jtischner

I recently had the S300 chips installed with a new 87 fuel regulator and x-pipe exhaust. After picking up car from the shop, the car was having starting problems. that is, it wouldn't start on the first turn of the key. Once started the car drove normally. The last time the car started it struggled again, but finally did start. Drove it home, parked it for a week or so, tried to restart and nogo.

Engine turns, but no spark.

Things we've tried/repaired:

1) Fuel pressure is good - after changing burned fuse for the fuel pump
2) Changed relays IV, XIV, XVI - no spark
3) Check spark plugs - no spark

What else can I check ?

Note: The car had no starting problems at all prior to the S300 chips being installed.

Thanks.
Joe Tischner

John Speake

The fuse/relay cvhart on the 928Specialists website gives the EZ-F relay as XXII, the fuel pump relay as XXVI and the LH relay as XXV......

I would change the EZ-F relay first, if that is OK then inspect the CPS and its connector nearby.

How did you check fuel pressure when you say there is no spark, the fuel pump isn't energised if the
EZ-F isn't working.

Shark Attack

Wires to the coil? I'd put the old chips back in and see if the issue goes away. If it does call whoever made the chips.

PorKen

The CPS (crank position sensor) plug may have disintegrated when the FPR was installed, if it was original.



The EPROM socket on the EZF motherboard is easy to loosen or pull out of it's solder joints if the stock chip is not removed carefully.
This can cause cutouts while driving or hard/no starts. It can often be diagnosed by rapping on the EZ case with a rubber mallet while idling.

It is a 'simple' fix, just reflow the solder on the 24 pins.

Is there someone nearby that can loan you a EZF box for test drive?
The ignition chip can be stock for testing.

MGW-Fla

Hey Ken,

I have your chips(luv the improvement), '87 FPR, & hotter plugs, in my '85. None of the other suggested improvements yet, plan to get the MAF recalibrated. Its mostly becoming a DE car & I don't drive it much otherwise. Since changing things out earlier this year I've noticed a difference at times when cranking. Sometimes instead of cranking right up as in the past, it wants to cut out right out, stumble and/or surge. Its random as to when it does it, but enough to cause me to question whats going on?

Just wondered your thoughts on the surging/stumbling/cut out starts & whether the CPS could cause this? Thanks!

Don Carter

I'm near by and have been working on the issue. We put a fuel rail gauge on it, had zero pressure at first, then replaced a melted fuse and got the expected pressure in the low 50's. I used a timing light to check spark but also pulled a plug wire and checked spark that way.

On the next visit, I had planned to check spark on the other ignition circuit, inspect coil wires, check grounds, especially near the front bumper next to the exciters, or whatever they are called, and near coils, inspect CPS connection, red wires near battery, etc...

Haven't looked at or pulled the chips yet.

Definately welcome more ideas and input.

Don Carter

John,

The 928Specialist relay diagram shows XXII as "Reverse Light Relay (Auto)
" and XXVI as "Not Used". We did swap out the EZ-F relay (XXV), but will probably check them out again.

The big mystery to me on this is we found and fixed a fuel problem, then had no spark. Not likely to have two failures at the same time. Something strange going on.

John Speake

Hi Don
This was the chart I referred to..... for MY85/86
https://www.928gt.com/t-8586fuse.aspx

But it appears to be incorrect. Tech book gives EZK XV1 ; LH as XXV and FP as XX

WyattsRide

Could it just be that the battery is old and not strong enough anymore? Or a bad/corroded ground strap?

A friend's 928 sat for a long time. He tried to charge the battery. Interior lights came on, engine turned but wouldn't fire. Put in my known strong battery and boom, fired right up.

Don Carter

Joe and I spent some time looking at the car this evening. We didn't get it running but may have found the problem.

The most likely suspect is the CPS connector. It's of course crumbling and was zip tied together at some point. It's hard to see in the pic, but there are bare wires on both the yellow and blue as they enter the black insulation, and I think they are probably shorted together. We didn't tear into it any further, but on the the drive home I was wishing I had cut back some insulation to get a better look.



Some other observations....

- Verified that the 928GT relay chart matches the original chart that came with the car.
- Verified new relays installed in
IV - Ignition
XVI - EZF Ingintion
XXV - LH jetronnic FI
- Verified no spark on either ignition bank at spark plug wire with timing light
- Verified battery voltage at coil (11.5v)
- Cleaned grounds near amplifiers, and near coils
- Checked red wires near battery, all looked ok
- Ground strap doesn't look great, but probably wouldn't cause a no spark issue
- Battery voltage is 11.5v, this is an issue since it had been on the charger all day. We put the charger back on, and set to start mode (50Amp) to get the voltage up over 12, and it still wouldn't start.
- There's also an aftermarket alarm and a mess of wires that goes with it around the CE panel.
- MAF plug and wires look ok.

I'm suspecting the CPS plug at this point, and it needs to be fixed even if it's not the cause of the no-start.

Any other ideas?

Mrmerlin

how does a part this important even stay in the car?
replace the CPS obviously

Don Carter

Stan,

The crumbling plug and possible short is on the car side, so thinking we should fix that first and see if solves the issue. Replacing the CPS would make sense if that doesn't fix it.

Mrmerlin

Roger has a repair connector and a new CPS.

BUT

FWIW from the condition of the connector it might be wise to be on the lookout for a new engine harness.

My 86 was suffering from a fate similar to this ,
the PO had so many running issues he sold the car due to failures that would come and go.
Swapping in a new good condition used harness , first turn of the key the car ran perfectly.
NOTE the CPS had also been replaced and the car side connector looked similar to yours.
The MAF unit also had failing shorted wires in general a big mess

Don Carter

Yes, I told Joe last night Roger probably had the replacement plugs. Joe also needs a few other maintenance items such as MAF o rings, so he'll be placing an order soon. Also suggested the fuel lines need replacing.

Mrmerlin

it should also be investigated to follow Kens suggestion for checking the computers and reflowing the connections see post 4

MGW since you quoted part of post 4 ,
reread it and follow Kens suggestions