Adamant1971

Ok so we recently put the engine back in after a complete rebuild. On the first start the engine ran for 2 or 3 seconds then died to what appeared to be a lack of fuel. We also witnessed a little puff of blue smoke come up from the MAF/CPS area, we do no know if this is related.

Ok now on to what I have checked so far:

1: The car is getting fuel, system pressurizes well and fuel can be heard returning to the tank.
2: We had spark initially, tested via a spark tester and by testing voltage at the coils. But as of today we have no power at the coils when cranking.
3: Both the EZK and LH relays have power on terminal 30 and both have continuity from pin 87 to the plugs at the computers.
4: When testing the power at the LH relay via terminal 30 I get 12 volts when using the firewall as a ground, but when I use the top terminal for the relay I do not get any voltage. (I want to go back and test this again to make sure)
5: I have swapped out relays and have also jumpered the LH relay with no change.
6: Tach does not move when cranking. (I can't remember if it did on the first start)
7: CPS is new and I get the same scope readings from pins 6 and 23 on the EZK harness as I do on my running 87. And we swapped it out with known good used one with no affect.
8: No power at injectors when key on or when cranking.
9: Good continuity on CPS wires, hall sensor wires and temp sensor wires.
8: I have tested both the EZK and LH in my 87 and it ran fine.
9: Most of the connectors have been replaced on the injector harness and on the front harness
10: Good power at the jump post.
11: 14 pin harness re-soldered.
12: On terminial 1 (speed from EZK 13) on the LH plug I get 12v when key on. On my 87 I only get 5.5v?
13: On terminal 13 (speed pulse to LH 1) on the EZK plug I get 12v. Again on my 87 I get 5.5v?
14: EZK terminal 35 has 12v, and terminal 29 has 12v with key on and good continuity to terminal 87 at the relay.
15: Both diagnosing terminals on the EZK, 1 and 7 have 12v
16: LH terminal 35 has 12v, and terminal 21 has 12v with key on,
17: LH Terminal 9 also has power and continuity. As does terminal 4
18: Hall sensor is new as is pretty much everything on the engine.
19: Inspected back of CE panel for any loose connectors or wire damage, all loooksok.

Update: Based on other similiar threads I think I should check the following next:
1: Maybe one injector wire is shorted?
2: Maybe the ignition monitoring relay is toasted or maybe the temp sensors?
Or is there a chance the factory alarm is to blame?

Any help or ideas would be greatly appreicated.

Mrmerlin

did you label all of the connectors? it would be a good idea to replace all of the connectors,
from your report you have wire smoked the Bosch.

EDIT #8 I missed that you tested the puters.

soontobered84

The things that stand out to me are:
No power at the coils
No power to any of the injectors
The computers work in the 87.

It sounds to me as if you have shorted a wire at the MAF (connector?)that is critical to both ignition and fueling. Now you just have to figure out which one.
You might pull the MAF connector and check that any terminals on the MAF are not bent over or whatnot

Adamant1971

Yes all labled , I was meticulous, had the whole loom layed out on cardboard etc.
On the injection harness the only connectors that were not replaced were the MAF plug, the head temp sensors and the main plugs at the computers, the rest were all replaced and the harness was checked for continuity prior to installing.

Will take another look at the MAF connector tonight. The wiring is pretty brittle, anything is possible. Is there a good thread for the testing of the MAF harness. I will search.

Adamant1971

Ok some more data:

MAF
-Terminal 1 on MAF harness has good continuity to terminal 8 on the LH harness
-Terminal 2 on MAF harness has good continuity to terminal 87 on the LH relay at the CE panel
-Terminal 3 on MAF harness has good continuity to terminal 6 on the LH harness
-Terminal 14 on MAF harness has good ground
-Terminal 5 on MAF harness has good continuity to terminal 7 on the LH harness
-Terminal 6 on the MAF harness is empty
MAF is a rebuilt unit from Roger. I will test it tomorrow in my 87 to make sure we didn't kill it.

