jej3

Well. The good running lasted just long enough to make me super irritated now. Drove to dinner, fine. Drove home from dinner, fine. Parked it to put air in tires. Started car to pull into garage.... same rough idle/miss followed by green led on IMS relay.

New injectors on order from fiveomotorsport. Hoping I can get them by Wednesday. Going to do other stuff on car in preparation tomorrow night. Too mad at the car to do anything tonight

worf928

I just scanned through the thread looking for "relay" and if I read correctly, you were experiencing the crappy running with the IMS BYPASS installed? Yes?

In my experience a bum IMS relay is uncommon but not unheard of. Just wondering out loud if you had/have two problems: a sticky injector and a bum IMS relay...

jej3

Hi Dave -

Yes, IMS Bypass still illustrated a miss or stumble when increasing the throttle. I don't think it is the IMS relay but do feel the quick loss of fuel pressure might indicate some injectors that aren't doing their job and maybe that is contributing to the hot restart issue.

It's just frustrating but I'm learning LOTS of lessons about what not to do when it comes to injectors (where to buy them, where to send the originals for reconditioning, etc... etc...) Hoping I get new injectors installed and it just works. I'll bide my time doing other preparatory things on the car PLUS I have another 928 to drive if it doesn't work out.

BUT it is frustrating as heck.

jej3

Might sound nuts but I'm also wondering if the static fuel pressure dropping is an issue but don't know enough about fuel flow to say....

Maybe the quick depletion of the fuel pressure after turning off is attributable to leaky injectors or if it really could be the check valve.

Could I or should I test for this scenario?

Fuel Pump and Filter are less than 25K miles/5 years old. Check valve replaced at the same time. Fuel pump in tank replaced with strainer. I have a spare NEW fuel pump with a new check valve that I COULD swap in.

I need a hobby other than reading rennlist

worf928

The static fuel pressure drop is - by and off itself - not the problem you seek. It is, perhaps, an indication that one or more of your injectors is leaky.

At this point replacing the injectors is a very good guess. Since you've ordered them, that's where you should place your bet. You've described symptoms that are consistent with some eff'd-up injectors.

There is a test procedure for determining the cause of static pressure drop. It is not something that you can do with 100% OE fuel lines and you need a 'tool' to do it.

FredR

Irrespective of the root cause of your issue you really need to solve the dropping off of fuel pressure- it will not solve your base problem unless there is commonality [i.e. the injectors are the culprit].

If you lose fuel pressure at the rail the only downside is that it takes longer to fire up as the pump takes about 5 seconds to pressurise the system and possibly a bit longer if the rate of loss is significant [I doubt it though].

If replacing the injectors solves both issues that would of course be very nice- the down side is the price- they are about twice the price they used to be a short while ago but maybe I am losing track of time and it is longer than I think since I last checked!

jej3

I replaced the injectors and that seems to have fixed my static fuel pressure (pressure when off). It did not fix the IMS triggering a green LED nor did it fix the intermittent stumble and vibrations of the engine.

Verified firing of all injectors (stethoscope) and spark on all wires (inductive timing light)

Just for kicks...

While the vehicle was off, I pulled the 02 sensor, did a reset on the fuel injection computer by removing ground for 5 minutes and restarted car. Same behavior exhibited.
While the vehicle was off, I disconnected the MAF, did a reset on the fuel injection computer by removing ground for 5 minutes and restarted car. Less vibration, slightly smoother acceleration

I'm hot and tired. Disconnected the ground and calling it a night. My MAF connector has been taped up for years. I undid the tape to figure out what I taped up years ago. There is one wire with a small exposure (like 1/4 inch at most). I'm going to look at it again in the light of day and probably get some liquid tape to insulate it.

I don't honestly know where to go from here. The LH was rebuilt within the last 8 years and hasn't had a hard life over the last 30K miles. The car is water tight and doesn't spend time outside so not sure how any equipment might be environmentally affected.

Thoughts appreciated!

worf928

You were running without the 02 sensor connected?

Did I read correctly that with the Mass-Air sensor disconnected the engine was smoother? Or was it disconnected and then reconnected for running test?

