No start suggestions (not typical) RESOLVED!

[ForcedFirebird]

Looking for suggestions. I have a small shop and have done several 2.7i conversions, turbo kits and even write chips for OBD1, but have never come across something like this (thinking it's electrical - maybe harness?)

uel relay not kicking.
No spark.

1984e with Motronic 1.3 and 885 top end - early 1.0 harness.

All +/- on DME checked, CPS checked, all relays checked, fusable link checked, pump checked out via pressure, filter is new, coil is good, grounds are solid.

The harness is used and had an issue at the AFM, but I used the old e harness to make it right, soldered heat shrunk and resistance tested, same as with the injector portion, also corrected with solder, heat shrink and resistance tested.

I made and adapter pigtail for the old square c101 to the new round c101 and mated all the corresponding wires together, all soldered, shrink and resistance tested (again, this is one of several of the same projects completed - 2.7i and m50 swaps).

Full aware of the orientation of the crank and cam position sensors, they are plugged in correctly.

It' acting like it isn't seeing the CPS (or if the CPS/cam reluctor were mixed up which aren't) but this thing has me stumped.

Guess the next thing is to test every connection at the ECU with the corresponding sensor or is there an easier way to check the harness?

EDIT: CPS space to hub is checked, damper checked out for correct position...

[jlevie]

Here you go...

For the engine to run the following conditions must be met:

Power on DME pins:
27 Start Input
18 Un-switched Power input
37 Power Input from Main Relay

Ground on DME pins 2, 14, 19, 24

Timing data from the CPS on DME pins 47 & 48 from a rotating engine

To have spark power must be present at the coil positive and ground pulses
from the DME's pin 1 must reach the coil negative. Power to the coil is
controlled by the ignition switch via C101. When checking for spark, use the
output lead from the coil to eliminate the distributor, rotor and plug wires.

To have injector firing power must be present at each injector and ground
pulses from the DME's pin 16 (Bank1) and pin 17 (Bank2) must reach the
respective injector bank. Note that the injectors are wired as two banks of
three. With cylinder 1,3,5 being bank 1 and 2,4,6 being bank 2. Power to the
injectors is controlled by the main relay. Injector firing is best checked
with a noid light.

The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30. The DME will ground pin 85 to turn on the
relay and power the pump(s) via pin 87. Of the above, only the fuel pump power
is fused. So if the there's power at pin 87, but not at the pump, check fuse
11.

The main relay and DME pin 18 receive power from the smaller of the to wires
that connect to the battery's positive terminal. That wire incorporates an
in-line fuse. When the DME is presented with a start signal, it grounds the
main relay pin 85 and furnishes power to the fuel pump relay, injectors, and
DME.

Troubleshooting:

Disconnect the battery and the DME cable. Then:

1) Disconnect the coil negative and check continuity from that connector to
DME pin 1. Also verify that from DME pin 1 to ground is an open circuit.

2) Check the resistance across DME 47 & 48, which should be 500-560 ohms. If
the CPS is dismounted, the resistance can be seen to change from about 500 to
540-560 ohms when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

3) Check for continuity from DME 36 to main relay 85 and from DME 3 to fuel
pump relay 85.

Reconnect the coil, remount the CPS (air gap should be 1mm), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

1) With the key off, verify that power is present at DME pin 18 and main relay
86 & 30.

2) With the key on, verify that power is present at DME pin 27 and pin
18. Power to pin 18 is from the main relay and there should be power to the
injectors and fuel pump relay.

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

4) Verify that power is present at the coil positive and at fuel pump relay
pin 30. Those get switched power from the ignition switch via C101.

The engine will start and run (if poorly) with only those connections to the
DME in place. The other signals from Cylinder ID, AFM, temp sensor, etc., are
necessary for proper operation. But they won't prevent the engine from firing.

IMPORTANT:

A power check means seeing a voltage within about a tenth of a volt of what
you measure across the battery terminals, which should be at least 12.6v on a
charged battery.

A continuity check means seeing less that 1 ohm of resistance.

An open circuit means seeing a resistance of at least 100k ohms.

A good quality auto-ranging digital multimeter will make these tests much
easier.

[ForcedFirebird]

Here you go...

