Timetrader22

Hi, I'm really out of ideas and need some help. I have a 1987 928s4 automatic. I have owned the car for approx 5 years and I drive it as often as possible, approx 10-15K miles per year. About two months ago I backed the car out of the garage and washed it and then put it back in the garage. A couple days later it was beautiful out so I started the car and attempted to back the car out of the garage to go for a drive. I put the car in reverse and as soon as I touched the gas pedal it stalled. That had never happened before. I started the car again, touched the gas pedal and it stalled. Repeat repeat repeat...

I pushed the car back into the garage and started trouble shooting.

Here's the best overview of the problem that I can offer: The car usually starts easily, unless sitting for a couple weeks and then I need to rotate the key and cycle the fuel pump to get it to start. Once running it idles solid at 700-750. If you attempt to press the gas pedal the engine will stumble and stall immediately. It will start right back up and idle strong. If I mess around with the quadrant to adjust the throttle and move it ever so slightly I can get it to idle up to approximately 2200 to 2300 rpm at which it stumbles and misfires badly, sometimes even backfiring. Again, if I continue to carefully adjust the throttle and I can get the engine over the 2300 rpm line it revs freely to redline. Also, if you put the car in gear (reverse or forward) the engine at idle is strong enough to move the car but putting any load on the engine causes it to stall.

So, at this point the car can't be driven and I'm really running out of ideas.

So far I have changed and or serviced the following:
- New Fuel Pressure Dampeners & Regulator
- New Throttle Position Sensor
- Flappy Valve serviced and seems to work correctly
- idle stabilizer seems to work correctly
- all new ignition wires, caps, rotors and coils
- new knock sensors, crank sensor
- new fuel pump and filter 1 year ago
- new O2 sensor
- all vacuum connections checked and seem to work correctly
- new soft fuel lines
- Fuel injectors cleaned and tested good
- The MAF was rebuilt/calibrated in 2012 before I bought the car by Elektronic
- Fuel pump relay
There are a number of other service/maintenance things that I have done to the car but they shouldn't have anything to do with the engine running.

Has anyone ever experienced something similar?

Anyone have any ideas on something else I should be trying?
(there are no 928 shops that I've ever found near where I live so I'm really trying to resolve this myself)

Thank you in advance for any ideas or help you may offer.

Tim

worf928

A correctly functioning ’87+ will not operate the fuel pump unless the engine is turning. If what you write above is accurate then your LH ECU has failed.

In any case, given what you have already replaced and the symptoms you describe, LH failure would be a possible culprit. It would be a good idea to send your LH to Rich at Electronik and have him test it.

Timetrader22

Hi Dave, thank you for your quick reply. I'll get the LH ECU out today and send it to Rich.

To clarify, to get the car to start after a couple weeks of sitting I do actually have to turn the key and let it crank and repeat that process for 3 or 4 cycles to get it to start. (not really just cycling the key as I had written)

Koenig928

Check and make sure all the engine ground points are tight and clean. Also, specifically check the 2 points at the back/top of the engine where the LH harness grounds to the block (underneath the rear fuel pressure dampener/regulator). With all the work done you described, the intake has been off and the LH harness has been moved around, so it's possible something is a bit loose or a connector isn't pushed on tight.

This happened to me on my '87 after I had the intake off the first time, the engine would stumble above 2/3k rpms because I didn't tighten one of the LH harness grounding bolts enough on reassembly.

Bill

Timetrader22

Hi Bill,

I did have the intake off and just re-installed it last week. I will go back this afternoon and look for the LH harness connection and grounds and make sure they are all connected properly.

Thank you.

Jason89s4

Does this 3-4 crank-before-it-will-start issue happen even after you changed the FPR and damper? When was the last time you changed the fuel filter and fuel pump? (And filled the car with good gas.) I would test the fuel pressure just to eliminate that as an issue.
Also, be sure the connection to your MAF is clean and secure. Look at the pins to make sure they are all still there. If you have a loose or bad MAF connection, your car will start and run, but as soon as you give it any throttle it will die--sort of what you described.
It may be a failing LH-ECU, but if the car will start and run I would keep looking elsewhere first. The easiest test of the LH would be to take your LH unit out, plug it into another 928 and see if that car has the same symptoms. So, if you have anyone in the area with another LH 928, pull yours, go to them, buy them lunch and try that.
-Jason

Timetrader22

Hi Jason, if I have been using the car it starts right away but if I leave the car for a week or two it does take several cranks to get it going even after I changed the dampeners and regulator.

That is one of the things that really confuses me. Where is the fuel going? Why is it not staying pressurized?

The fuel pump and filter were changed approximately 1 year ago... 8,000 miles ago. I have purchased a new fuel filter and I have another pump so my plan is to swap both of those tomorrow.

As for swapping my LH ECU, I don't know a single person with a 928 near me. They seem pretty scarce in Ontario and Canada in general.

Thank you for your thoughts... I will look at the MAF again tomorrow too.

Tim

worf928

Ok. That's a materially different symptom and I have different advice...


Two things:

1) The fuel system isn't going to stay pressurized for weeks. The spec is to hold system pressure for 20 minuites. You might reasonably expect a very-well functioning fuel system to hold pressure overnight, maybe a day or two.

