Ninespub

Tampa 928s. Thanks for your reply and the old threads about your similar problems last year. However......On neither one did i see a "resolution post", that is to say: "I found it! I found it! I really, really found it". In other words, what finally solved your issues! Inquiring minds want to know. Looking forward to your answer.

Paul Barrera '91 $$$$$4

Tampa 928s

Well the bottom line after replacing the Inj connectors it ran then stopped than ran it was the following.
Bad Inj ground from the LH pin they were spread just a little, that caused it to go on and off. The Inj are pulsed by this pin the 12v stay on all the time when running.
The thing about the Injectors is that they are all in parallel and cannot be tested if a short is present.
If you can pull the rear inj off and check for 12v that will tell you is your getting power, this will stop a lot of looking for 12v firing issues.
As far as the ground testing the only way is to remove all the injector connectors , remove the computer connections and Ox sensor wire and measure for a short from Pos to Neg on any connector.
It's a small chance you have a shorted Inj but you can test while off it should read around 16 ohms.
Also go from one side on the connector to the appropriate pins to check for continuity to the computer connectors.
Hope this helps.

Ninespub

Tampa 928s. Mucho thanks, again, for your reply. DaveK, who is trying to solve the issues with my '91 has tried like hell to source the problem with the help of Andrew O. and many other Rennlisters like your self. Sometimes the simpilist process (as you know) can wreak havok for weeks and everybody's experience makes the difference. I know he'll see your posts.

Paul Barrer '91 $$$$$4

Peter F

Paul,

have the MAF connector been checked yet per my post from Dec. 30.
It took me almost two years of intermittent cut outs very difficult to measure.
It was not found until the MAF connector boot was cut open.

Good luck/Peter

AO

It is not that MAF. The problm is there is a lack of signal to the injectors. The MAF would not cause this. When it runs, it runs fine. I still think it's either a harness issue or the alarm.

davek9

Hi eveyone, well back at it once again after doing 12 hr's last night at work.. oh well it's better than not working (been there).. anyway I was wrong about my first look at the signal on W11, that pic I posted was an example of a BAD signal that was either being held down or weak.

Here is another look, first is the bad it looks high only because the scope sensitive was cranked up, in an effort to see something. It needs to be set ~.5 v/div (1/2 volt per division).

The second Pic is a Running signal, looks to be ~ 3.0 v P to P (3 volts peak to peak).

Well the car is running right now, actually I can not make it fail (I could), I have tried pushing and pulling on connectors and wires all over the car, not even a miss,
starts right up and runs smooth.

Any suggestions on what to check while it is running..?

Also I received some PM on how I built the Voltage Divider, it’s almost pictured here to the left of the PC, I built it in a small project box that I got at the local Radio shack. I’ll do another post later on.

Thanks Davek9

John Speake

So the top picture is a cranking signal, with less that 1v p-p ? That is rather low...

The second pic is fine.

davek9

That's correct John, < 1.v p to p, at W11 (looks like a slight bump if scope is set @ .5 vp to p) when it does not start, something is/was holding it down or the source failing.
I'm Looking for some trace points for when it fails again, as today it is running fine.

Thanks DaveK9

Ninespub

IT.....IS......ALIVE! Great work Dave! Do you have any idea what the problem was/is?

Paul Barrera '91 $$$$$$4 - yeah, the one DaveK's been working on.

AO

Winter.

Ninespub

Andrew, winter is over! Spring started a week ago and all of God's little creatures (like furry little rabbits and SKUNKS) look for a new crib so they can hook up and make new ones. They love decks and porsches, I meant porches!

Paul Barrera '91 $$$$$$4

davek9

I have not fixed it yet Paul, "it tasks me.."
But I will..

Z

The signal at W11 is the tach signal as provided by the EZK to the LH, tach in the dash, and the kickdown relay in A/T equipped cars. It's not the same as the crank sensor signal that goes into the EZK. A good signal at W11 will tell you that the EZK is getting a good crank sensor signal, and that the EZK is putting out a good tach signal that the LH should be recieving if there's a good wiring connection between the EZK and LH though.

davek9

Thanks Z, now if would only fail again.. it's been running great all week! Starts right up and continues to run.
Z, any accessible test points that I might be able to use to solate this if the signal goes south again?

DaveK9

Z

The signal from the crank sensor could be checked by disconnecting the EZK plug and connecting the oscilloscope to terminals 6 and 23. Terminal 6 is the negative, and terminal 23 is the positive from the crank sensor. Crank the engine and the wave form you should see is shown on page D 28-11 of the shop manuals. If you get a good signal there on the occasions when the car won't start, reconnect the plug to the EZK, disconnect the plug from the LH, and connect to the LH plug terminals 1 and 17. Terminal 1 is positive and terminal 17 is ground. Check there for that same signal that you got earlier in the thread at W11. If you get a good signal at those EZK 6 and 23 terminals but nothing at the LH 1 and 17 terminals, the issue is with the EZK or the wiring coming out of it that supplies the tach signal to the LH.