Annual Failure to Thrive Problem

[dandydog]

Guys -
My '88 325ic has gone on its annual hunger strike, refusing repeated attempts to coax it into starting. Yeah, we've done this before: The first time turned out to be a cracked distributor cap; the next year it was a failed FPR. Geez Tech has been instrumental in locating the previous problems, and I'm hoping he'll pitch in again.
The fuel pressure is right where it oughta be (~40 psi), the plugs are new and the spark is good (I pulled #2 and left the plug on the valve cover); the position sensor tests out at 507Ω.
Immediately before the problem developed I'd replaced both the fuel pump and the position sensor for cause; both new units bench-tested fine and are installed correctly.
Anybody got any ideas? (Please don't tell me it's probably the CPU, because I don't have a spare. Besides, everybody always blames the CPU, and that's never it.)
Thanks for your help -
Neil

[Ray]

check the connections in the multi-plug. The signals to fire the injectors flow through there, (and maybe the crank position sensor too). Anyhow, I mean the one on the drivers side, more or less under the throttle plate.

[Ray]

C191 multiplug info

[Ray]

C191 multiplug info

[dandydog]

Ray -
Yeah, I know that puppy - I'll take a look. (And thanks for the url: I'll print it out and save it in my Bentley.)
Neil

[dandydog]

. . . because it isn't fuel-related (it doesn't even cough on starter fluid, the plugs are wet, and the C191 connector is intact and uncorroded), and I've still got good spark. So: if i've got fuel and spark, then it's gotta be a question of WHEN I'm getting spark or fuel, right?
Aside from the CPU, is there any other possible culprit?
Neil

[dandydog]

. . . Geez Tech have provided valuable help during my previous problems: It's just that GT's monicker is easier to remember. (Sorry, Jim.)
Neil

[Geez Tech]

...if they are wet then that means the injectors have been firing and you have confirmed you have spark.
How about the basics, valve adjustment good? Timing belt intact?
If I remember correctly your are near Denver? If so you may want to switch to a hotter spark plug considering the temperatures you drop to and the altitude you are at.
If that doesn't help then maybe ohm out the engine temperature switch for the DME that is on the thermostat housing, it is either white or blue. I think they are around 2000 ohms when cold.
Do I have to mention NO Platinums???? :)

[dandydog]

Thanks for signing in on this, Geez Tech.
The plugs are new already (about the second thing I did). By my reasoning, if the timing belt had broken, I wouldn't be getting any spark; and I've switched the engine temp sensor (it's blue) out already. (I've learned a lot from our previous consultations. Thanks.)
What may be relevant here is that, when the car died originally, it did so because the wire to the position sensor had broken. I jury-rigged the thing (with a couple of alligator clips and a carpenter's shim [to separate the clips]) in order to get home; that effort was successful, but the car wouldn't start again after that. It's possible that the shim wasn't entirely effective in preventing the clips from shorting out against each other (talk about your penny-wise and pound-foolish solutions.)
I know the sensor operates on high voltages: If there was a short, what would have gotten screwed up?
Thanks again -
Neil

[Geez Tech]

So you have replaced the jerry rigged sensor?
I'm not sure what would happen if the sensor shorted, I would think the CEL light would have come on at the least. That sensor is what helps the DME create the spark and timing, so it sounds like it is working, at least the spark part of it.
Have you tried to clean the plugs?
Is it a nice blue (strong) spark or is it orange (weak)?
For grins have you re-checked the cap and rotor?
Although not too common the coils can go bad over time.

[dandydog]

GT -
Yeah, I got a new (used) position sensor from e-Bay, tested and installed it; I changed the plugs (new, period-correct Bosch), and we're getting a good, strong spark. I've been meaning to pull the distributor cap, and I'll get to that today.
Is there some way I can get a LOOK at the timing? I'm really old-school, so I've still got a perfectly good timing light: If I hook it up to the #1 wire, is there anything to point it at? (Just to get some idea about whether it's the timing that's the problem.)
Thanks again for attending this annual ritual.
Neil

[Geez Tech]

I have never checked myself and I'm sure the emission label (Sorry, no E30's in the shop now)probably doesn't have a timing spec on it.
You could try to use the TDC mark on the balancer and the TDC mark on the lower timing cover to see if it is within reason, these are the ones you would use when doing a timing belt.
Have you put a noid light on a injector plug to see if it pulsates?
What were the "exact" events leading up to the no start condition?

[dandydog]

. . . because it got really cold again (remember, we're at 8500') and I got busy with some other stuff.
But you and I are on the same page, GT: I've got a little post-it note on my laptop, to be used as soon as it warms up a little, that says, "fuel: noid light; electric: timing light." I'll try 'em both soon.
As for the history: About a month ago, the position sensor failed (a half-hour's worth of diagnostic checks revealed a bad resistance reading on the used unit that I'd been using), and I replaced it, temporarily, with the original unit - one that still worked but had been removed because the insulation on the lead wires was cracked. 'Temporarily' went on for quite a while (because of the weather), and the car started to exhibit an occasional no-start condition which could be cured immediately by opening the hood and jiggling the position-sensor lead wire. I lived with this anomaly longer'n I should have, until, one afternoon, the jiggling resulted in the wire coming apart completely. I jury-rigged it as I described earlier to get it home, and I was feeling pretty satisfied with the job I'd done, until I couldn't get it running again, no matter how much I fooled with the alligator clips and the shim I'd used as a dielectric.
At that point, I took a little detour into why-don't-we-throw-some-parts-at-the-problem, replacing the fuel pump for no good reason. (However, I did, effectively, pick up a spare pump on e-Bay for $15, and I'm now back to let's-figure-out-what's-wrong.)
I'll do something more in the next couple of days -
Neil