2) How do you know that your initial no-starts are due to lack of fuel?

Awright... let's back up the bus here.

It wasn't clear from your first note that you'd had the intake off *last week*!

Start at the beginning. In particular:

- did this hard-start and running issue develop before or after the intake R*R?
- if after, why did you R&R the intake?
- why did you replace the dampeners and regulator ($1500 in parts at current prices.)
- did you replace the crank position sensor?

Having someone test your LH is a good idea because *all* LH 2.3 ECUs *will* fail and '87 LH ECUs that haven't already failed are pretty rare in my experience.

When you pull the brain case and remove the LH, look at the back of it where the shell is clamped. If it has already been rebuilt you may find a sticker along the lines of "rebuilt by XX Co, warranty void if seal broken"

Tell us if you don't find a sticker and tell us what's on the sticker if you find one.

Timetrader22

Hi Dave C,

Here's where I'm at today.
I checked the LF ECU wiring grounds below the back of the intake and they are good.
I just swapped fuel filters and the fuel pump. No change.
I removed the MAF and cleaned it with MAF cleaner. No change.





Actually the engine runs exactly the same whether the MAF is connected or not.





Today paying really close attention to starting, idle, running and throttle response here's my findings.

The car starts within a couple revolutions on the first try. When it starts, it hunts up and down several times but within a second or two and then levels out to the 700 rpm area. Still if I even touch the throttle the engine stumbles and stalls. That said, if I let the engine warm up a bit then I can kind of wiggle the throttle back and forth and eventually get it to idle up to around 2200-2300 rpm where it starts to stumble and miss. Also once I get it to the area I can actually rev it through the misfire and rev it through the upper rpm range and right to redline. As I release the throttle it stumbles on the way down around the 2300 rpm area then goes back to idle.

The engine problem literally happened overnight. One day I drove the car, the next day I couldn't touch the throttle without it failing. That is why I did the intake refresh to ultimately replace what I thought may have been a bad TPS. Thinking back, I immediately thought it was a bad TPS because in the days before the problem that I have now I would be driving the car and sometimes have to pump the throttle pedal to get proper acceleration.




As for your last couple of questions,,, I replaced the dampeners and regulator and all soft fuel lines as those were the last thing for me to refresh in the engine bay. Literally everything under the hood has been done. All ignition components, belts, waterpump, timing belt, radiator, radiator hoses, thermostat, temp II sensor, temp sensor, motor mounts, oil filler gasket, vacuum lines, flappy valve, valve cover gaskets, ... there may be more that I'm forgetting....

Yes I did also replace knock sensors and crank position sensor.

I will pull the LH and send it somewhere and I think I'll send the MAF too. I'm so frustrated but determined.

Any other suggestions are greatly appreciated.

Tim

Kiln_Red

I would start here. I would send the MAF to John Speake of JDSPorsche (in England) to be rebuilt.

Jason89s4

If it runs the same with or without the MAF plugged in, then logically you have an issue with the MAF or associated wiring. As I think Dave (Worf928) would say, if it is the original MAF then a refreshed one will be a sound investment regardless. That being said, I’m not a big fan of throwing parts at a problem until something sticks. I would eliminate any possibility of a wiring/connection issue first.
I’d send you a MAF to try out, but I’ve found sending things back-and-forth to Canada isn’t fun.
Pinging, anyone out there in Ontario that can help Tim out with a swap test?
-Jason

worf928

That is where the data points. But,

so,

I would send it back to Rich (if indeed his sticker is on the unit) and give him chance to take a look at his work.

I find that you never really know someone until either
- you take apart their work
- give them a chance to look at failures/mistakes/problems that point back to them
- review the source code for their software (albeit a bit off-topic that one.)

I agree. I prefer to follow data from tests. On the other hand, I'm also a big fan of rebuilding MAFs and 2.3 LHs before they fail because we know that they have limited lifetimes.

Now that there's more complete context, the above, coupled with the completed intake R&R, does, in my experience, point to MAF and/or LH.

There are at least two different 'hardware' versions of the Mass-Air Sensor (I prefer to use MAS rather than MAF (sensor)) and the earliest version has a unique-to-it failure mode not associated with deterioration of the hot wire. And that failure mode is as you describe.

Timetrader22

Hi Jason,
Thank you for your efforts in trying to find someone with a MAF that could help me do a quick test

The MAF or MAS in my car was rebuilt in Oct 2012 by Electronik. I bought the car shortly after it was rebuilt but I have put 60,000 miles or 100,000 kms on it since then.
When I took the MAF/MAS out today I did notice that the rubber surrounding the electrical connector is a quite brittle. I'm going to investigate this more to make sure I don't have a failed connection.
Would you expect this rebuilt MAF/MAS could be faulty already in 7 years?

-Tim

Timetrader22

Hi Dave,

I feel that it is probably a very logical step to send both of these components out to get tested at the very least and refurbished if required.
I'm not afraid of hard work in keeping my car running well (research and actual repair) but electronics are way beyond my skill set.

I will send the MAS back to electronik, his sticker and repair date are on the unit.
Where should I be sending the LH?

Thank you,
Tim

Jason89s4

Personally, I would exhaust this investigation before I sent parts to England.
-Jason