For the engine to run the following conditions must be met:

Power on DME pins:
27 Start Input
18 Un-switched Power input
37 Power Input from Main Relay

Ground on DME pins 2, 14, 19, 24

Timing data from the CPS on DME pins 47 & 48 from a rotating engine

To have spark power must be present at the coil positive and ground pulses
from the DME's pin 1 must reach the coil negative. Power to the coil is
controlled by the ignition switch via C101. When checking for spark, use the
output lead from the coil to eliminate the distributor, rotor and plug wires.

To have injector firing power must be present at each injector and ground
pulses from the DME's pin 16 (Bank1) and pin 17 (Bank2) must reach the
respective injector bank. Note that the injectors are wired as two banks of
three. With cylinder 1,3,5 being bank 1 and 2,4,6 being bank 2. Power to the
injectors is controlled by the main relay. Injector firing is best checked
with a noid light.

The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30. The DME will ground pin 85 to turn on the
relay and power the pump(s) via pin 87. Of the above, only the fuel pump power
is fused. So if the there's power at pin 87, but not at the pump, check fuse
11.

The main relay and DME pin 18 receive power from the smaller of the to wires
that connect to the battery's positive terminal. That wire incorporates an
in-line fuse. When the DME is presented with a start signal, it grounds the
main relay pin 85 and furnishes power to the fuel pump relay, injectors, and
DME.

Troubleshooting:

Disconnect the battery and the DME cable. Then:

1) Disconnect the coil negative and check continuity from that connector to
DME pin 1. Also verify that from DME pin 1 to ground is an open circuit.

2) Check the resistance across DME 47 & 48, which should be 500-560 ohms. If
the CPS is dismounted, the resistance can be seen to change from about 500 to
540-560 ohms when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

3) Check for continuity from DME 36 to main relay 85 and from DME 3 to fuel
pump relay 85.

Reconnect the coil, remount the CPS (air gap should be 1mm), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

1) With the key off, verify that power is present at DME pin 18 and main relay
86 & 30.

2) With the key on, verify that power is present at DME pin 27 and pin
18. Power to pin 18 is from the main relay and there should be power to the
injectors and fuel pump relay.

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

4) Verify that power is present at the coil positive and at fuel pump relay
pin 30. Those get switched power from the ignition switch via C101.

The engine will start and run (if poorly) with only those connections to the
DME in place. The other signals from Cylinder ID, AFM, temp sensor, etc., are
necessary for proper operation. But they won't prevent the engine from firing.

IMPORTANT:

A power check means seeing a voltage within about a tenth of a volt of what
you measure across the battery terminals, which should be at least 12.6v on a
charged battery.

A continuity check means seeing less that 1 ohm of resistance.

An open circuit means seeing a resistance of at least 100k ohms.

A good quality auto-ranging digital multimeter will make these tests much
easier.

Thanks for the fast and accurate response, jlevie. So glad you were on when I came across this.

DME pin 3 > FP relay is open. You just saved me a few hours in swapping the harness for a bad wire.

Hat's off to you good sir!

Had all the basics covered, but was going crazy looking at the block diagrams for 2 different models :/

[ForcedFirebird]

Well jumped a wire through the passenger door for DME 3 > FP relay 85 - no spark- will continue through your diagnosis algorithm.

[ForcedFirebird]

Went through entire diagnostics you suggested using an LG digital multimeter, now that DME 3 > relay is jumped, still no spark.

Used 2 different DME's, one with a stock file on the chip, the other has a chip for the larger inj in my personal car just to see if DME was bad.

All relays pulled from my car (running) and moved to the subject, no start.

Adapter is as follows:

Square plug > c101 round

1 d+ > 1 d+
2 sta > 2 sta
3 blank
4 FT > 4 FT
5 blank
6 15s > 6 15s
7 EP > 13 EKP
8 50 > 18 50
9 blank
10 15u > 7 15u
11 blank
12 blank
13 blank
14 blank
15 dyn > 10 dyn
16 oil > 5 OELD
17 SI > 11 SI
18 blank
19 blank

Left open on the c101 is as follows (chassis side):

8 (DME control) white/green
14 (tach attached in glove box) black
15 (starter engine plug) blk/grn
16 (airbag)
20 (FTM?)

