84 SC no start after rebuild

[87m491]

Thanks for the step by step. Unfortunately probably the weekend before I can get back to it. CHT is new and I can try the other tests mentioned as well. Kostal connector for injectors is seated properly at firewall but as mentioned PO tore through lots of wiring when converting the car to track use so it is all suspect.
I'm very heartened by the engine catching with starting fluid. I feel we are really close. Someone mentioned that if one injector is shorted, none will fire. I disconnected 3-6 and tried to fire, nothing. I can try the same on the other side but likely unnecessary if I test each alone. It's a little tough to get test leads firmly on the mid and firewall cylinders.

Originally Posted by ischmitz

During cranking the GND signal coming from pin 14 and 15 is only about 1 - 2 milliseconds in duration. A NOID light (an LED in a fancy package) will flash very dimly but it's hard to see unless the environment is really dark.

You may want to get yourself a simple oscilloscope (less than 30$ on evil bay) to make it visible. A multimeter will not help here. If it's not present check the wiring.

Disconnect all injectors and ohm out the GRY/WHT and GRY/BRN wires on the injector connectors back to the ECU connector pin 14 and pin 15 respectively. That's all there is to it.

[mysocal911]

Without having a scope to analyze the injector signal complicates the troubleshooting process.
A simple test while using a node light, is to disconnect the temp sensor. This will enhance the brightness of the injector signal significantly.
This is done first with the injectors disconnected. If there's no improvement in brightness, there maybe a short in the injector wiring.
If the brightness improves, you can connect & test each injector one by one, while using the node light.

Hopefully, you've tested the resistance (~2.5 ohms) of all the injectors before installation?

[ant7]

Just to make sure that you have spark and valve timing correct, spray some easy start into the intake while someone turns the key, if the engine starts and runs, then you know its definitely fuel/injector related.
Its a simple test, and will eliminate a multitude of checks.
Ant.

[wazzz]

Ant, read post #14 on previous page. OP has already sprayed ether at air intake and successfully got an engine catching for a few turns. So we know at least he's getting spark, meaning sensors are OK. As for the valve timing, that can be checked later on when he gets fuel. Right now only fuel is missing. He's already tried two ECUs, among which his own known good ECU from his own car (he's helping on a pal's car if I remember). Injectors are newly cleaned and checked. So what's left, wiring between ECU and injectors, and possibly one or two injectors electrically out of specs that could make the ECU flatline. This has already been seen in previous threads. Can't find the old thread where I read this, but the car wouldn't start on six injectors and would start on five, then die again when reconnecting the sixth injector. I mentioned that on previous page.

[ant7]

Ahh, my bad, I did go through the previous page briefly, but obviously missed that, I'll search the old grey matter, and see if I can come up with something useful to add.
Ant.

Originally Posted by wazzz

Ant, read post #14 on previous page. OP has already sprayed ether at air intake and successfully got an engine catching for a few turns. So we know at least he's getting spark, meaning sensors are OK. As for the valve timing, that can be checked later on when he gets fuel. Right now only fuel is missing. He's already tried two ECUs, among which his own known good ECU from his own car (he's helping on a pal's car if I remember). Injectors are newly cleaned and checked. So what's left, wiring between ECU and injectors, and possibly one or two injectors electrically out of specs that could make the ECU flatline. This has already been seen in previous threads. Can't find the old thread where I read this, but the car wouldn't start on six injectors and would start on five, then die again when reconnecting the sixth injector. I mentioned that on previous page.

[ant7]

Ok, how about getting a test light, remove all six injector plugs from the injectors so no chance of any injector issue messing with the test, plug test light into one of the injector plugs, then turning the engine over to see if there is any pulse light, if still no light then we can at least rule out the injectors causing the issue...
Ant.

[87m491]

Yes, I've heard one fried injector will cause all not to fire. that's why I discoed one rail and tried but no fire. I'll try the other. Working in shifts with the owner as he's retired and I'm still 9-5.

Tested;
CPS x 2 working, new CHT, (known working ECU and DME relay) new fuel filter, now new fuel pump, ~34PSi fuel pressure at rail, 12v to each injector lead 4-6, will test the rest. , spark at plugs, momentarily fires on ether.
As of yesterday did have noid light pulsing on a few injector connectors though still no evidence of fuel when pulling #4. maddening

Some suggested checking AFM output, will do as well.

Have got loaner oscilloscope to check other items. Will continuity test injector leads back to ECU. will also try to confirm valve and spark timing though when catching with ether sounds very normal.

