When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
From JDS Porsche...
Quote:
A modified version of the rpm signal is fed from the EZK to the LH ECU (and also the rev. counter). When the LH (fuel injector ECU) receives this rpm signal it will energise the fuel pump relay. The rpm pulse also times the injector signals from the LH ECU
The full quote from JDS Porsche:
All LH equipped 928s operate on a similar principle - a sensor (flywheel speed sensor) detects engine speed and crank position from a toothed gear at the rear of the engine. The flywheel speed sensor output is fed to the EZK/EZF (ignition) ECU. This gives the EZK the information it requires to time the spark.
A modified version of the rpm signal is fed from the EZK to the LH ECU (and also the rev. counter). When the LH (fuel injector ECU) receives this rpm signal it will energise the fuel pump relay. The rpm pulse also times the injector signals from the LH ECU. Information on engine air intake mass (load) comes from the MAF (mass airflow sensor. From rpm and laod data, plus engine temperature and other sensor paramters, the LH ECU determines the correct fuel injector opening time.
4) If there is spark, but no start, then check that the fuel pump relay is being energised when the engine is turning. Alternatively, you can "jump" the fuel pump relay. But take great care to link the correct pins on the relay socket, or damage can be caused to the LH ECU. (emphasis mine) The contacts to be linked are 30 and 87. When these are linked, the fuel pump should be heard to run, even with the igntion switched off. If the car now starts, then remove the link and fit a known good fuel pump relay.
Post #90
So, if the LH isn't getting an RPM signal after 1-2 seconds, it shuts off the fuel. The only place the LH gets an RPM signal is the EZK. The only places the EZK gets an RPM signal are the crank sensor and the hall sender.
The crank sensor output is used by the EZK for the signal to the tach.
There is a white/red wire that goes from EZK Pin 26 to LH Pin 1. This is the signal from the EZK.
From the 'Test Plan, LH and EZK' in the CD Set:
If you see that signal and the FP relay doesn't pick up, then it's the LH. If you don't see that signal it's either the EZK or the Crank Position Sensor or connecting wiring.
I think someone mentioned that the CPS plug crumbles with age and temperature. Maybe look at that.
Could the fire up and stumbling be an intermittent CPS signal? Fuel and spark for the first 2 seconds, then occasional speed signals that keep things rolling.
Great! thanks for the review. I was just on the phone with rich and he mentioned the same thing. .... so in reviewing it all in my head, I'm wondering how the fuel pump relay gets that 1 second signal too. you know the one that turns on the fuel pump to pressurize the system when you turn the key? is that the same signal that is generating via the RPM signal? he also said it was pin 13 on the EZK going to Pin 1 on the LH and that should be checked for continuity. Ill have to pull out the diagrams, but just wondering about that. the fact that I can only get fuel via jumping the fuel pump relay, and there is no tach signal , sure points to the LH ether being bad or the LH not getting power.
Originally Posted by hb4
From post #26:
The full quote from JDS Porsche:
Post #90
There is a white/red wire that goes from EZK Pin 26 to LH Pin 1. This is the signal from the EZK.
From the 'Test Plan, LH and EZK' in the CD Set:
If you see that signal and the FP relay doesn't pick up, then it's the LH. If you don't see that signal it's either the EZK or the Crank Position Sensor or connecting wiring.
I think someone mentioned that the CPS plug crumbles with age and temperature. Maybe look at that.
Could the fire up and stumbling be an intermittent CPS signal? Fuel and spark for the first 2 seconds, then occasional speed signals that keep things rolling.
I'm wondering how the fuel pump relay gets that 1 second signal too. you know the one that turns on the fuel pump to pressurize the system when you turn the key? is that the same signal that is generating via the RPM signal?
The LH has logic circuits. One of them figures out when the ignition switch goes from 'off' to 'on' and sends a fuel pump signal for 2 seconds. Another one monitors the RPM from the EZK and sends a fuel pump signal if the crank is rotating. They both implement their logic by pulling LH pin 20 to ground. So, yes.
I had to blow up the WD to 400% to see what I thought was '1', was a '3' this morning, so yes, pin 1 to pin 13, not 26. Sorry for the error.
the fact that I can only get fuel via jumping the fuel pump relay, and there is no tach signal , sure points to the LH ether being bad or the LH not getting power
Is there some reason why you don't think the crank position switch or its wiring to the EZK could be faulty?
The LH has logic circuits. One of them figures out when the ignition switch goes from 'off' to 'on' and sends a fuel pump signal for 2 seconds. Another one monitors the RPM from the EZK and sends a fuel pump signal if the crank is rotating. They both implement their logic by pulling LH pin 20 to ground. So, yes.
I had to blow up the WD to 400% to see what I thought was '1', was a '3' this morning, so yes, pin 1 to pin 13, not 26. Sorry for the error.
Is there some reason why you don't think the crank position switch or its wiring to the EZK could be faulty?
Thanks Bill! actually, the crank pos switch is in the back of my mind... but would that wouldn't cause the fuel pump relay to not be "primed" for 1 second via the LH..... as nothing is spinning yet. but as it spins we dont have a RPM signal, so the sensor or the LH? if the LH isnt getting power, I dont think those injectors could flutter like they did, right?
also wondering about why the fuel pressure decay? is that going into the cylinders or back to the tank via a faulty check valve? either way, that's a side issue, unless there is a shorted injector that also is causing a problem for the RPM signal circuit. the funny thing about that little issue, was that after the injector flutter episode, the pressure remained constant and didnt decay. (first time that has happened) then later, with a key turn and start attempt it went back to its old antics.
as far as wiring.... i was told that pin1 on LH was a shared ground with pin 13 on the EZK, so that i was to get a continuity meter on those two pins, true?
