flash porsche

Hi All,

I just purchased a 83 928 auto. I was driving it yesterday and the car started to bogg down then clear up as I was driving it. I replaced the fuel filter, it also has a new fuel pump. It seemed to run good. But just before I got ready to take it out on the road. It stalled and would not start. I believe its spark or an emission part because it of the loss of engine power. I hear the fuel pump working and smell fuel. But, I pulled off the coil wire and it has good spark. I removed a spark plug wire and it has weak spark. The cap and rotor are ok with minor corrosion. Any ideas? Thanks.


Joe Flash

Mrmerlin

check the timing marks as well as the distributor marks at TDC

flash porsche

Hi,

Thanks for the reply. The car has been running great for 3 weeks. I was down at my shop working on it tonight. I cleaned the contacts on the rotor and cap. I also pulled a few plugs. It can use a new set though. Previous owner used 4 prong no gap plugs. I got it to start but it stalls right away. So, it seems like there is spark, but I am starting to lean towards the fuel side or an emission sensor. Fuel pump is working and new on tank. Does this car have two fuel pumps? Thanks.


Joe Flash

soontobered84

No, just one pump. Your plugs may be fouled. Easy check!

Landseer

Did you get to go through the procedure of cleaning the grounds systematically?
If not, I'd probably begin there.

Also I'd look for massive air leak downstream of AFM, including where it plugs into the throttle boddy (big O ring).

flash porsche

Hi Guys,

Thanks for your replies. I am going to replace the plugs and check the AFM. I will also check the grounds and relays for corrosion. I want to ask you guys something. Are these cars dependable? There is like 500 archive posts of a no start, hard start, when warm, cold etc. And nobody can seem to truly figure out the problem. Seems these cars play games with you. You think its fixed, but its not. I know troubleshooting is challenging and many cars are headaches. I have fixed and restored many American muscle cars. But this is my first European car. I love this car but I dont want to be pushing it off the road every now and then. Thanks.


Joe Flash

Landseer

Real careful cleaning of the 14 pin connector, top, bottom and inside, too.
Temp II sensor.
Temp/Time sensor.

In my opinion, once you patiently go through, understand and replace parts, it will be reliable.

My DD 84 (same as 83) was badly neglected, abused and needed maintenance. Since I did it the work it has been extremely reliable.

flash porsche

Hi Landseer,

I really like the car and will get it fixed. I worked on it today for a little while. I replaced all the vacuum lines. It will start then die after a few seconds. If I spray throttle body cleaner down the intake, it will run as long as I keep spraying it. Seems like its starving for fuel or its one of those sensors. I have the 928 repair manuals. I need to identify these parts, study and do my troubleshooting homework tonight. Feels like Porsche mechanic school.

Engine starts but stops again

These are the components that could be at fault:

1. AFC relay defective (XVI)
2. Cold start valve leaks
3. Auxillary air regulator wont open
4. Intake air sensor defective
5. Temp sensor II in engine defective
6. Break in wire harness or plugs
7. Control unit defective

I am kinda pissed because I was going to go over to Tampa with Stephen (Iwanna928) and his 79 928 and meet Mark (Tampa 928) on Sat. But I am dead in the water. I have a lot of test equipment. I just need to take my time and get my head straight to troubleshoot it. Thanks for the response.


Joe Flash

Chris Hansen

Joe,

I've had mine 2 years, and also had some stalls/no start issues. Causes of mine were green wire, and old/incorrect relays (thanks, previous owner!).

Once this was sorted out, I've been driving it almost every day. It's been dead solid since I worked out the bugs; in fact, it seems to get stronger with less rattles the more I drive it.

pugtech

Use a cheap noid light (<$5) to confirm your injectors are firing. If not, pull the connector off the L-Jet controller and check power and grounds, and confirm you're receiving pulses from the ignition box. See https://rennlist.com/forums/928-foru...r-pin-out.html

Landseer

There are more potential causes than in the WSM troublshooting chart. Especially with multiple failures which is common when sorting through these cars. If you can get the car in front of Tampa, then he will point stuff out very clearly to you. He's very experienced.

Good advice and link.


Try a three-way jumper in place of the injection relay XVI (30-87-87a). Also make a jumper across the fuel pump relay and see if it runs. XVII (30-87). That might get it running.

The ignition switches alone will fail sometimes, partially even, and cause insufficient voltage.


Don't discount the grounds as no-start contributors. With old relays + insufficient voltage to the coils on them, and with relays feeding relays, anything and everything can be FUBAR.
The little positive wire on the postitive battery terminal feeds the brain. It needs to be clean.
The battery ground wire needs to be clean (plus, the wire itself can look perfect, but be corroded beneath the plastic sheath and hide a problem, causing low voltage throughout the car.
The ground wires above the CE panel on the firewall must be clean.
Same with the ground strap linking the bottom pass side of block with pass frame rail must be clean.
And the ground wires on the pass valve cover (down low, hard to see) are also critical.

When I've had one die completely and not restart, its usually been relays droping-out or failing internally, else fuel. Do you have gas? Sender might have hung up.

flash porsche

Hi All,

Update from the 928 from hell. Stephen came down to help me and I spoke to Mark on the phone. He knows his stuff. This is my findings so far:

1. AFC relay defective (XVI)- GOOD
2. Cold start valve leaks - OHMS CHECK GOOD- POWER GOOD
3. Auxillary air regulator wont open -Hard to get ohms reading-need to try from pinout

4. Intake air sensor defective -OHMS READ GOOD
5. Temp sensor II in engine defective-OHMS READ GOOD
6. Break in wire harness or plugs- Still checking
7. Control unit defective-???

Fuel pump pressure is 39.

Car will only start with Fuel relay removed and will run good and stay running

Car will not start when jumped 30-87 or with fuel pump relay

Power at 30 slot.

PLug in Fuel relay or jumper and car dies.

Car will not restart at all when it warms up.

Checked grounds at front radiator, checked grounds at relay board, need to check more grounds.

Cleaned ignition coil connections.

Why would the car start and run good without the fuel pump relay? Maybe a short somewhere? Or a bad ground that will redirect the current elsewhere?

I hear fuel pump run only after I try and start it. Not when I first turn on the key. Is this correct?

Any ideas will help. I am going to put in another full day on it tomorrow.

Thanks.


Joe Flash

Landseer

I think I would pull the CE panel completely out and inspect the wires in back. Looks like spaghetti. Take your time and move each of them around with a little screwdriver. They sometimes melt into each other and where they cross they short. Gotta really be looking for it.

Not sure what else could be going-on.

Any aftermarket installs? Anyway, I always start by pulling the panel. Its actually pretty easy.

Are the A, B, C, D, etc plugs in the right sequence on the CE panel?

Did we point you to the wrong relays or are you reading the panel notations wrong?

You know , some photos of the CE panel and relays you are working with would really help.

I went through this for months with my DD 84.

Tampa 928s

Well what did you find out?

Landseer

If you put a jumpwire onto relay XVII, across 87 and 30, with the key off, the fuel pump should run.

This is a USA 84, right?