89 FUEL PUMP RELAY QUESTION
 

89 will drive fine, then a no start intermittently.
Fuel pump not getting power.
Fuse and relay changed.
Will start with jumper wire in the panel, no relay.
I do not see the tac moving when cranking.
Can a faulty CPS cause no power to the fuel pump relay?-can car run with faulty CPS, and fuel pump jumped?

Do all 89's have factory alarm system?
Is that a different unit from earlier models?
Location under radio?- wanted to bypass it, to eliminate that possibility.

The engine will not run if the CPS signal is not viable.

Sounds as though you need to eliminate the LH unit from the list of possibilities.

Have you checked for spark?

Classic signs of a failing LH computer....especially the running with a jumper wire in place of the relay. And given that it runs with a fuel relay jumper pretty safe to assume it is getting spark.

when did the intake refresh happen?
NOTE post pictures of the engine bay for better advice

when I remove fuel pump relay and jump slot 30 to 87-it runs

intake refresh did not happen yet-
car was running well.
biggest improvement came from relay bypass for exhaust manifold temperature system,

I drove it all day yesterday-stopping and starting-all good-
today I moved it out of my driveway, later I when went to move it back-no start.

the other day I drove it to work no problem, then no start at the end of day.
the next morning it started.

Please post pictures of the engine bay

This is *exactly* what it does. Except that what it does is not tell the LH to turn-on the fuel pump relay.

It also results in the EZK not initiating spark.

No.

You bypassed the system (IMS) meant to prevent unburned fuel in vast quantities being passed out the exhaust.

In my experience, an IMS issue 4 times out of 5 is telling you there's something wrong with the motor and is not a result of the EGTs or IMS relay. (Full disclosure: 5 times is, IIRC, the number of times I've had an IMS issue with a 928 but I work on way more '89+ than I do '87-88.)

When it doesn't start do you have spark and no fuel? Or just no spark? (Since it isn't possible to have fuel along with injector pulses and no spark.)

Last, I agree totally with Stan: it's time for the intake refresh. Post pictures if you have any doubt that this isn't true.

NOTE your picture will tell part of the story of the engine bays condition and this will also be indicative of the rest of the machines condition.
NOTE at this time an intake refresh can and should include having the LH computer rebuilt as well as a fresh MAF and new O2 sensor If these parts are original.

Plus all of the other electrical systems under the intake replaced.

As others have said in diagnosing issues,
once a machine starts not working as it should then jumpers are being installed to keep it working,
this is your machine telling you its time for major repair to happen,
This so that the engine will continue to operate at top levels of performance.

You may have more than one issue. As for the non start the suggestions above should be followed. Greg Brown may differ, but your symptoms lead me to a failing LH computer. If possible find another 87+ 928 and place your LH in it and see if the failure follows the LH.

As for the IMS exhaust manifold temperature system bypass, the first place to look for issues are the spark plug leads. Old leads can contribute to misfires and unburnt fuel entering the exhaust system. Check every lead as it exits the distributor for broken insulation or separation for the distributor connector. Pull every plug and note their condition. A spark plug that is dark or black of smells of fuel suggests it is not firing all the time.

Good luck.

89 S4 intermittent no start-update
I would drive apx 12 miles to work, stop for coffee, then go down the block to office.(7-11)
Car would start fine both times.
Coming out of the office several times, and once after putting the car in the street for a few hours, the car would crank but not start.
I mistakenly thought the fuel pump was not energizing.
This lead me on a path that included relays, fuses, removing an old aftermarket alarm system and bypassing the factory alarm.
After I thought I solved the issue, it happened again.
I then realized that the cranking and no start was because the car was flooded.
I removed the fuel pump fuse, cranked, and it eventually started.
After it died because of the lack of fuel pump, I put the fuse back in and all good.
A more experienced 928 mechanic suggested a leaking injector could be putting fuel in the cylinder after it is shut, causing the flooding at the next start.

I

if this is your main transportation then:

take to a good 928 mechanic and get it fixed...

if this is an occaisional vehicle then swap out the lh and continue trouble shooting...it is fun I know !!!!

seems like I occasionally get the flooding when it sits for a while after morning drive-
then I can drive it, stopping and starting no problems.

I realized I never changed temp II
I put in a new Bosch the other day.
Better cold starts, and I have not had the no start since.
fingers crossed-duh me

Correct, this is not my car
It's an 89 (this why posted in the 89 relay post). This is not my first rodeo. I flew out here to Vegas to help owner to just be a nice guy and help after he did all listed below. I posted in the 89 relay post to see if anyone had an "aha" answer that a very specific thing caused their failure but I'm happy to answer this.

It's a rebuilt Lh, owner got it
It's a rebuilt Ezk, owner got it
It's a rebuilt MAF (John speake I believe)
Has a VCB supercharger (problem was prior to this as you'll see below)
New hall, cps sensors from Roger
New Greg brown high output alternator (which as a side note is fabulous)
It is a new to this car CE panel which owner sourced (replacement didn't solve issue)
All the relays are new
Yes I have wsm in both printed and digital form with me and have been referencing them.

Stan (Mr Merlin) and I have been working back and forth on phone (he was going to come out and help but got busy). I don't have my tools as I didn't want to ship everything. So I am limited to what owner has here. I did have a Power Probe shipped to test ports and test downline wiring.
We are checking FP socket today after my wsm research last night points to what you referred to . We have narrowed it down to that. Stan, Victor Edgar and I have come to the point that it is pointing to the LH. I am taking them home with me (new and old) and testing in my car. We believe this due to car running perfectly with FP jumpered. That eliminates the CPS. What we do need to find is why the LH went (if found to be bad). In tank fuel pump seized (there goes a $1000 part since it sat in car for 8 mos before it got here) so Roger sent me a strainer kit. Wondering if that caused an LH failure? Maybe Alan will know. He's the electron wrangler.
Owner told me (he is second owner) that in his discussion with first owner the car had a "gremlin" since new that caused car to die. Dealer couldn't resolve it. I believe this is why current owner threw all the parts at it.
He does also have a complete car harness and was about to pull interior and put in new body and engine harness. I told him to trace every wire with power probe and verify continuity (power probe can also tell you how far down a wire there is a break as well).
Owner has time and resources to do this so it can't hurt and can do this while I have the LH with me testing it.