I know we hate open loops on these types of threads but will update as squawk list items checked off.
thx

Originally Posted by ant7

Ok, how about getting a test light, remove all six injector plugs from the injectors so no chance of any injector issue messing with the test, plug test light into one of the injector plugs, then turning the engine over to see if there is any pulse light, if still no light then we can at least rule out the injectors causing the issue...
Ant.

[ant7]

I am wondering if the 12v supply to the injectors is dropping under load, there will be a big difference in the current needed to open the injectors in comparison to being able to light up a noid light.
Just a thought.
Ant.

Originally Posted by 87m491

Yes, I've heard one fried injector will cause all not to fire. that's why I discoed one rail and tried but no fire. I'll try the other. Working in shifts with the owner as he's retired and I'm still 9-5.

Tested;
CPS x 2 working, new CHT, (known working ECU and DME relay) new fuel filter, now new fuel pump, ~34PSi fuel pressure at rail, 12v to each injector lead 4-6, will test the rest. , spark at plugs, momentarily fires on ether.
As of yesterday did have noid light pulsing on a few injector connectors though still no evidence of fuel when pulling #4. maddening

Some suggested checking AFM output, will do as well.

Have got loaner oscilloscope to check other items. Will continuity test injector leads back to ECU. will also try to confirm valve and spark timing though when catching with ether sounds very normal.

I know we hate open loops on these types of threads but will update as squawk list items checked off.
thx

[mysocal911]

Again, disconnect the temp sensor and you should get the MAXIMUM amount fuel - max injector pulse width results while cranking!
The test light should be very bright. The AFM functionality doesn't affect this test. Avoid wasting time with naive "guessing" tests.


Start with a one injector load (connected) at a time with the node light.

[ischmitz]

Just to clarify: disconnecting one bank of injectors at a time isn’t the same as disconnecting all injectors. All 6 injectors are driven off the single low-side driver. Pin 14 and pin 15 inside the DME are connected to each other.

If you have a flashing NOID light with one of the 6 injectors disconnected you can look at either side of the injector pin connector with an oscilloscope and verify constant +12V on one side and correct injector signal on the other while cranking.

[ant7]

Originally Posted by ischmitz

Just to clarify: disconnecting one bank of injectors at a time isn’t the same as disconnecting all injectors. All 6 injectors are driven off the single low-side driver. Pin 14 and pin 15 inside the DME are connected to each other.

If you have a flashing NOID light with one of the 6 injectors disconnected you can look at either side of the injector pin connector with an oscilloscope and verify constant +12V on one side and correct injector signal on the other while cranking.

[mysocal911]

Originally Posted by ant7

I am wondering if the 12v supply to the injectors is dropping under load, there will be a big difference in the current needed to open the injectors in comparison to being able to light up a noid light.
Just a thought.
Ant.

YES! That's why you start by ONLY connecting ONE injector to begin with using the noid light, and then add additional injectors.
You can also add a VOM to monitor the 12V injector supply voltage at another injector plug.

[ant7]

Originally Posted by mysocal911

YES! That's why you start by ONLY connecting ONE injector to begin with using the noid light, and then add additional injectors.
You can also add a VOM to monitor the 12V injector supply voltage at another injector plug.

[87m491]

Update. My buddy, the builder, said while checking timing yesterday, car fired up on 2 cylinders. He said 1 and 6. No idea how he could tell which ones.
I went at lunch time today. FP rate was 1.5 liters in 30 seconds. (Bentley spec is .875ltr)
I tested AFM resistance, linear response to moving flap. I could not measure any voltage change across the AFM so I thought we found the culprit.

When replacing AFM harness, the male end kept dislodging the keeper clip on the plug and I could not get it to properly seat. I flipped the keeper clip 180 and refitted the harness clip. To see if we could replicate 2 cyls running we cranked it over. After 2-3 seconds the damn thing fired up like it had never been apart! No smoke, no smells, no immediate leaks just pure flat 6 noises. Wish I had a concrete answer, but it seems great.
Thanks a ton for the ideas and check lists. A huge shout out to Sal Carceller knower of all things electrical 3.2 for lot of PM help.
Comp #'s below

[ant7]

Good news!
Ant.

[stubble88]

Damn. Dealing with the exact same thing on my 3.2/3.4
I hope it’s this same problem.

[87m491]

Originally Posted by ant7

Good news!
Ant.

Aaarrrgghh, so close. Got a leaker!

[ant7]

You win some, then always with these old cars, its something else!
Ant.

Originally Posted by 87m491

Aaarrrgghh, so close. Got a leaker!