Hi all

I've been searching the forum for solutions to this, and I've picked some pretty good tips about tapping the relays, jumping the fuel pump relay etc, but I'm still having some problems ... here's the story:

- About 2 weeks ago, I stopped the car an couldn't start it again. Cranked it but no fire.
- I searched the forum and subsequently gave the relays a good tap with a screwdriver. Hey presto it started first time, and second time.
- Tapping didn't work the next day, so I ordered some replacement relays for Fuel Pump and LH Jetronic, and in the meantime jumpered 15 and 87 on the fuel pump relay. Started like a dream.
- Yesterday I installed the new relays, but no start. Jumping the terminals on the fuel pump relay also didn't work (although the pump runs).

So ... what should I try next ???? Please tell me I don't need a new Jetronic ECU !!!

Thanks in advance

Martyn

89/90 928GT Metallic Slate Grey

 

Marty, I feel for you. The last thing that you want to do is replace the brain! It costs too much. So I think that what you are doing is right. What about the check valve at the pump? They are cheaper than the brain about $18.00. And then you could try the temp two sensor. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />

Chucker
1982 928 White

 

Back to basics:
Fuel, fire, air, compression, timing - the necessities of life for an engine.

The fuel pump relay is one of the usual suspects - but if the engine won't run with the fuel pump running, you can mark that one off the list of suspects.

Since we are at the central power panel, first push and wriggle each of the plugs at the bottom to make certain that all are tight.

Use a mechanic's stethoscope (a very useful tool, on sale at Harbor Freight for $3 in the USA) or a long wooden dowel to listen to the injectors.

First, turn the ignition on, but don't try to crank the engine. Listen to the injectors - if they are clicking, the ECU is probably bad.

Then, have someone crank the engine as you listen to the injectors. They should be clicking as the engine turns over. If not, the first suspect is the LH relay.

If the fuel pump runs, and the injectors click only while the engine is turning, suspicion moves to the ignition. THE IGNITION ON A 928 CAN HURT YOU!! The safest way (for both you and the car) is to use an inductive-pickup timing light to check for voltage on the plug wires.

The next-safest way is to get a conventional spark plug, open the gap to about 0.050". and fasten it firmly (metal-to-metal) to a metal part of the engine or the chassis, then pull a plug wire and attach it to the plug. Crank the engine and watch for a regular, hot blue spark snapping across the gap.

NEVER try to crank a 928 engine with a disconnected plug wire - the system is capable of VERY high voltage, and if a plug wire is off, that voltage is going somewhere, even if it has to go thru the plug wire insulation, or thru the rotor to ground, etc. If you are holding the plug wire, it will go thru you - and this can be more than just a shock. This is a POWERFUL system!

I suspect that one of these will be your problem - if not, let us know the details of what you do and what happens.

 

Thanks for all your suggestions ...

I checked for injectors ticking, and they didn't unless I cranked the engine, so hopefully that rules out the ECU ....??
I also changed the LH relay at the same time as the fuel pump relay.
I checked for a spark using a sparkplug tester, but it was difficult to see anything due to the depth of those holes !! I'm pretty sure there was no spark though.
Fortunately I have a Porsche specialist about 10 miles away, so I'm going to flatbed it over there.

Thanks again

Marty

 

Before you do that, why not swap the ignition relay with one of the other "53" relays? Might be cheaper and easier.

 

... each new suggestion I try with boundless optimism !!

But, alas no.

I also cleaned the contacts on the HT lead between the distributor and the coil on the suggestion of the Porsche garage. I have until next Thursday, but then it's booked in to the specialist. Fortunately I don't need to use it every day !!