kmascotto

Please correct me if im wrong. The cps sensor turns on the LH which turns on the fuel pump relay, the current then goes through the fuel pump fuse to the fuel pump.

So, my engine had no fuel pressure, which i solved by jumpering the FP relay(30-87). Now I have fuel pressure...but the engine still will not start. so...im lead to believe my CPS is bad. I just put a brand new cps sensor on it. I don't have an oscilloscope to check the cps...

Could it be anything else?? what is the likely hood the LH in the issue? how can this be checked?

thanks in advance

kmascotto

By rights the engine should start when the jumper is in place even if the LH was the issue and not activating the FP relay. Is that an accurate assessment??

If so, I must have a bad CPS (even though its new)

dr bob

CPS is critical to the EZK operation to tell the sparks when to happen. The CPS signal goes to EZK for spark, also generates the tach signal there so you have a chance to watch for tach jumping as you crankthe starter. Tach signal is shared with the LH box, where its used to trigger the fuel pump relay among other things.

So do you see the tach move at all when you spin the starter? If no, the CPS is a possibility. If yes, then it's probably not your issue. If there's a question, test for spark. Induction timing light while cranking is non-invasive, otherwise a spark plug to ground should make a spark you can see.

Before you start tearing into things, think about those critical relay-relay-relays and the power that feeds them. Fuel injection, EZK and Fuel Pump relays are too-common causes of no-starts. If you haven't replaced them, do that now before getting any more tools dirty. Clean the aux positive connections at the battery too. Start with the easy-inexpensive-common issues first if you can.

kmascotto

Thank you Sir!!
I just did a quick check of the Tach bounce and there was no movement when the engine was cranked.
Tomorrow I will check the spark plug with my timing light and check all those relays...and those battery connections.
Thanks again!!

John Speake

While you have been fault finding, make sure you didn't put a relay in the kick down relay slot by accident. On an '89 GT that would be relay XV.

kmascotto

the update: I checked the LH, EZK and FP relays and all check out. I checked the aux wires at the battery and they are tight.

I hooked up my ignition tester to the plug wire and I have good spark.

So my CPS is not the issue...what are my next steps?

kmascotto

John, there is no relay in the kick down slot, so that's not it.

kmascotto

so the system is getting ignition but the FP relay is not being energized...but even when the FP relay is jumpered and the pump is working (there is fuel pressure) the engine still will not start. WTF

hwyengr

The signal for both the tach and the LH trigger come from the same pin on the EZK. If you aren't getting a tach bounce, it's likely the LH isn't getting a signal either. This is the point where an oscilloscope would come in handy so you can figure out where it's getting lost. If you've got a signal at the EZ, your problem is either in the harness or the tach.

kmascotto

Thanks hwyengr, I was thinking my next step is to check for continuity between EZH connector pin 13 to LH connector pin 1. I understand this connection is the trigger for the LH.

I guess if that line is fine...the only other possibility would be the LH computer.

Would that be a correct assumption?
thanks

hwyengr

Most likely, but not necessarily. The reason that the scope is used for this diagnostic is because the signal needs to have a certain amplitude to trigger the LH. You could have continuity between the pins, but a short to ground in the tach signal circuit could draw current away from the LH circuit dropping the signal below what is needed to turn it on.

Is this for your '89 or your '86.5? I'm more familiar with S3 circuitry, so that might not necessarily be the case for the '89.

kmascotto

Thanks again Jeremy, good to know.

Yes, this is for my 89GT...my 86.5 is perfect

John Speake

You would be able to measure the signal on pin 1 LH with a DVM as it is a 12v pk-pk signal. At cranking speed you should be able to measure on dc volts range.

kmascotto

Thanks John, i assume the purpose of this test would indicate that the EZK was sending a signal to the LH, and the signal was strong enough...correct?

kmascotto

latest update:

I tested the continuity of the EZK connector pin 13 to LH connector pin 1 and we have connectivity.

I tested the LH connector pin 20 to FP relay 85 and we have connectivity.

I tested the LH connector pin 4 for 12 volts, it has power

I tested the continuity from LH connector pin 21 to LH relay pin 85 and we have connectivity.

I tested the LH pin 18 for 12V after jumpering the LH relay, and that works too

I tested the voltage (DVM) on the LH pin 1 when the motor was being cranked and there was power.

So....any other suggestions or thoughts??

thanks