[ForcedFirebird]

It's got to be the harness. When moving my car back in the shop last night, the relays that were moved the the subject were no longer working. :(

Going to try another harness and see what happens.

[ForcedFirebird]

RESOLVED:

Changed the harness to a known good late harness, fired right up. Too bad there was several hours lost to not only repair the customer-provided harness, but to diagnose then change them out.

Note to self: Check over all parts a customer provides :(

[jlevie]

RESOLVED:

Changed the harness to a known good late harness, fired right up. Too bad there was several hours lost to not only repair the customer-provided harness, but to diagnose then change them out.

Note to self: Check over all parts a customer provides :(

Used harnesses are a real "roll of the dice". My Spec E30 is on it's 4th "known good" engine harness. The previous ones having to have been replaced for problems with the CPS signal. I'd get a new harness if the darn things weren't so expensive.

I'm going to take one of the harnesses and replace the coax that routes the CPS signal to the DME. My theory is that the insulation on that pair of shielded wires breaks down with time & heat and causes problems.

[ForcedFirebird]

I agree. We know GM systems very well and you will receive mis-fires upon warm up when the shields start to corrode. I have known a few to extend the ever elusive "paired" reluctor wires, but would never do it on my own since we all know that length adds resistance.

By the way, 540ohms at the ECU on the last harness.

I am just glad I got this stupid thing fired up, then now have the issue of the coolant port on the back of the head dripping, another 1st for me - specially since I put "The Right Stuff" on all the gaskets after they come back from the machine shop :(

Now going to unbolt the trans mounts and hope the motor can be tipped forward enough to get to the 2 10mm bolts while in the car.......

Fun never ends, does it?

Thanks for your advice. Seems you know your way around m20's pretty good :)

[jlevie]

I am just glad I got this stupid thing fired up, then now have the issue of the coolant port on the back of the head dripping, another 1st for me - specially since I put "The Right Stuff" on all the gaskets after they come back from the machine shop

Now going to unb:(olt the trans mounts and hope the motor can be tipped forward enough to get to the 2 10mm bolts while in the car.......

The last time I had to fix a leaking head nipple I lowered the subframe and engine a few inches.

[ForcedFirebird]

The last time I had to fix a leaking head nipple I lowered the subframe and engine a few inches.

Can get in there if you take the 2 hex nuts off the trans bushings and jack the rear of the trans up a bit, just did it.

I was the dummy that used the black silicone "Right Stuff" and never tightened the bolts after letting it skin lol. Fixed now.

Car idles perfect but dies with any throttle, much like a large vacuum leak, yet no leaks. Maybe uploaded the wrong file to the chip. Either way, car is back together finally, just have to connect the tach and econoguage to this 2nd harness.

Should show some pics of this car, very sweet.

[ForcedFirebird]

And the saga continues. New harness, no CTS or TPS pickup when plugged into an emulator, no coolant temp guage.

Clipped the end off the harness side of the round inj connector, had 2 open circuits. Soldered and shrunk the pigtail from a donor harness and now have continuity to the proper ECU pins, but still no guage. Checked for ground continuity through the temp sensor plugs and at TPS, all good.

Tested 1&3 on the TPS connector and we have 12v instead of 5v.

Only my luck to have 2 bad harnesses in a row?

[ForcedFirebird]

OK. Not the engine harnesses causing the problem. Took the harness out, cut the shrink and traced all the wires, everything looks good, all continuity checked out, no cross talk.

Took a known good harness from my car and just connected the B+, grounds and c101.

Still getting B+ at the TPS leads. What could cause this in the body harness?

[Sagaris]

Goodness! I hope I never have to get so deep into an electrical harness gremlin. I had one with my wifes Toyota. After about 6 hours of diagnostic time I had determined that the voltage regulator on the alternator had failed and every wire and component in the car had been seeing too much voltage for the few months prior to that. It wasn't worth attempting to fix and I had to wholesale it to a dealership for way too cheap :\

So you are getting 12V at the TPS. Which pins?

[ForcedFirebird]

The two outside pis that should read ~5v with key on.

It's an 85e with an is swap. See above for the harness adapter wiring.