Another crank-no-start thread...different I hope

[SoCalSTI04]

I'm stumped and need the help of the collective wisdom here. I've looked over many, many threads on the topic so let me tell you what I've done so far. A little bit about the car - it's an E21 with a swapped in M20B25 from a later E30. Car used to belong to a friend of mine, it ran great, he sold it, still ran great then the last owner parked it under a cover for ~5 years. I managed to buy it back and didn't expect it to be so damn stubborn to get running again. Here are the steps I've gone through:
- drained fuel, replaced fuel filter
- Thinking it might be fuel pump relay, I wired up a separate relay so I can control when it runs. Still wired that way, but can put it back now that I know it'll squirt while cranking (not in key position "on" necessarily)
- Checked fuel flow which was a little weak...replaced fuel pump
- Checked for spark at the coil, there wasn't any so checked continuity between ECU and main relay, found that the fuel pump and main relay got swapped. In the meantime I kept hearing "crank position sensor" so replaced it then found that the new one reads 800 Ohms and the old one 500ish...went back to the old CPS but verified I did have spark after the relay swap so CPS is sensing the crank, at least somewhat.
- Replaced fuel injectors (the old ones were NASTY!) and fuel pressure regulator (Bosch injectors, another reputable brand pressure regulator, can't remember off the top of my head).
- Still didn't start, so I went back in and double checked that they don't squirt when key on pump running (since I have the relay bypassed the rail is pressurized) and that they DO squirt when turning over.
- Found two vacuum ports open on the manifold (near the throttle body and capped them. I don't know what they're there for, so LMK if this is important.
- Checked that the IAC is buzzing, took it off and cleaned it. Manually opened it up and it clicks shut when you then plug it in.
- Checked spark at a plug (had previously only checked at the coil)
- Plugged in the spare ECU/DME that came with the car, same behavior

A few more clues that I THINK aren't important but y'all know better than I do:
- Since I got spark, the starter kind of sounds like it's stalling out after a few seconds of cranking, then it starts cranking again. I can try to post a video if this is important. Maybe this says base timing is way off??
- I found the connector for the oil pressure sensor is broken (single plug on passenger side of block).
- I found that the oil level sensor plug (driver side of block near front) is a bit chewed up and doesn't click in place. I think it's making electrical connection. I've got aftermarket gauges so likely won't read out either way, but maybe it's important to start the car (seriously doubt it).

I'm getting weary from all this and would sure appreciate any help I can get. I think I've been through every YouTube video and forum checklist imaginable but sure hope I'm missing something and and someone out there knows what to check next.

[TobyB]

the starter kind of sounds like it's stalling out after a few seconds of cranking, then it starts cranking again.

Is there any chance the plug wires got swapped around? It's hard to mess up the base timing, but the thing still has a distributor and wires... oh.

How's the distributor cap look? Have you checked to make sure you're getting spark on all 6 plugs? That the rotor's not loose, damaged or burnt?

things that have caught me out,
t

[SoCalSTI04]

Hi TobyB I'll check the rotor and so far I've only checked 2 plugs and both are sparking. I will check the rest. The plug wires go into a plastic holder that keeps them in order and the lengths look right. I think it's highly unlikely that they're swapped, but I can chase them (and/or replace them) one at a time. Believe it or not, I asked ChatGPT and one of the things it said was that after sitting for long periods the timing belt can get loose and skip a tooth....I will check that. When I pulled fuel relay, it stopped doing the starter stall thing and when I used starting fluid (maybe got a bit carried away) it backfired BADLY out the intake. Seems to imply timing (valve or spark) is way off, in my mind, would you agree? Thanks again for your time.

[reelizmpro]

Since I just went thru something similar, check the grounds. The engine ground from the frame to the oil pan on the driver side in particular. Mine broke a few days ago and it wouldn't restart. The starter was acting similar to a low voltage/weak battery situation.

[TobyB]

The timing belt won't get loose, but it could, I suppose, rust to a sprocket and rip teeth off.
It's not too hard to check cam timing, and that's a good thought-
because I agree, if it were in front of me, I'd be thinking something's happening out of sequence.

A timing light's not usually all that necessary on an E30, but it might help you
figure out when the spark's happening. You can also put it on the coil wire and make
sure you're getting regular sparks while cranking. There are several faults
(yep, grounds are one) that can cause erratic sparking- which'll totally pop, buck and stutter.

sorry I haven't got more than guesses, but it's hard to diagnose over the internet.

t

[SoCalSTI04]

Thank you TobyB and reelizmpro for your inputs, I got it running last night!! While digging into the cam cover to just double check cam phase, I checked the spark plug wires and realized that they were put back on there backwards! The firing order was ALL wrong, hence the nasty backfire when I added the starting fluid. Replaced the cap and rotor, put the plugs in the right order, and viola she runs! Hard to believe that the PO would have even touched it when the car came with a new cap and rotor and the old one was obviously old...hence I didn't look there first. Again, thanks for the help!

[reelizmpro]

I always forget the KISS (Keep it simple stupid) method. It would have saved me so much time and money over the years. We assume so much when troubleshooting engines that we often overlook the basics. Glad you got it figured out.

[82eye]

Thank you TobyB and reelizmpro for your inputs, I got it running last night!! While digging into the cam cover to just double check cam phase, I checked the spark plug wires and realized that they were put back on there backwards!

i have seen it happen before and even done it once myself.
he probably installed them while standing on the passenger side of the car. you have to stand directly in front for the diagram in the bentley to be correct. i made my own afterwards

[SoCalSTI04]

The cap and wires are both numbered (in my case anyway) so it was really easy to spot once I pulled it off. Hoping to make it roll on its own tonight for the first time in half a decade!

[82eye]

good catch.