87 Motronic no start

Jesse16 · Jesse16's Garage

So here's where I'm at: Car will start and run briefly on starting fluid. Think that mean my speed and ref. sensors are OK. I've confirmed the fuel pump is putting out pressure at the check port. (no gage check, just confirmed its coming with pressure). I have spark obviously.
I'm checking pin 14 and 15 on the ecm plug looking for an output telling me its trying to operate the injectors and I can't detect anything. I also cannot "feel" anything at the injectors when cranking (difficult to feel). 240-11 in the Bentley talks about seeing battery voltage at each injector plug with ignition on, I can't seem to measure anything (how to check??). Everything checks good at the DME relay. I don't have an LED injector tester or digital pulse meter to check for pulsed voltage. The injectors were all rebuilt/cleaned 12 months ago during engine rebuild. Anything else that would cause my injectors to not fire other than a bad ECM ?

rusnak · 01-29-2012, 11:07 AM

Make sure the battery is fully charged, and that your grounds are clean. What is the voltage at the icv connector (easiest to remove the spring clip).

Flat6pac · 01-29-2012, 12:17 PM

Make sure all the ground wires are connected on the #1 intake runner and tight.
Bruce

Jesse16 · Jesse16's Garage

Idle Control Valve ? What would that do? The injectors aren't shooting gas.
I will do the diagnostic, no problem.

rsscotty · 01-29-2012, 01:34 PM

Did you just do an engine install or is this a new occurrence after it has been running fine?

Jesse16 · Jesse16's Garage

Also, (since I have someones attention), do you know what exactly is meant in the Bentley section 240-15, testing the ECM inputs/outputs. For Pins 14 and 15 which are the ecm outputs for Injection Time Signal, says the signal should be "ground pulse when engine running". Since engine won't run, I go back to previous page where it says for the same pins. With ignition on, fuel injectors should "click" when terminal 14 or 15 is grounded. That test is getting "no" discernible click. Tells me that the ecm normally sends power when running and then drop to ground causing the injector solenoid to open.

Jesse16 · Jesse16's Garage

I had pulled the engine to replace the clutch, didn't do anything else but of course lots of stuff got moved and touched. So far, all diagnostics for resistance, grounds, power, etc. have checked ok. The only place I'm stumbling is between the ecm and fuel injectors. As i said, the engine will run with starting fluid and I "seem" to have plenty of gas and pressure in the injection rails.
I tried to check the reference sensor while cranking and I don't think I quite know how to do that. What should I see at my little cheapie meter ? Because it does start with the start fluid and I have spark, not sure its even worth suspecting. It does Ohm check fine.

Jesse16 · Jesse16's Garage

How do you check for 12 volts at the injectors ? Check at bottom of 240-11. Says there should be battery voltage at the red/white wire of each injector with the ignition on. I'm not seeing any 12 volts any way I try it.

rsscotty · 01-29-2012, 01:50 PM

Something to check....

There is a multi pin plug on top of the rear shock tower cross member ( left side behind #3 cylinder) that is for the injectors. It is easy to forget to plug this in on a re-install.

Quicksilver · 01-29-2012, 02:32 PM

Quote:

Originally Posted by rsscotty

Something to check....

There is a multi pin plug on top of the rear shock tower cross member ( left side behind #3 cylinder) that is for the injectors. It is easy to forget to plug this in on a re-install.

On my car that plug is loose enough that vibration can make it flop around and makes the engine buck. I ended up putting a zip tie around it for the last 50k miles. Easy one to miss when putting the car back together.

Jesse16 · Jesse16's Garage

Got all 3 plugged in. I actually ohm'd all 3 from the ecm plug and they seem to read correctly. You can disassemble the big connector that plugs into the ecm and touch the back side of the connectors with your meter.

Jesse16 · Jesse16's Garage

Took out my ecm to look and it was repaired last back in 06, can't say by who. Has a bunch of marking on the box. I'll give S. Wong a call tomorrow and ask him if he believes I'm out of options and should send the box. Good excuse to have him finally put in his Chip. That'll be my reward for a week of testing and trouble shooting.

rusnak · 01-29-2012, 03:15 PM

You have to check the injectors connection with the engine cranking. Not likely all 6 are bad. Pita though, which is why I check for 12v at the icv. So it's either the dme (I believe sw detailed a spot on the board that controls fuel) or the power is too low to open the injectors.

johnman001 · johnman001's Garage

Are you sure you got the two flywheel sensors connected correctly? Plug everything back together and swap the two flywheel sensor plugs. I have done that countless times.

She may fire right up.

rusnak · 01-29-2012, 03:27 PM

I think the dme pulses ground. Maybe you can ground the voltmeter, and check for 12v at one of the injector plugs that way.

johnman001 · johnman001's Garage

The best way to check for injector pulses is with a noid light available at your friendly local car parts store (FLAPS). Check to see that the noid light flashes while cranking.

Jesse16 · Jesse16's Garage

Regarding sensors, they are connected correctly. Actually color paint coded from previous shop at some point. Real easy to not get them wrong. Bentley says you check for 12 volts at injectors with ignition on, no need to crank, unless thats wrong. Battery still has 12 volts every where else that I check. All dme relay checks seem to work great and my little switch jumper to make the fuel pump run works fine. I'll check on a "noid" light.
I'll go back to fact that it does run when I shoot in the starting fluid.
I was not able to see any 12v activity at the plug when my assistant ran the starter.
I did try to see the reference sensor pulse at the ecm harness pins 25 and 26 but not sure how to check. Says should see a +12 voltage signal on 26, with engine cranking. I couldn't see it.
Will do some of the other checks tomorrow. Thanks to all for the suggestions.,

rusnak · 01-29-2012, 05:58 PM

Since there is spark, and you say the fuel pressure is fine, then no need to suspect the sensors. I'd focus on the actual voltage at the injectors, and if there is a ground pulse. I think the noid light is a great idea. Again, you must check the voltage of the battery. You can have enough volts to crank the motor but not enough to open the injectors.

rsscotty · 01-29-2012, 06:00 PM

In post #9.... I asked about your injector wiring, but I was not clear on your reply. You said you had all 3 plugged in. What I was asking was if you had the black plug connected by the upper left rear shock mount.

Attached is a picture of the injector wiring harness. The black plug on the lower left of the picture plugs in by the shock mount.

Jesse16 · Jesse16's Garage

Think I plugged in that one ?? Hope I wasn't that in-coherent when lifting the engine up. Will double check when I can get my hands dirty. (I actually hope it got missed, save me a bunch of money.)