Can anyone give me a run-down of the symptoms of a failing CPS?

I've decided to sell my 240 and wouldn't you know that when someone is there to see it, it refuses to start. Quite embarrassing. At least in this case it was two Brickboard members who were not overly concerned about that issue, and had already decided not to buy the car anyway.

After running in the AM and PM, it began to snow heavily and while the car was under shelter it steadfastly refused to start for the rest of the night and the next day until it suddenly started to work again. It is much drier now, but still cold.

I tried to use the diagnostic block. The only thing I get is with the Pin is the #6 hole, the LED shines brightly. No flashes to decode.


The insulation on the CPS *is* failing, but there are no exposed metal wires that I could see. I've jiggled the CPS wiring, repositioned it, removed and reconnected it, and none of these thing made a difference in the starting or running condition. After it was running I played with the wire some more and could produce no change in the running condition. In the fall, I was able to make it stumble a little bit by pouring water down the firewall.

Is there anything else I could be missing? I've confirmed fuel pump function and fuel at the injector rail. I've not been able to confirm spark pulse yet, but now that the car is running again, I'm not sure it would tell me anything.

I can diagnose and solve a complete failure, but this intermittent, time/atmospheric-linked problem is very hard to figure out.
This is driving me nuts!

When mine went bad, it never got to the point that the car refused to start. When starting up from cold, the engine would run fine for about half an hour. When thoroughly warmed up though, the engine would occasionally miss for a couple of seconds, run fine for a while and then miss again etc. The way I understand it, this is a typical way for a semi-conductor to fail (they apparently tend to fail intermittently at first, and particularly when warm).

I replaced the CPS and the problem was solved.

Good luck with it,
Erling.
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I tried to use the diagnostic block. The only thing I get is with the Pin is the #6 hole, the LED shines brightly. No flashes to decode.

There is the key to the problem. Focus on this, or maybe explain it in more detail so we know exactly what you mean.
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Art Benstein near Baltimore

How to Ask Smart Questions

I seem to think that the #6 pin is for ignition problems. Which could still point back to the CPS... I'm going to give it a proper tune-up (new cap, rotor, wires) before I move much further.

The single led without flashing worries me that the block needs cleaning to bring it back. The thing was open and the cover was down in a body cavity when I got the car, so who know what kind crud/corrosion got into the unit.

It is pretty cold/dry here which makes outside work unpleasant, but I'll continue to chase out the issue.

Thanks

Yes, the #6 pin is for the ignition system. Doing a "tune up" won't affect what the OBD is telling you, which is, the ignition computer is dead.

But as you suspect, it could just be the OBD pin 6 terminal that is dead, so by all means pull that apart and shake out any dirt clogs and spider webs, but consider it may be reporting honestly.

The single led without flashing...

If that means the led comes on when, and only when, you push the button, given the probe is in #6, given the #2 reports codes, and given the ignition key is on... then your EZK ignition computer is dead. Since those computers never die, it probably means it just lacks power. Test for power at the large red lead going to terminal #30 on the fuel relay, or more convenient under the hood, check power at the orange wire on the AMM with key on. The usual cause is corrosion at the 25A blade fuse holder or its wiring near the battery.
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Art Benstein near Baltimore

Since it's the early worm that gets eaten by the bird, sleep late.

Art, thank you for the detailed reply. I've already ordered a new CPS, but your suggestion that the fuse holder might be the problem is consistent with my observations. I only recently discovered the fuse. The holder has come lose and was laying on the inner fender hidden by wiring. I'm considering ordering the IPD fuse holder kit just to take that issue out of the equation.

Tomorrow, Ill see if I can sort out the computer.

Any codes in the #2 position?
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Did you check for fuel when it didn't start? It sounds to me like a failing fuel pump relay. Last summer my in-law's stopped in my driveway. When mine went it was more intermitant for a couple of weeks first. I picked up replacement at NAPA last summer for about $35.

Mark

When it wasn't starting, I swapped out the fuel pump relay with another spare. I've also tried that in the past when the problem only appeared rarely. It doesn't seem to make a difference.

Also when it wouldn't start, I opened the fuel rail and confirmed pressurized fuel in the line. I should have had some sort of starting condition if there was pressurized fuel behind the injectors.

I'm thinking that the injectors are not firing, or the sparks are getting no pulse from the dizzy. I'm not sure what precise symptom the CPS would cause when failing so I've not been able to narrow down the testing parameters yet.

