Rogue_Ant

If you do this, make sure your scope/probe can handle a 2-300 volt pulse - which is what happens on the negative side of the coil when firing...

This typically means at least a 50x probe, if not a 100x unit.

Dan Shea

Update: new ignition switch and new coil, still no spark.

I ran a test at the DME for the speed sensor, I got a very weak signal when cranking. The battery is dying so I will retry with the battery charged. But it made me question the DME side of the connector. I have continuity from #8 of the connector to #47 of the DME. But the weird one is I get continuity from both of the other wires to connector #48. Is that right or are the shorted? If I run the multimeter to between the two I have full continuity at the connection.

Dan Shea

Update tonight pt 2.

After charging the battery I got a good signal at the dme from the speed/ref sensor.

Still no spark from a plug connected to the primary wire off the coil.

With the light attached between the (-) end of the new coil and the lead off the ICM it would not light until I started cranking. Which leads me to believe I have a good signal coming out of the ICM when cranking.

Next step was to test the primary wire. I got 1k ohms of resistance between the two ends of the primary wire. That seemed really high for a 6in cable. So I pulled the primary off my pickup to test that.. It had ~200 ohms of resistance in a longer cable.

This made me think I had a bad connection with the primary wire. So, I ran a test wire out of the primary for the coil, to the tip of a spark plug which was grounded at the threads...

BINGO sparked like it should when I cranked.

I thought I had the problem solved, but now I'm looking into it and the wires should have ~3000 ohms of resistance.. what gives?

I'm out of ideas.

Dan Shea

Reviving this thread and my car hopefully.

So a little over two years now since the car ran, forgive me. I was sidetracked with an m3 and didn't have the drive to get this thing running, anyways..

The spark issue ended up being a brand new faulty ignition control module.

After draining the gas tank, new fuel filter, pump, and new injectors (3/4 were stuck open) Im having fuel pressure problems.

It wont building pressure when cranking.
With the ignition on and dme relay jumpered I get 49-50psi at the rail. It will hold and pass the leak down test IF I do not plug the dme relay back in.

As soon as I plug the dme relay I can hear something open and I lose all pressure at the rail. I can see fuel leaking into cylinder #4.

Prior to noticing that I was able to get the car to start for 3-5 seconds with one injector disconnected. It ran like crap and was more like an old car dieseling instead of running.

So do I have a broken wire in the injector harness? Is there a test for that? What else should I check?

Thanks much!

odonnell

You can pull back the rubber boots on the injector connectors. One pin of each injector should get +12v when the key is in the run position, the other pins are grounded by the DME when they are supposed to be pulsed.

The stock wiring has #3 and #4 wired together if I remember right, since it's a batch fire car. If it isn't #3 and #4, it's #1 and #4. Bottom line, one of your other cylinders will have fuel in it if the wiring going to the rail is at fault. If it's truly just that one injector and your other cylinders are dry, the injector itself might be bad.

Dan Shea

Ok I think I'm confused, or something is deffinately wrong with my injector harness. I'll check voltages at each pin this weekend, but help me conceptually here..

If the injector harness should be hot (12v) on one pin, and the other pin not hot/grounded when the computer says fire, shouldn't my Noid lights only light when they've got 12v and Ground (the fire signal)? Right now they light up as soon as I turn the key on and blink when cranking.

JacRyann

Are you connecting your test-light only to the injector connector?

odonnell

If the noid light is on, the injector is open. So if there's fuel pressure in the rail it's going to all be let out. Are all the injectors like that or just #4? It's definitely a wiring problem or a bad injector driver in the DME (this is a possibility if #3 is doing the same thing as #4)

Dan Shea

Yes the noid light is in the injector connector on the harness/rail.

All four injectors are like this, with it solid on (open) with the key on and the DME relay installed. When cranking they flash/flicker with the rpm.

I'm leaning towards a broken wire/short in the harness only because I had the ECU 'repaired' by ECU doctors back when I first was working on the car. Granted it's been 2 years, but it's been sitting in a garage the whole time out of the elements.

I feel like I saw a thread where the O2 sensor can ground out and cause faults with the DME Relay, but I haven't been able to refind it or get more clarification on how it occurs.

Dan Shea

Monday morning update, confirmed all of the injectors are seeing 12.5v on one side and .3 volts on the other with the key on and no injectors connected. It appears the one side is grounded somehow.

Do they share a common ground wire that I could have broken doing the o2 sensor? Any good places to check?

Thanks

odonnell

There are 2 "ground" wires. I put quotes because they don't go directly to a ground point - they actually go to the DME (pin 15 grounds 1 & 2, pin 14 grounds 3 & 4). When it's the correct time to fire, the DME sinks those pins to a ground at the right timing and the right amount of time.

Can you confirm that the ground pin on each injector only gets grounded during key-on? If so, the DME would be the first thing I would look at. A lot of people on here have had hit and miss experiences with DME rebuilders. In fact just 2 months ago I got one to test and it would only run the car for 4 seconds before dying (other DMEs ran it perfectly fine). You should ask to borrow a known good DME from a local to test in your car.

If they are a ground at all times (key off position) then it's probably a wiring issue.

Dan Shea

Update 2.0 following test pt 23 in garage shop manual I checked continuity between each injector term 2 to the corresponding pin on the ballast resistor in the engine bay. 1,2,4 had continuity, 3 was infinite (open). The manual doesn't go any further with details of what is within spec or what to do after testing, so I'll check the connection at 3 and chase wiring diagrams from there.

Sorry for all the details, hopefully they help someone else further down the road.

Dan Shea

Ignition off I get 7k ohms pin 2 to ground on all four injector connectors. Which to me sounds like it's grounding between the resistor and the dme?

Dan Shea

PS I don't think it's 14 and 15 at the dme, the s2 has a larger dme connector (50 pins iirc). Been searching online and think it's pins 24 and 17 on the s2.

Dan Shea

Update: Ended up being a bad ECU. Per the shop the circuit board had experienced a short and had to be replaced.

So, after all of this, and chasing my tail for 2 years. I finally got the car to start. Only to run into more problems.

First, it had really bad lifter/valve noise at startup. After letting it warm up it started to disappear and now is completely gone (phew).

Now, when the car is cold it will fire up after 2/3 rotations with the starter, usually it stalls after the first ignition. Second attempt, fires and idles nice and smooth until the engine temps hit ~180*. That's when it starts hunting and sounding like it has a miss every 4/5 rpm. If I blip the throttle it would stumble and rpms would fall to ~4/500 before it would struggle and correct itself. I believe I've corrected this issue with a new O2 sensor, the previous one was a splice connector with too much extra wire which melted/shorted to the exhaust. Now the car isn't fighting to hold an idle, but I still have a hot start issue...

Once the car is at temperature, if I turn it off, it will not start again until it is cooled off for about an hour. Starter spins, I have ~42Psi rail pressure (can't see it when I'm trying to start the car), and I have spark verified with tester. It will just crank/crank/crank with the occasional 2/3 fires but not enough to get the car started/running.

Clark's would point me to a faulty FPR, Fuel return valve, or the DME relay. All three of which are brand new and were replaced during my initial no-start fix. I also checked the Ohms on the DME temp sender and that checked within spec.

Is there any other random sources of a hot no-start issue that I can check? Would a vacuum leak cause a no start? I've replaced just about every sensor in this car and my patience and budget are running low haha.