1984 Porsche 928

[eddyj1]

My 928 sat for around 12 years and I just recently started working on it again. I had to have the ECU rebuilt and I replaced the fuel pump. The car started and I was able to take it out. Now the car just cranks and I dont get any spark at the plugs all the way back to the coils. both coils have power going to them, but nothing coming out. I also dont seem to be getting any impulse at the injectors....I have heard other people saying that its the speed sensor...I notice when I crank the car the tach jumps all over the place, is this a sign confirming this? Also where is this green wire people speak of......I have had that spark problem just recently but had injector signal now I have neither...please help.

[MPDano]

Grounds first, then Green Wire.

[eddyj1]

after I checks the grounds, where is this flywheel speed sensor at exactly? because like I was saying is the tach jumps all over when you are cranking

[Landseer]

You've got to tell us if its a USA car or not.

If you don't know, then post some pictures of the engine and I'll tell you.

The 928 was offered with two unique engine management systems during 1984. One used a pickup in the distributer and a green wire leading to a spark box on the inner side of the pass. fender. The other used a crank position sensor in the back of the block, reading essentially flywheel position, and that signal was fed to a new type of spark box that was co-located with the injection box in the passenger cockpit area.

What is your general location? Maybe one of us terminal hobbyists is close-by.

[eddyj1]

Ok, mine is a 1984 Euro 928s with the 4.7L motor with two distributors and two coils....both coils have power to them, but now voltage out......I have replaced most relays in the panel and cleaned all contacts to the fuses and on the panel. and my fuel pump is not activating unless I moved the power wire to a hot terminal. I live just west of Chicago. I also just got done inspecting and cleaning the terminal box on the pass fender. Still nothing...Please help

[eddyj1]

I also cleaned the ground strap behind the rear panel in the hatch area

[Landseer]

I'd call roger at 928sRUS and buy the bmw "alternative" bosch crank position sensor (exactly same Bosch sensor and end, just a slightly longer cable). Cost about $60. Be careful removing the old one.

I'd also look closely at the MAF plug under the boot for shorted wire. You could also have a bad MAF. But change the crank sensor first.

Oh. Also, does it start if you jumper the fuel pump relay (30 to 87) and try to start it?

Did you look at the 16V grounds cleaning thread that I posted to be sure you got all the right grounds for the 84 Euro, which was my subject as well.

[Normy]

Isn't there supposed to be some sort of signal that goes from the starter relay complex and tells the computers [EZF and LH] that the engine is cranking and as such spark and fuel needs to flow?

N?

[Danglerb]

Originally Posted by Normy

Isn't there supposed to be some sort of signal that goes from the starter relay complex and tells the computers [EZF and LH] that the engine is cranking and as such spark and fuel needs to flow?

N?

Other way, on early cars green wire from sensor in distributor, newer cars its the crank position sensor CPS, the signal tells the brain the engine is turning, what speed, etc. and the brain decides what to do (turn on fuel pump, pulse injectors, etc.).

I've seen some cars with wiring attempting to bypass the alarm system running back to the fuel pump or starter, but best to remove it and put it back to factory arrangement and fix the real problems.

Fixing the previous owners fixes can be the real problem.

[Landseer]

Agreed.

There are early mafs that have a circuit that goes haywire and prevents the LH brain from energizing the fuel pump. A short of some of the wires at the maf plug might do that, too.


Alarm bypass is safe and easy at the CE panel with very little effort.