How's that?

As an update Louie Ott did both computers on the 89

I know a similar issue was diagnosed and fixed following Greg Brown's advice.
Here's what I found: Hope this helps.

Vanster: Yesterday my trusty 86.5 would not start....It always starts! I checked everything then went to the fuel pump relay. By passed it with a jumper and it starts. I have a box of relays tried them all..nada
We do my local Porsche parts house and got a "used" relay...still won't start. Jump it and it fires right up. The fuel pump has about 30k on it.
Any suggestions?

Greg Brown:Lost power or ground to fuel.pump relay. You can put common test light across "85" and "86) of the fuel pump relay socket (while cranking) to confirm this (relay out)..Then test each "85" and "86" individually to ground (while cranking) to see if you have power on either.

This will tell me a bunch.

While people are saying that losing signal from LH to fuel pump relay is a common problem, I've never seen this.....and I've seen a bunch of LH failures. I can send you up a rebuilt JDS computer to test, if necessary. (I'm thinking I would have put a rebuilt in, BTW.)

I'll call in AM.

Vanster: With a little help from GB on the phone we managed to resolve the issue and it runs perfectly again. We ran a wire from #85 on the FP relay to the #21 fuse block ( the brown and white ) wire on the lower right of the panel ( yellow block). All is good. My first thought that it was the LH, but since it wasn't that old ( 35pin) I needed to check all options before sending it out for repair. It could be a loose wire or something behind the big board ( which gives me a headache just looking at the back of it).

FWIW, it's my 89. Jeff is a true friend coming out to Vegas to help me out with this problem.

Dr. Bob wrote this:

The LH doesn't source voltage to close the relay. The relay coil gets power from the 15 bus (hot with key in RUN or START). The LH controller **GROUNDS the other side of the relay coil, causing the relay to close.
The "fix" was to the hot side wiring so power gets to the relay coil. The ground (LH) side of the relay coil wiring was fine.
** the LH actually pulls its side of the relay coil almost but not quite to ground. It ends up floating somewhere around 0.6 Volts above ground, thanks to the silicon transistor used for the switching inside. Probably not important unless you are in there with the DMM trying to figure out why that side of the relay isn't "properly" grounded.

Excellent!

Given "the car had a "gremlin" since new that caused car to die. Dealer couldn't resolve it" my crystal ball says "wiring harness." Dealer techs, working mostly on new cars, hating 928s, knowing mostly about 911s, rarely seem to have developed the wherewithal to dive into a 928 wiring problem even if its suspected.

However, the LH rebuilt or not is still a potential culprit(*) if your relay socket diagnostics indicate that the socket isn't being 'turned on.' If so, then 'skin' the LH multi-pin plug so that you can put a multi-meter probe on the back of connector for the wire that runs to the FP socket. Check for continuity. If the socket doesn't 'turn on' during cranking and you have continuity to the appropriate socket terminal then the LH is dead.

(*) Not knowing who rebuilt the LH you don't know if it's really good. I only trust JDS and Elektronic Repair for LH. I don't trust any other rebuilder and don't trust "Porsche"-rebuilt LHs. Look on the LH's case for a rebuilder's sticker.

Nevermind the LH. Louie is JDS's domestic rep. So, the LH was good when it was installed. You've got lots of good info now on testing the FP relay socket. Hope that's it and the fix is straightforward.

Last, it's great to know that Joe's getting some additional well-trained hands on his 928.

Right! It's important to remember that most everything is ground-switched not power-switched. Test that you have power to the pin (under the correct conditions for the specific power bus) and then chase ground-switching on the other side.

Me? Not me. That was at the direction of Greg Brown.

Jeff, spoke with Louis Ott, and after discussing every thing that we've done to diagnose the problem, Louis agreed it's probably in the LH computer. I'm pulling it out tomorrow morning, and sending it back to Louis. Electrical ain't my strong suit, and I just let the car sit for most of the year. It would still be sitting if Jeff hadn't come out to help me out!

Runs like a scalded cat with a jumper wire. It's like that old saying:" If it's got tits or tires it'll give ya problems."

Its great that Jeff came out to assist you,
we will figure this out, one way or another,
sorry I have not been able to launch.
The thing thats bothering me is the remark that the car has had a cutting out issue from day one,
This sounds like a crossed wire shorting something. maybe a pinched harness from when she was built,
and so far it has not been found.
I wonder if this same issue could be damaging the LH if infact it is damaged.
Thats why it would be good to swap this LH into a good running machine to test it
Ima keep noodling this

Joe is prepared to pull the entire harness out of the car and put in a new one. He has another harness and is prepared to test continuity of every wire in that harness prior to install. Extreme but would eliminate the problems as long as it didn't cause others.

Would be interesting to get the results of the power and ground testing at the FP relay socket. I suspect that relay ground through the LH is based on the connection at the back of the intake, same one that injectors depend on. Make short jumpers so you can dangle the relay a bit away from the CE panel and read voltages in service.

If the FP doesn't run with FP relay jumpered, look hard at the fuel pump power circuit that starts at one of the smaller red wires at the battery positive. More than a few wacko FP symptoms start with a less-than-stellar connection at the battery terminals.

We are able to run it jumped.