INJECTORS
-Terminal 18 on the LH harness has good continuity to the injector wire 1, it has 1.5 ohms of resistance to the 2nd wire at the injector harness.
-Injector wire 1 has a good ground and wire 2 has 1.5 ohms of resistance
-I checked the resitance between wires 1 and 2 at the injectiors and I get 1.5 ohms again
So is this the short? Since the LH grounds the injectors to fire them I should not see any ground with the car off. Also assuming I should not see any continuity between wires 1 and 2, but I am.

Update: I could not get the MAF out of my 87 to swap in this one as mine is stuck. Heading out tomorrow for a week of skiing in Quebec so this will have to wait until I'm back on March 4th.

Adamant1971

Back from Vacation and back it this.

I swapped the MAF into my 87 and it ran fine. So the MAF and MAF wires all check out OK.

I jumped the LH relay (pins 30 & 87) so I could check for voltage at each injector. When jumped I have good voltage at the injectors (pin 1). But I get a voltage reading when either grounding to the chassis or to the second wire on the injector plugs. It's my understanding that the LH grounds the injectors and they then fire. So it looks like I have a grounding issue. This was done with the LH and EZK disconnected, and the Ignition Monitoring Relay connected. When I disconnect the monitoring relay I loose voltage at the injectors as expected. Now with the battery disconnected and the LH relay still jumped and the ignition monitoring relay connected I'm getting a solid ground from pin 2 on each injector to the chassis, when I disconnect the monitoring relay the ground continuity is gone.

I had a chat with the owner about how the car ran before it went into storage many years ago and he told me that it was intermittently loosing power, so it was likely going into limp mode. Now to further inspect and test the Ignition Monitoring Relay, unfortunately I do not have another unit to test against.

I double checked again and I have good continuity from pin 13 on LH harness to the injectors.

Any thoughts?

Adamant1971

dr bob

-- Make sure the injector ground wiring is clean and secure at the rear of the intake manifold in the V. It's quite possible this is loose or not connected, giving you the no-injection and the escaping smoke.

-- Unplug all the injectors and test again at the ignition protection relay socket, the injection relay socket, and the LH for short to ground in injector wiring. With those out there should be no path to ground on any injection wiring. The only "ground" in the injector loops is at the LH controller via the ignition protection relay contacts. This is the relay on the controller mounting frame, the one with the LED's and the connections from the exhaust system thermocouple probes.

Adamant1971

One of the first things I checked was the injector harness ground at the back of the V. It's tight and I get contuniuty from that ground to the chasis.

I did test the injectors again and the protection relay socket. I got good continuity to each bank of injectors.

I have everything back together again, re-pressurized the fuel system to check for leaks at the the FPR, cranked it over without fuel to check fro spark at each distributor and I have spark.

So I attempeted to start her, she sputtered a tiny bit then back to the feeling of no fuel. Is it possible I just don't have enough fuel in the tank? I put in about 8-10L. The FPR was abvioulsy bad, when removed fuel came out the vacumm port.

So to re-cap:
-I have no tach movement but CPS checked out fine with a scope
-No oil pressure reading
-I have spark and good voltage at the coils when cranking
-Fuel pump is new and running

Next, I'm going to hook up a node test light up to the injectors and crank her over to determine if they are getting the pulse to fire or not. And I will put for fuel in the tank.

Stay tuned

Adamant1971

No love with the injector node light, with LH relay installed or with the relay pins jumped. No light on the node, so the injectors are not opertating. And still no tach, so all signs point to the CPS, but that has already been gone over and the scope results I got from a new cps are the same that I'm getting from my running 87????

I took note of the ignition monitoring relay and I do not get any lights when ignition on or while cranking.

I need to make a better jumper wire and give this a go once more with the monitoring relay jumped.

Ken P

This stands out to me. It sounds like you checked this with the key on, but not cranking?
Can you put a scope on this as well? This should be a square wave and about 10v, to turn on the LH computer.
Without a proper signal here, the LH will not fire the injectors.
Test with the EZK plugged in and the LH upplugged. Terminal 17 and 1 to the oscilloscope, pin 1 is the signal pin.

