Garth S

Luc,
The O2 sensor does not influence starting the engine: if you needed to experiment with it, disconnecting the 3-pin plug would have the LH default to a 'safe' air:fuel ratio ( as the engine warms up) when its signal is called for ... IIRC.BTW, the O2 sensor output is easily checked on your meter shortly after the engine fires up (0.2 - 0.8v on the black wire to ground.)
When the spark plugs were changed, you had mentioned one to be black with soot - was it just the 1, or 4 ..., or all 8?
As you had checked the vacuum side of all three dampers & FPR, then the fuel pressure leakdown is either the pump check valve ( which may make starting more difficult, but shouldn't prevent starting) or one or more fouled injectors; Still, this should not prevent starting - it may not run well once started, but should continue to run

oups59

Garth,

I found a small fuel leak and now the fuel pressure is at 3.8 bar (54 PSI) and stay there. I tried to start the car and no start. (When I reinstalled my LH after getting it back from JDS, it fired right up !!! then it will not start)

Check a spark plug and it is wet. So there is fuel going to the cylinder.

By the way, all old 8 plugs were black with soot.

Garth S

Hummmmm ..... do you have access to a timing light? Start with the coil wires - and if 'fire' is present, then start with the plug wires. If no timing light is available, you can get a card of 4 ignition 'test lights' for <$6 from places like Princess Auto - they plug into the ignition lead and flash orange when a live lead is firing. The easiest spot to insert is between the cap and the plug lead.

Brett Matthews

Did YOU test the MAF, and what readings did you get?

oups59

Can relay XVI (EZK Ignition System) be the problem? I did not check that one.

Garth,
I will get a Ignition Spark Tester ASAP.

Brett,
I tried with or without MAF, same results

Thanks

Brett Matthews

LUC,
Yes, a failed EZK connection will cause a no run, but I don't know the symptoms...
Ahhhh, "with or without" the MAF, I don't understand? Did you follow the diagnostics in the WSM, with an ohmmeter?

And, while the MAF is off the rubber elbow, as your car is as old as Rosy, maybe, run your finger around the inside of the elbow, and try to feel for a "line". Rosy's elbow had a 1.5-2 inch long through crack! Started at one of the breather hose ports. I doubt this will be your problem though.... Just another WYIT check....

And another little caution here, just for YEUCKS!!!! sake; I found the inside of the elbow to be FILTHY, sticky, gunk-y! To make any feeling around best, I'd take a rag/cloth with some cleaner soaked in, and de-filth the elbow, before feeling around it. Better chance of actually finding an existing problem?
This filth extends to and past the throttle butterfly, clean as far in as you can reach. Rosy's butterfly actually had a ridge starting on the edge!

Bill Ball

Leave the plugs out to dry out the cyls for a while. I dealt with a flooded 928 once and it was very hard to get it started.

oups59

Today, I decided to put back on my RMB instead of the original muffler since this was the only change that I made between last November (winter storage) and January when the problem occurred.

What a surprise, the car started up and I was able to let it run more than a minute with a rough idle. The fuel mixture is still very rich (black deposit on the RMB) but very little smoke out from the exhaust.

So it seems that a less restricted exhaust flow helps.

What can be the cause of a rich fuel mixture?

1. O2 sensor (already bought a new one)
2. Faulty MAF (need to check that)

Anything else?

I also found a small vacuum leak from the AT modulator. Can that have a impact on idle and/or mixture?

Rich9928p

The major causes of a rich fuel mixture are:

a. leaking fuel pressure regulator (pull the vacuum line, look for fuel running out)

b. Faulty MAF - easy test just unplug it, see if the engine runs better (in limp mode, only two injection pulse widths are produced). It may take opening the throttle a little to get it started (starts easier if you do this when the engine is warm)

c. Failed LH fuel injection controller. One (of the many) failure modes is a very rich fuel mixture. Eventually, the mixture becomes so rich the engine won't run. Other LH failure modes include

- clicking fuel injectors when the ignition switch is turned on (and engine isn't running).

- bad idle speed regulation

- intermittent stalling (terrible to diagnose)

- no-start at all

Garth S

There is not much back pressure generated bt a S4 muffler .... unless there were some small furry critters using it for a winter home: yes - it happens .... BTDT

Brett Matthews

Any vacuum leak is not good. I THINK the modulator is given constant immediate vacuum? Not the vacuum from the vacuum reservoir?

Yeah, I just looked it up. That immediate vacuum also controls your regulator and fuel dampeners. You MIGHT just have found your trouble point. The regulator and dampeners are NOT getting full vacuum. I don't know what these results will give you....
The immediate vacuum comes from the top of the throttle body, and goes to a "vacuum spider", which sits on my '87, at the rear of the engine, centered but slightly to the driver's side, at the back of the block. It's also under items, somewhat hard to get to.... When you turn the engine off, the immediate vacuum disappears, of course.
There is another port near the same location, that individual line goes to a vacuum switch, "venting" the activated charcoal canister. On my '87, on the underside of the throttle body, there were two more vacuum ports, one went to a capped off line, the other went to some vacuum operated "thing", bolted to the passenger side exhaust manifold...Might have something to do with emissions control?

oups59

I checked all plug wires and coil wires, OK for those.

I am now removing the intake manifold. I will send the injectors to a balancing and blueprinting fuel injector service. I will check all injector's connectors with a NOID probe. WYIT I will replace both knock sensors,vacuum lines, hoses,oil filler gasket.

Hope that will solve my problem

Imo000

This is how things get really expensive in a hurry! You are replacing/rebuilding parts that not necessarily need to be changed. Either have the car looked at by a pro or start testing each component before deciding to rebuild or replace. Over the years I’ve seen several 928 owners do the same thing and at the end a simple problem escalated into a +$3000 repair. All because they started replacing parts at a whim.

I’m not sure how much the cleaning of the injectors will cost but you can get a brand new set or 8 for under $200. The RMB and the rear muffler have nothing to do with the problems you described. It’s possible when you lifter the car, something broke, disconnected, shorted out, etc.

Mrmerlin

Hi I got a new set of the 4spray injectors from a ford crate engine they are 19 pounders for 200.00 off of Ebay see Five O Racing, they are almost a drop in with the exception that i had to put all of my O rings onto the new injectors the I would also recommend that you check the timing marks and get a set of Bosch silver tips the cheap ones and install new plugs it sounds like you may have a fouled set in there now, Stan
Also if your looking for new injectors try this ad on Ebay item number 8040766558 they are for a ford mustang but will also fit the porsche s4 motor they are 19 pound injectors with the series 2 design that has the 4 spry design offers better fuel distribution, the onlt thing that must be done is to transfer your O rings to the new injectors as the ford O rings are too small

H2

Does anyone know how this hard start problem was resolved?

H2