SoldGuy

Hi All... I've been struggling with a running issue for some time and thought perhaps time to seek help abroad.


The car is an '81 US/CAN 928 with Electronic Fuel Injection. L-Jet I believe. I've had it almost 2 years now as my daily driver and previous records show it had years of driving with only 5k/yr. Many of the hoses appeared original, some very dry etc.


A year ago it would suffer a condition where it sounded/felt like I was missing a cylinder or 2.. it would be very sluggish below 2000.. it occurred more often when I was lower on gas but not limited to that necessarily.. I could park it for 10-15 mins and go into a store and it would go away and drive fine... although if I went to mcdonalds and idled in the drivethrough for 5-10 mins it might return. it was off and on like that all the time. then I might get periods where it ran fine for a few days.


After some repairs it ran better for a period, lately its been running bad full time and I'm scared I'm going to burn it out.


I've replaced most the vacuum lines on the engine I can see. I measured running vacuum off the vacuum T that runs to the fuel regulator or whatever the valve is on the center front of the engine.. and I had 19 in/lbs steady. smoothly fluctuated with throttle actuation. **I have not tested the vacuum system near the brake booster/etc really..** don't know if that would matter. I have replaced the other 3-4 way cluster of vacuum lines on the passenger side as well..


I have replaced spark plugs with Denso twin tips less than a year ago, one of the old plugs had so much carbon buildup from the spark arm thing all the way towards the electrode, I was surprised it could ignite. I pulled 3 plugs on the passenger side last week and they all had a consistant light white frosting to them. I had expected to see one suffering a condition like I found in the old ones.. but no.


I have replaced the Fuel Filter last year with the spark plugs hoping that might be it. no.


I have drawn up the following conclusions on my own:


1. the fuel pump is going... however im having a problem even at idle although it still runs smooth.. it doesn't sound right and still has no power. not sure, never experienced one dying slowly.


2. regulator or damper... I have no way to test this that I know of. I'd need a gauge on my rail I imagine


3.MAF sensor, I'm not sure if I've seen mine.. I've had the lower intake box off and seen this square air gate thing... the body of which felt to just float on some weird round ball in socket style metal gasket or something.. I was scratching my head when I looked at it wondering how it sealed. Did I disturb something here?


4. some other dried up gasket/air leak I created... maybe a bad connection somewhere?


*****Other notes... Sounds like a propane engine sometimes like its just pumping/compressing air... I have my 2nd/last muffler straight piped with turnout but it is popping quite a bit engine breaking.

Thanks, Any help appreciated.
Erik R.

alex70

Many more experienced people here than me but I'll share my experience.

I had an 87 that needed an ECU replacement and later a fuel pump replacement that restored all running issues. Mind you that was after an upper end, front end TB clean up.

Good luck, keep posting.

SoldGuy

Last year it also blew 2 fuel injector hoses. I've now replaced all 4 on one rail.. going to do other 4 soon.. with new o-rings

Wisconsin Joe

L-Jet doesn't have a MAF (hot wire mass air flow sensor). It has the "barn door" Air flow meter (AFM). I don't think that would cause the symptoms you are seeing, but I don't know for sure.

The early 944s had the same setup. There's a good bit of info over in that forum (search "AFM" and "Barn Door").

The Forgotten On

If the spring inside of the AFM is set too tight it can cause a lean running condition. It was very common in 914s with replacement AFMs and caused many of their engines to burn out.

Checks its resistance values with the WSM and see if they are within spec.

Also, change out your plugs to the stock Bosch copper single electrode stock units.

Multi electrode spark plugs, especially ones of the wrong brand like denso have been known to cause running problems in any model of 928. The only exception is the GTS but I digress.

Also, check your fuel dampers and pressure regulator. Sniff the end of them and see if there is a strong odor of fuel or if the vacuum line has fuel in it. If there is, then replace them.

What the real issue sounds like is a fuel pump issue where the pump may be vapor locking due to hot fuel and too much of a pressure drop at its inlet.

Check to see if you have the correct pump. Its OEM numbers are Bosch 0-580-464-017.

It sounds like you have a pump that was designed to be used with the in tank pump found on other years of 928s.

Speedtoys

So, two things can happen.

An engine fire, or you park it and fully refresh the engine bay.

You're being given hints.

James Bailey

And this is a daily driven car ????? if one spark plug was carboned up I doubt it is running lean at least not on THAT cylinder. You could easily have a bad injector connection (the plastic breaks easily) or bad injector or two...But driving around with known weak injector hoses is tempting fate.
As noted put in the correct spark plugs and do a compression test to see if everything is still OK while the plugs are out. You might consider getting a set of new or rebuilt injectors to insure that they are working correctly. And yes the barn door airflow meter sticks into what looks like the bottom of a toilet bowl has a rubber sealing o-ring and is held in place by the bolts in the lower airfilter housing.

SoldGuy

I doubt it's really necessary to replace the plugs. The old.ones were very old.and not an indication of what's going now I doubt. The plugs are single spark/electrode. Just narrow tips for eyter combustion...

mark kibort

that wont tell much an is probably not the issue. the way to check it is to go WOT and see what the voltatge is off the AFM flap door. WOT and 4000rpm is near the max of about 8volts if i remember. another easy way is to get a cheap, narrow band O2 sensor meter . it will show you if you are in the right range mixture wise under WOT.

I dont think its the AFM. rarely are they the issue

the aFM does have a "O" ring on the inside of the lower intake "U". the AFM just slides into that and is a snug fit. if that O ring is gone, that would allow unmetered air into the engine and would /could cause running issues and a very lean condition under WOT

dr bob

Start with basic/stoooopid stuff, like fuel pressure and delivery. The WSM details expected flow and pressure, with the test procedure. The pump depends on good electricity flow, including dedicated wires from the battery to the relay and fuse, then back to the connection in the spare tire well and on to the pump. Clean the ground for the pump. On my car it's also in the spare tire well. Electric problems manifest themselves as pressure/flow problems, so start there before you go stretching barn-door springs trying to mask the problem.

Since many problems like this start out with relay-relay-relay, bypass the fuel pump relay with a jumper for a test drive. 30->87 will run the pump continuously, eliminating the relay from the low flow/pressure problems list.

Mrmerlin

sounds like you have the platinum tipped plugs these will not work as well as the 7900 Bosch silver tips plus they cost less

granprixweiss928

Your excessive carbon build up is a clue my 81 had this due to worn valve guides and seals. Im sure all that oil leaking in messed up the fuel mixture, causing the o2 to read incorrectly

SeanR

If you or someone is going to play around with the "barn door" Clarks garage http://www.clarks-garage.com/ has a decent write up underELECT-22, Air Flow Meter (AFM) Operation and Testing that may be of some use.

Get rid of those plugs and put in your normal copper plugs, the car will thank you for it.

Test your fuel pressure using the proper gauge set up also and that will tell you about the fuel flow.

granprixweiss928

If you chose to get your AFM rebuilt, I used these guys, since they are local to me,

There are others as well.

http://www.bavrest.com/air-flow-meters.html

mark kibort

just measure the voltage when you WOT on the AFM.. make two simple taps into the AFM connector, or at the ecu. buy a AFR sensor meter.(uses stock o2 sensor)
report back. your AFM is fine most likely. that will verify it very simply. how about fuel enrichment switch (should engage at about 75% full throttle)? alll this stuff would be shown by the AFR meter that is one wire to the 02 sensor, and the other two is pos and net on the battery. simple stuff