A few weeks back I'm taking my 88 five speed for a test drive after tweaking the steering wheel to pod squeak.

Drive over a bridge and the dies. Felt like I turned the engine off. Jumpered the fuel pump relay and I can hear the pump. Still no start.

Tow it home. Swapped relays and known good computers.

Break out my remote start button and test.

No fuel pressure. Cracked the fuel rail cap.
No injectors - per my noid.
No spark.

All that would point to a bad CPS.

I have a tach bounce and the tach moves as I try to start the car.

Brand new CPS - non Bosch - Facet.

I am mystified.

Picture of CE panel in case I have a relay where it shouldn't be.

 

you have 4 running relays,
check them as you turn on the key and as you crank then engine,
once you find the relay thats not clicking,
thats where to start.

 

Well, I've had no start with tach bounce that was indeed CPS. Am curious about non bosch version.

Other obvious failure point would involve checking valley grounds, and or any ancilliary short around there. Have had short, from wire twist degradation at MAF connector, take car completely and totally down, jadz928 perl S4, years ago.

 

Check that all the wires on the positive battery terminal are clean and tight.

The small wires that come off of the side of it power the computers, FP, etc.

Mine came loose on my 89 and caused a no start where it would healthily crank, but never get enough power to the computers to run.

It's always easy to check the dumb stuff first.

 

Fuel pump relay does not click - the other three click.

 

Did you put the known good computers back into another examplw and they still ran? ''

Double jeopardy is not likely to happen but with the LH never rule anything out unless and until it has been "double checked".

 

OK swap it with the horn relay,
retest.
You might need a Bosch CPS

 

Yes I checked my good spares in another 928 and it started.

The computers in the 88 have PEMs and were running until the car stopped running.

 

Roger that.

I'll report back.

 

No change with horn relay.

 

That being the case and the fuel pump relay was not being switched on narrows the field of culprits some and eliminates the CPS as a probable cause to my way of thinking at least. I use the same CPS at the moment albeit I rejigged the original after the male junior powertimer connector crumbles to pieces so I have that to fall back if needs be given I do not know the long term reliability of the alternate item. Stan has covered the relay so that leaves power up to the relay- check for power at relay terminal 30 and from the relay to the pump- a jumper across 30 to 87 will tell you immediately if there is a problem in this area if the pump does not power up if you have not tried that already.

 

Pump comes to life when I jumper it - at least it did when I started on this journey. I'll check again.

I checked the CPS to harness and it is clipped in.

Again - no fuel, no spark and no injector pulse - that points to the CPS - And yet the tach bounces and flutters when I crank it.

So interesting. It has to be something simple that accelerating over the joints on the bridge set in motion.

 

Have you got a scope to test the CPS signal? Testing at the CPS end and testing at the EZK plug connector end is relatively easy and show whether you have a viable signal [or not]. If I can do it anyone can!

Although the stock CP sensor male connector typically falls to pieces and the stock female connector is more resilient that could also be causing a connectivity issue if it is the original item as could degraded wires and this is a common problem with the wiring as it enters the connector under the boot. Some of mine were in awful condition ad somehow still seemed to work depsite the rot. Car felt much better after I revamped the loom.

FYI- Access to that CPS connector is a bear. When I revamped my harness last year I dumped the stock connection point and adjusted the ;ength of the loom so that I could sit it on top of the bell housing- now easy peasy to get at that connector any time I want and I used the modified junior powertimer connectors with the quick release clips.

 

Yeah I have the CPS harness end and CPS end out. I connected them and now I have no bounce. Great.

I'm going to inspect the harness end wiring and replace it and see if that helps.

 

I won't need an scope to diagnose the problem. I will to figure out how that happened.

What the heck did this?

It would have to interfere with something on the side of the flywheel facing the block.

That's just about impossible.

Actually it would be on the rear face of the flywheel. Still a mystery.