hans14914

I have a friends early 87 here with a no-start problem. I told him I would take a look, assuming it would be something simple. It may still be, but figured I would post it out to the experts.

The car cranks hard, but there is no tach signal at the dash. The CPS is new, and it tests out fine all the way the EZK connector. EZK connector also tests fine to both permanent and switched power and ground.

I pulled the airbox to take a look, and the MAF connector is shot. I am ordering a replacement on monday and will get that fixed. Could a shorted MAF connector cause a no-tach and non-start?

MAF connector needs to be repaired, and will do that when I get back from SITM, but any ideas why it wont even start in a limp mode? I am a bit gunshy to toss one of my EZK in their with the possibility of a short through the MAF harness until I fix that.

Thanks,
Hans

John Speake

Is there a spark ? That's the first thing to check. If there's no output from the MAF, then the car should start easily in limp home mode. If there was a power short on the MAF connector, then that could cause other problems, but not a no tach reading while cranking...

dr bob

Basic troubleshooting includes a test for spark using a spark-gap style tester in an ignition lead, or an inductive timing light for a non-invasive but less definitive test. A 'noid' light for fuel injection pulses, and a fuel pressure gauge to test for, um, fuel pressure.

Most fail-to-start conditions are caused by stupidly simple things. Cars are out of fuel. Bad aux battery connections or discharged battery. Relay-relay-relay (FP, LH, EZK). No fuel pressure. Then we get to move on to sensors and controllers after the basic causes are eliminated as possibilities. In my limited experience anyway.

hans14914

Sorry for the late follow-up. I did test spark before posting and there is spark from both distributors . EXZ seems to functioning as normal.

The LH is not energizing the fuel pump.

I do not have easy access to my o'scope, so using both a frequency counter and AC voltmeter I do see a signal (although weaker than the native output of the CPS) both at the W CE Connector and at the LH connector.

That is one reason that makes this so strange.

I am ordering the MAF connector this morning, and will replace that when I get back from SITM. I think I will also pull the CE and go through it and look for any signs of trauma.

Inspection of the engine harness looked decent except for the MAF, and the basic sensor impedance and supply voltages all check out.

Its a head scratcher for sure.

John Speake

It's the signal at pin 1 LH that is critical, that is the signal that wakes up the LH when the engine is turning. You can check it with a voltmeter in a.c. volts, depending on the time constants of your meter you should measure about 4v rms.

hans14914

I recall it being less than that, but will check. There is a measurable signal there though, and at that W block. Will report back if its the full 4v though.

If not, thoughts on how to diagnose? Impedence between the EZK plug and LH plug? My assumption is it should be negligible, and any resistance implies a failure in the harness.

Thanks
Hans

John Speake

The actual reading will vary, depending on the time constants (filtering) in your meter. The signal is a square wave, and the meter on a.c. volts is calibrated for a sine waveform. If it indicates several volts, then probably OK.

Lizard928

Hans,

The EZF/EZK gets the rpm signal from the CPS, it then sends a calculated RPM signal to the LH. This signal is tapped in to and goes to both the kickdown relay (auto), and the tachometer.
I've seen a couple defective tachometers which corrupt the signal going to the LH which then creates a no start situation.
To test this, go to the CE panel W plug and remove pin W11. Put a protector on it and verify that it cannot touch anything else (ground or power).
Once this is done nothing can interfere with the tachometer. If the car starts, remove the kickdown relay and reattach that pin. If that doesn't correct the problem, then the tach is dead.

Hope this helps.

Bill Ball

Hans:

You're plenty smart, so this may seem like underestimating you, but I'm just going to say this because you haven't provided the direct evidence that the LH is not energizing the fuel pump....

Does the car start and run if you jump the fuel pump relay? If energizing the pump is the core issue, it should (unless the LH has failed).

For no-starts with good cranking I generally start by jumping all 3 relevant relays, because as we learned long ago from Jim Bailey, it's relay, relay, relay. You've got spark, so you can skip the EZK relay.

Then I swap in a spare LH simply because it's easy (if you have a spare or cans swap the LH in question into another S4/GT/GTS) and LH failures are common and that would account for your lack of fuel pump activation, although I haven't seen an LH failure do just that.

If you can at least make sure there are no shorts in the MAF plug or cut off the plug (since you are replacing it anyway), the car should start and run, although not well as you know, if the MAF plug is somehow involved in the problem.

These are shadetree techniques that often find the problem. If you have good spark, then fueling is going to be the issue. It may be something exotic, like a bad tach, but rule out the common stuff first if you haven't already (I suspect you're going to tell us you already have).

My trusty car died on the freeway a week ago and would not start. After I got towed home I had no luck with the above. Then I loosened the cap on the fuel rail expecting fuel to spray out under pressure and got only a few drops. The fuel pump ran well with the jumper wire in the fuel pump relay, but still there was no substantial fuel at the rail. The fuel pump was only 3 months old, but it had failed. Argh! I had changed it out because I was still running the original fuel pump after 266K miles and thought it would be a good idea to replace it before it failed on me out in the middle of nowhere. Foiled again!

worf928

I assume you checked the fuel pump fuse?

Has there been any recent work on this '87? What was it?

Has anyone been near the two ground points at the rear of the block?

hans14914

Thanks all, while the tach issue sounds far fetched, its the most plausible thing I have heard so far, and will test that when I get back from SITM.

This car happens to have a fuel pressure gauge on the rail. The LH certainly does not energize the pump, but jumpering the pump does get normal operating pressure. There is measurable voltage, both at the W connector and the LH connector (need to try pulling the tach feed). All the power and ground feeds test out at the EZK connector (need to trouble shoot the LH harness further). Swapping in a good LH has no effect.

It certainly isnt any of the normal failures modes that you can identify quickly.

I am going to really dig into it next week when I get back. I am pulling the CE, and will take a look to make sure there are not any rodent related issues. I have seen that on other cars before.

Thanks for the advice guys!
Hans

Bill Ball

So, jumping the pump relay gets fuel pressure but the car still does not start despite good spark, right? That suggests the injectors are not firing. I would swap the suspect LH into your car and see if the fault follows. If not, then investigate the injectors. A noid light would verify whether the injectors are firing. If not, then it's likely one of the injector plugs has a short. A short in any one plug will prevent all injectors from firing. It's common the find wires inside one of the injector plug boots to be twisted and shorted.

hans14914

It could be an injector short, but I would assume the LH would still energize the pump?

Swapping in a different working LH has no effect. Seems as though it doesnt see a valid pulse on pin1, but I can measure it with a DMM.

Will get serious about it next week, possibly pulling out the o'scope. I will test the LH harness first according to the manual, but it is one of the most curious non-starts I have ever run into.

andy-gts

hmmmm what ever happened ????

hans14914

I found a bad crimp from the factory on a terminal in the W connector. Blob of solder fixed it temporarily, but ordered some new terminals from Roger. Think this one is back on the road.

Hoping to shake it down tomorrow afternoon.