If the first: When was the Mass-Air Sensor last rebuilt? And by whom? Direct rebuild? Or core swap?

If the second: yeah, examining the connector is a good idea. As is wiggling it while the engine is running to see if running changes. I might do the same for the CPS connector. (Length of brass safety wire with end wrapped around harness makes a useful 'wiggle tool.'

jej3

Sorry to be confusing. My Florida garage in the summer damages my vocabulary.

I disconnected the 02 sensor at the Central Electric Panel (didn't physically pull it) and then ran the vehicle to see if there was any change but there was none. Did the same with the MAF and it smoothed a little.

The MAF was swapped from my 1988 (other 928) which is running fine. I did not swap them back but probably should have. The 1988 (other 928) has this car's MAF which was a swap-out for one of John Speake's rebuilds through Louis Ott within the last 7 years (along with the LH).

I will jiggle the CPS wire and MAF harness to see if there's any effect. Will also put the re-built MAF back into this car just to rule that out, again.

I am under the impression I need to disconnect the battery ground for 5 minutes to let the computers reset when swapping MAF or pulling MAF connector, is that right?

By the way, I'm doing all of this with the IMS bypassed as there may be an issue but there's no visual observance of the cats getting red-hot/glowing.

worf928

If you swap the MAF you do want to clear the LH. However, unlatching it, pulling the connector away, and then relatching is sufficient.

No need if simply disconnecting the MAF.

Ok. I don't suppose there's another 89+ in the vicinity from which you could borrow a known-ok IMS relay?

Did I - or anyone, in this thread, direct you to make sure that the two injection harness grounds at the back of the block are clean, tight, and in good shape?

jej3

Thanks for the ongoing guidance.

I did clean the grounds for the injection harness when I started the rintake refresh 15 months ago. Not sure much has changed.

I dont think the IMS is necessarily at fault and it is probably pointing to something but it is probably pretty subtle.

I'm just plodding through it all, I suppose.

Is it worth swapping the LH withvthe one from my other car?

worf928

Double-check that each bolt for each ground is actually 'wrench tight' and not 'finger tight.'

I would not assume that either. But, if it was easy to locate one for a swap then one more suspect is crossed off the list of suspects.

Swap both between both cars.

One other thing: If you are not already doing so, take copious and clear notes of everything you do, the effect, and the ambient and car conditions. Memory is poorer than ink on paper.

jej3

All good advice. Will do!

worf928

It is all too easy to get so deep into bug hunting that you forget what you did - especially if you 'put it down' for a day or week - and then you end up doing tests over. Also, without clear notes, you may end up second-guessing tests you did e.g. was the engine hot or cold when I did this?

jej3

Did a couple of things today. Engine just isn't smooth and vibrating quite a bit.

1. Re-cleaned driver side Injector Harness ground and added supplemental ground wire between injector harness ground point and ground point in front of Master Cylinder.
2. Started car, No immediate improvement. Manipulated the CPS cable and the MAF hookup cable. No change.
3. Disconnected LH, swapped MAF with other car. reconnected LH and started car. Allowed to idle for several minutes but still absent was smooth throttle response and engine was still vibrating.
4. Same procedure as 3 in the other 928 to run the MAF in it. All good in the other 928. This 928 (1990 S4) is still in question.

I have stopped for now to prepare for our departure to Rendezvous in my 1988 928 and my 16 year old son's 1987 924S.

When I return, I am going to swap LHs between the two cars and some threads have indicated the 02 sensor could be a wear item that has worn out. I can buy a universal Bosch O2 at my FLAPS, 7 years ago I purchased a universal 02 from 928intl so it may be time.

Also, static fuel pressure is better but MAYBE not 100%. 42 PSI at shutdown. Within 8 minutes PSI was 22PSI and within 23 minutes PSI was nearly 0. Not doing anything else to pursue pure static pressure issues (i.e. Checkvalve) but honestly, I'm down to Checkvalve, O2 Sensor and LH, I think.

Looking forward to enjoying driving a 928 with my son's 924S in the rear view. See some of you in HOTLANTA!