This is test point 15 on page D 24-22.




Engine speed signal to LH, This should be about 10v.


Something else to check is if this is a manual car with Auto Trans kick down relay installed or,
If it is an auto car, is the correct relay installed in position 15. If the wrong relay is in there, it could affect this signal.

Ken
'89 928 GT

Adamant1971

Adamant1971

No big progress on this, since I have been noodling it. Sometimes the best thing to do is walk away and think.

Last night I did double check that I did not switch the TPS and CPS plugs, based on another no start thread. I did notice that I have both injector grounds grounded at the same bolt on the back of the V, so I will clean those contacts again and move one to the other bolt, just to rule out any ground issue. Then this weekend I plan on giving her a once over again, circuit by circuit (tests 2-15 in WSM).

If that fails I will pull the injector harness and dissect it to look for a fault before sending it to Roger for a rebuild.

Adamant1971

So today I decided to go back and inspect the grounds, CE panel etc. I moved the injector harness grounds from being on one bolt to each going to their own bolt on the throttle cable assembly. No change.

So then I decide just to run thru the test points again.

Test point 2 - Idle speed contact - D 24-11
Closed should be less then 10 ohmms - My reading 5 ohms
Open 1 degree should have continuity - My reading 1.56 k ohms (FAIL)
On the tps harness pin 1 has good continuity to pin 5 and pin 2 has good continuity to pin 2 at the LH

Test point 3 - Full Load Contact - D24-13
Throttle closed should have continuity - My reading 1.56 k ohms (FAIL)
@/3 open should be less than 10 ohms - My reading 1.9 ohms

Test point 4 - Engine Temp - D24-14
Temp 2 sensor should measure 4.4-6.8 k ohms at 0c - At about 10c my reading is 0.835 k ohms (FAIL)
The ground is good at the sensor.
I get good continuity from pins 13 and 17 at the LH to the temp sensor
I get 8 ohms accross the sensor, pins 1 and 2.

Test point 5 - Air Mass - D24-15
Battery voltage checks out at pins 2 and 4 at the MAF.
Hot wire restiance should be 3.6-4.1 ohms - My reading 1.56 k ohms (FAIL)
Hot wire signal should be 1.6v - My reading 1.8v
When blowing on the wire the voltage goes up

Test point 10 - Injection circuit - D24-19
Jumped relay and no change

Test point 12 - Power to LH - D24-20
13.1 v pins 17 and 4
Power through relay 13.1 v as well

Test point 13 - CPS - D28-11
Solid 3v wave while cranking

Test point 15 - Speed signal from EZK - D24-22
11.5 mv square wave with ignition off???
Only small chatter when cranking (FAIL)

So based on what I'm seeing the Temp 2 sensor, TPS and MAF have failed/fried. Although the MAF did work in in my 87 (only idle, to wintery to drive it). And the speed signal from the EZK to the LH is bad. I think my next step will be to pull the intake and remove the injection harness for further inspection.

Here is are pics of the scope results:


CPS to EZK


EZK to LH ignition off


EZK to LH cranking

Ken P

This sounds like the switch is functioning, You didn't have your fingers on the test leads did you? I can get my meter to show that type of resistance through my body.

This does sound off, this is a lower reading than you should have. Can you verify this with another meter? And the readings above.

Can you change the frequency to get a tighter waveform? When I tested my car and Barneys I was getting 12v + and able to see the reference signal as well.


I still think this is where the current issue is, if that signal is not a nice square wave during cranking.
If you could isolate the pin out of the CE panel W11, that would eliminate anything in the CE panel, the relay socket and the instrument panel. I think I remember someone telling me that the instrument panel (Tachometer?) could load down the signal and keep the LH from turning on.
This is what I would try to figure out 1st, if a retest of the CPS signal shows the reference mark and the signal closer to 12v.

I would then retest those Ohm reading and maybe try another meter.

Ken