Thanks Bill! actually, the crank pos switch is in the back of my mind... but would that wouldn't cause the fuel pump relay to not be "primed" for 1 second via the LH..... as nothing is spinning yet.
Again:
IF (less than 1 second after ignition on) THEN (energize FPR)
OR
IF[(greater than 1 second) AND (RPM signal)] THEN (energize FPR)
RPM is not involved until after 1 second (or whatever that time is).
but as it spins we dont have a RPM signal, so the sensor or the LH?
yes
if the LH isnt getting power, I dont think those injectors could flutter like they did, right?
Beats me. All I know is that if they flutter, then it can be a bad LH. Ask Rich.
also wondering about why the fuel pressure decay? is that going into the cylinders or back to the tank via a faulty check valve? either way, that's a side issue, unless there is a shorted injector that also is causing a problem for the RPM signal circuit.
I'm not touching the fuel pressure issue; beyond my pay grade. I seem to remember a comment that a shorted injector can affect the LH logic, so since the RPM signal is processed by the LH then, yes.
as far as wiring.... i was told that pin1 on LH was a shared ground with pin 13 on the EZK, so that i was to get a continuity meter on those two pins, true?
There's a wire from EZK p1 to LH p13. It's identified as the RPM signal, EZK to LH. So, not a ground. You should see continuity (virtually zero ohms) between them, i.e. checking the wire, but not necessarily each one to ground. It looks like the EZK gets its ground on p18.
Again:
IF (less than 1 second after ignition on) THEN (energize FPR)
OR
IF[(greater than 1 second) AND (RPM signal)] THEN (energize FPR)
RPM is not involved until after 1 second (or whatever that time is).
yes
Beats me. All I know is that if they flutter, then it can be a bad LH. Ask Rich.
I'm not touching the fuel pressure issue; beyond my pay grade. I seem to remember a comment that a shorted injector can affect the LH logic, so since the RPM signal is processed by the LH then, yes.
There's a wire from EZK p1 to LH p13. It's identified as the RPM signal, EZK to LH. So, not a ground. You should see continuity (virtually zero ohms) between them, i.e. checking the wire, but not necessarily each one to ground. It looks like the EZK gets its ground on p18.
got it.... thats right about the EZK pin 1... confused that with the brownwire from the fuel pump relay top socket terminal. (that was ground) .
I think i have enough to go on.. interesting that the shorted injector maybe causing logic issues in the LH.... that sounds like that could be the issue.
we are not getting the fuel pump relay to energize, either for the 1 second or the running portion. one is unrelated to the crank sensor, and both are related to the LH. I guess he could blindly replace all injectors or somehow put a meter on all of them and see if they are working or have the right impedance. ill start with continuity check for the RPM signal , then the square wave check for the pin 17 for RPM sensor.
also , checking the CPS as that could also be an issue, maybe even more if its shorted internally.
Also, EZK p13 is brought out to the Diagnostic Connector, Pin 3. That should tell you whether the EZK is transmitting the RPM signal to the LH, if you have a Hammer, Sharktuner? or Theo's tester.
Also, EZK p13 is brought out to the Diagnostic Connector, Pin 3. That should tell you whether the EZK is transmitting the RPM signal to the LH, if you have a Hammer, Sharktuner? or Theo's tester.
so that little lone black 4 pin connector that floats around has a pin on it that (pin3) that is the same as pin 13? isnt pin 17 to pin 1 on the LH the RPM signal?
also we jumpered (well he did) the relays.... all of them (ezk, LH and fuel pump) and the car tried to start but no go.... same as before. however, when he did jumper the sockets, there was a periodic "click", click click. in the injectors , from what he saw and heard. sounds weird.. .... there should be nothing that is clicking when those relays are activated by the ignition.
I think its pointing to the CPS.. but it looks fine and wire looks fine that goes to it.... cant find my oscilloscope or anything that can check this... what about the AC voltage function on the meter, can that approximate a reading from this? or does it has be something that can measure a square wave?
No, but we sent the brains to Rich, who verified they were good. sounds like they might not be.........I dont think i want any of my brains touching this car. sorry, just too risky for me. (scared of the unknown... not my expertise)
Trying his brain in your car has little if any risk......
Trying his brain in your car has little if any risk......
thats good to know.... then, it might be something to try... i think there is some funny stuff going on in the injectors.... all that clicking! plus, Rich took his brains and drove his car around and it ran fine. CPS? short in the injectors? those are the two things im thinking at this point... man this is frustrating.
RPM signal goes from EZK p13 to LH p1. There is nothing connected to EZK P17.
The diagnostic connecter is a 12-pin connector near the LH/EZK on an '88.
The WSM says use an oscilloscope to measure the square wave on the wire from the EZK to the LH; an AC voltmeter will not read the correct voltage, but if there's voltage there I'm pretty sure it would show something.
ok folks, we got a oscilloscope to see if there is a square wave output from pin 1 on the LH box to Pin 17 (ground) on the LH box connector, when that connnctor is disconnnected (and ezk is connnected and the car is turned over)
just a little blip, no square wave, looks like no signal is going through it. I wasnt doing the testing, but someone with the scope was. doesnt look like the CPS is producing anything.
they also put an ohm meter on the sensor and found 160Ohms resistance. does that sound right ? (between 17 and 1)
this could be it, but hard to imagine the sensor being all of the sudden, bad.
06-22-2015 | 10:18 PM