[Geez Tech]

"As for the history: About a month ago, the position sensor failed (a half-hour's worth of diagnostic checks revealed a bad resistance reading on the used unit that I'd been using), and I replaced it, temporarily, with the original unit - one that still worked but had been removed because the insulation on the lead wires was cracked. 'Temporarily' went on for quite a while (because of the weather), and the car started to exhibit an occasional no-start condition which could be cured immediately by opening the hood and jiggling the position-sensor lead wire. I lived with this anomaly longer'n I should have, until, one afternoon, the jiggling resulted in the wire coming apart completely. I jury-rigged it as I described earlier to get it home, and I was feeling pretty satisfied with the job I'd done, until I couldn't get it running again, no matter how much I fooled with the alligator clips and the shim I'd used as a dielectric."

So have you replaced the sensor? If so was it new or used? if "new" were was it bought at?

Are we talking about the crank position sensor down by the harmonic balancer or the sensor on the spark plug wire?

Any chance during the "jerry rigging" and repairs you may have swapped the two connectors?


"At that point, I took a little detour into why-don't-we-throw-some-parts-at-the-problem, replacing the fuel pump for no good reason."
Again, new or used and were was it bought at? Have you put a fuel pressure gauge on to verify fuel pressure?

[dandydog]

. . . to what you've been telling me during our previous cooperative efforts: Both parts were bought used on e-Bay, and were bench-tested before installation (the crank position sensor's resistance is 547ʊ; and the fuel pump whirs happily when jumped to the battery) and re-tested in place (I've got a pressure gauge hooked into the fuel system, and it's showing right around 40 psi at the fuel rail; as for the position sensor: there's a good fat spark from any disconnected plug.) And no chance that I swapped the position sensor for the #1 wire at the connectors: We never disconnected the #1 wire.)
It's GOTTA be a timing thing. (I don't think it's the injectors because I couldn't get it to cough with starter fluid.) It's warming up outside, and I'll try using the timing light later today. (I'll also inspect the distributor cap and rotor, just to be sure.)
Thanks, GT -
Neil

[Geez Tech]

....If you have a good spark and lets say it is sparking well at the plug then you should get some sort of "cough" out the intake or exhaust even if the timing were way off.
Where are you spraying the starter fluid?
Maybe try spraying it with the fuel pump fuse removed.

Just be careful here, you are dealing with volatile starting fluid and possibly raw fuel, I dont want to hear about you on the news, LOL. Okay? :)

Thanks for "listening", sometimes I just like to go back and refresh things.

Does this have a Pringle in it?

[dandydog]

[dandydog]

. . . as good ol' Lonesome George used to say.
I don't know whether to laugh or cry: I'm really happy that I've finally found the problem (a cracked distributor cap), but I can't believe that I've had the same part fail on me twice, AND IT STILL TOOK ME THREE WEEKS TO DIAGNOSE THE PROBLEM!!!???
I'll pick up a new cap this morning and sign out after I'm certain that she's running again, but it's not too early the say Thank you, buddy! to Geez Tech. (" . . . and take another look at the distributor cap and rotor, just for laughs," I think is what you said.) Thank you for your good advice, your mentoring in the fine art of disciplined auto repair, and for your virtual companionship- it really helps, GT.
Neil

[dandydog]

. . . I really thought I'd identified the problem, but replacing the distributor cap did nothing to change the no-start condition. So tomorrow I'm gonna:
1) Pull all the plugs and make sure that they're all wet.
2) Hook all the plugs up and check that they're all sparking when the engine is cranked.
3) Reinstall the plugs and wires, then test a few of the injectors (odd- and even-numbered) with a homemade noid light (duplicates (1), but I'm running out of ideas.)
4) Pull the fuel pump relay and try to start the engine with starter fluid (carefully, a la Geez Tech.)
5) Check the (approximate) timing with a timing light and some sort of reference point while the engine is starter-cranked (I'll make this up as I go along, but I've got to get some idea if this is a timing issue [i.e., CPU]).
If anybody can think of any other tests, I'm certainly open to suggestions.
(You still with me, GT?)
Neil

[GeezTech]

Yep, still here.
If the plugs are wet they wont fire well so try to clean them. You can use some brake spray and compressed air, wear safety goggles so you dont get anything in your eyes.
Distributor caps usually dont crack, is it a OEM piece or aftermarket, like Advanced Auto? Dont over tighten it and tighten it evenly, make sure nothing is on the edge where the cap sits that may be putting an extra load on it in one spot.
I wouyldn't worry too much about the injectors right now as it should fire up on the starter fluid. Get it to fire on that first then go from there with testing.
Have you checked the air flow meter flap for being stuck open?