And now that the car is starting and running again, it will be nearly impossible to diagnose.

What I can see for sure is that the problem has gradually become more frequent. I'm assuming whatever it is, is something that can fail intermittently and become more frequent. My past experience like that was a failing RSR on a rex/regina 740. I don't think the 1990 240 has one...

Wow, My first thoughts, like yours, would be Fuel pump relay and then Crank Position Sensor. You obviously changed out teh FPR without success.. So that would lean a bit toward the CPS the fact that you could wiggle it around while teh car was runnig and not get it to act-up surprises me.
The fuel will pressurized just from turning the key.. It is after that that the CPS will stop running the pumps if it sees no cranking.
I know you are selling it but if the insulation on the CPS is already split maybe it's wise to make it right.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html

Thanks, that is what I was wanting to know. So the CPS will kill the pump when pressure has reached normal in the pump? interesting. I wonder if I hot-wire the pump (jumping the fuses) would the thing run? Hard to say when it is working fine - but maybe a worthy test when it failed next time.

I've actually de-listed my local advertisement for the car, but I'll leave the BB and IPD ads up a while longer. I'll re-list it when it will start reliably. No point scheduling people to see it when it won't run. I'm giving it a proper tune up and after I solve this stalling issue, I may re-list it or decide to keep it.

My thought on the CPS is that the sensor is going bad down on the bellhousing side - might explain why moisture down there causes problems, and why can't cause or fix the problem by fiddling with the wires.

The main problem there is that I cannot see the CPS or see a way to it easily so I can't check the condition or test it for problems.

Any advice on how to get to the CPS? I know it is bolted to the top of the bellhousing, but unlike my 940, I can't see how to get a socket extension down to it. Do you have to come at it from the back after lowering the transmission? I hope there is a simpler approach.

"So the CPS will kill the pump when pressure has reached normal in the pump? interesting."

No. Tony is mistaken on that. Below is a canned post where I try to explain the relationships between the main players, beginning with the CPS.

I'd say just put a new one in.

=======(canned post)==========>

Start-Run Sequence

1) During starter cranking, the Crank Position Sensor (CPS) sends timing pulses to Ignition Control Unit (ICU)

2-a) The ICU uses these CPS pulses to trigger the Power Stage (aka Ignition Amplifier), which triggers spark from the coil.

2-b) At the same time, The ICU also propagates the pulses to the FI ECU, to allow FI operation.
==>(no ICU pulses means no FI operation)<==

3-a) The Fuel Injection (System)* relay (previously energized at Key On) powers the AMM, IAC, ECU, Injectors, and the Fuel (pump) relay coil + side.
* The System relay is in the white case with the Fuel relay.

3-b) When ICU pulses are received by the FI ECU, it "energizes" the Fuel relay by grounding the relay coil (– side) to run the fuel pumps.

When all these things work, the engine runs until the Ignition is switched off, which in turn shuts down the FI system.

<============(end canned post)======

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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

After you stumble through it once, it's easy. But the first time is tough.

On my '89, the AC crap is not up on the Passenger Fender by #4 cylinder (I think in '90 it is) so I can sneak my hand under the Exhaust manifold and under the Hard pipe for the Heater hoses and get on the one 10mm bolt with a Box wrench.
A 12" extension ( or 2) and a Socket with a 'U' joint attached will get you on it from the Passenger side as well. The swivel joint on the socket is the Key.
There is many writeups if you do a SEARCH.
You do not have to do this from under the car at all. After the Bolt is out, take your time convincing the CPS that it wants to come out of the bracket, Many people have a problem where the CPS is stuck. If you muscle it and break the bracket THEN you will be dropping the trani to replace the bracket.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Thanks. I've got a fine-quality swivel socket, some freakin' long extensions (purchased to do the CPS on the 940). I've just ordered a replacement CPS, so I'll plan on fixing it next week.

In the meantime I'll try and get the diagnostic module to return some codes.
So far, I get nothing at all from #2. Just the solid LED from #6. pretty weird.

I ran into a bad CPS with a friends car about a month back. No signs it was going to fail until it just wouldn't start. Felt bad since my friend usually only drives a couple miles to work but this time it failed while 50 miles from home.

I found a used one off a 740. Where the CPS connects to the harness there should be a white band around the wire. If it doesn't have that band then its the original one. I'd replace it either way. You might get lucky and find a used one for under $10 like I did. Easy to install and if hasn't been replaced you might as well to eliminate it from the possibilities for the no start.