during that test, the problem is with the fuel system.

I can do both tests on the road. I think these should be conclusive tests, I hope I don't miss anything...

Stan944

It all makes sense. Is there any way to narrow it down which of these problems? I wouldn't like to buy the (expensive) fuel pump, unless it's necessary.

I'm thinking of cleaning the fuel tank, and already bought the 1st fuel filter that plugs into the fuel tank (not everybody knows about existance of this filter). Does it make sense to spray the carb cleaner through the opening at the bottom and rub it with a long brash or similar, and rinse with fresh gasoline?

Can I clean the 2nd fuel filter by pouring gas in reverse direction? It's only 1/2 year old, but could be clogged from constant flow of gunk from the tank.

AznDrgn

change out the filters and see if your pump still buzzes. If it still does then remove the fuel sending unit from the rear hatch area and look into the tank and see if it's dirty looking. Take the neccessary steps from there and then once you've gotten all those taken care of if it still buzzes take an amperage reading on the pump itself. IIRC it should only draw maybe 5-8 amps on the 924 and the 944 should be about the same, anything more that and the pump is getting ready to go.

Stan944

Thanks, I'll try to follow this. Can't remove the 1st fuel filter without draining the tank (ironically, it's almost full now...), so might as well check the condition of the tank while doing it.
I'll check the current, this should be a useful test.

Stan944

Here's an update:
- The fuel tank was clean; I replaced both fuel filters, and the rubber hose from the tank. The car still seemed to be sluggish.
- the next day I put a new fuel pressure regulator: the buzzing sound of the fuel pump went away (also consistent with what Clark's garage says). Drove it for 60 km, NO PROBLEMS SO FAR. We'll see...
- I also checked the fuel delivery rate (before switching the FPRs). It was actually more than the specs: 1200 ml instead of 850 ml per 30 seconds -> OK.
- Couldn't check the fuel pressure, because I couldn't find an adapter for the fuel rail (12mm OD, 1.5mm step).
- The mpg gauge still shows strange readings (most of the time at/near max), so I'm not happy yet. I think one of the sensors that feeds the DME is mulfunctioning...

Stan944

...another update:
today it lost power for about one second, and than recovered on its own. Looks like I haven't fixed THE problem.
Any other suggestions?

Chris_924s

coil. wires. grounds. My bet is it's an electrical issue.

Scuba Steve

Did the tach needle jump or dive when it happened? Mine started doing that before it ran worse - what fixed it was resoldering the DME.

Stan944

Chris, you might be right, but do you have a specific method for testing these? Keep in mind this is an intermittent problem, and I need to be able to monitor "it" while driving.
Is there a simple method to test for the spark while driving?

Stan944

my problem is different: the tach still worked when I lost power while driving. This fact, incidentally, rules out problems with the speed reference sensor.

Chris_924s

When my coil went south (2 years ago Feb,, cold Illinois weather- I was driving and it just died..) all the usual suspects had been covered.
Fwiw- my coil tested within spec.

Background- I was running Bosch iridium plugs until then. Had her towed to my wrench and this is what he concluded. New bosch coppers, new coil and he had it up and running in under 30 minutes. HTH

GlenL

Don't see this added:

Make the "triple-jump" jumper. Three 1/4" male spade connectors one one (or two) wire. Check www.clarks-garage.com for details. This will get you going next time it craps out...if it's the DME relay. Also smart to have in the glove box if you don't have a second DME relay. I've got both....after having it fail like you describe!

Chris_924s

FWIW- the "paper trick" will also work in an emergency if it's the DME relay. I carry 2 spare DME relays- 1 is new and the other is modded with wadding paper into the contacts to force the contacts closed-

Be careful- your fuel pump will be on al the time.