First of all, thanks for the suggestions I've received thus far. Unfortunately, I'm still stuck.

Synopsis: '88 240 won't start. If left alone for 10 minutes, it'll start for just a second (and sound perfectly fine) but then immediately die.

Things I've looked at so far:

- replaced the 25 amp fuse *and* fuse holder
- replaced all the fuses with new ones, cleaned all the contacts with a wire brush attachment on my dremel tool, and dabbed contacts with dielectric grease
- tested main relay *and* tried brand new one (both relays are on when cranking)
- jumped fuel pump fuses -- main pump sounds fine
- tried starting with AMM disconnected
- cranking produces slight gas smell, including stronger smell from tailpipe
- all tests at ECU from Bentley manual OK
- checked for spark at plug #1 -- looks fine
- resistances at coil OK

I haven't looked at the ignition system in detail, so that's next. Any suggestions are most welcome.

Thanks,

-Lujo
'88 240 in Princeton, NJ

Hi all,

A few months back I posted a couple of questions while trying to solve a no-start. It's since been solved, so I thought I'd post the solution, since I haven't seen it mentioned and it's a trivial thing to try. The car didn't seem to be getting fuel, though occasionally it would sputter for a few seconds before going back to sleep. Turns out there was a problem with the electrical connectors on the main fuel pump. They looked perfectly OK, but cleaning them solved the problem instantly.

Cheers,

-Lujo
'88 240DL
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Lujo Bauer ('88 240 in Princeton, NJ)

Lujo,

You are not alone with your no-start difficulty.

My '89 740 Turbo crapped out much the same way.....ran fine for about half an hour then suddenly quit and won't restart.

It tries to start after I squirt something combustible, like carb cleaner, into the intake.

Seems to get no fuel otherwise.

Some have sugested the Hall Effect sensor, the RPM sensor (don't have this on the turbo engine) or the radio suppression relay (which is a fuel system relay)
--
1989 740Ti 1986 240DL 1984 244GL

My first thought was the same as Don Foster's suggestion to check the fuel pressure regulator. Sounds (smells) like it is flooded.

You mention having done the ECU checks. Did you get a good resistance reading on the engine coolant temperature sensor?
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Art Benstein near Baltimore

Yeah, the resistance on the coolant temp sensor was fine. Could a bad sensor cause the car not to start?

What I worry about with the ECU checks is that the problem looks like it might be a weak electrical connection, so even if everything checks out fine who knows what it's like with more current flowing.

Any other thoughts?

-Lujo

Just found and read your first thread on this describing the "sudden onset" nature of the malady. Strikes me now like back to ignition.

Do you have a tach or a timing light or some other way of making sure you still have hall-effect output when it quits? I can think of a couple common reasons your ignition might fail soon after starting, beginning with the hall sensor and pausing at the ICU plug and heading toward the fuse panel and ignition switch.
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Art Benstein near Baltimore

I just checked again for spark (for details see my reply to Don at http://www.brickboard.com/RWD/index.htm?id=593401) and it seems like there's good spark at all four cylinders, so I'm thinking fuel delivery again. I have a timing light somewhere, I think, but given that there's spark at all four plug wires, that question becomes academic, no?
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Lujo Bauer ('88 240 in Princeton, NJ)

Well, actually this whole process of attempting to help someone fix their own car by question and answer is academic. I'd already read your reply to Don when I posted the suggestion your spark may be there when you crank and test, but fail soon thereafter.

Simple question, really, about the tach and timing light, but I guessed fuel delivery first, and you know how tests in academia are usually better answered with your first guess. Good luck, Lujo.
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Art Benstein near Baltimore

I'm sorry if didn't explain myself well in my previous post. I didn't mean to suggest that I was second-guessing your suggestions -- I was just trying to fully understand what you thought the problem might be. I wanted to be sure that you had seen my post about spark while cranking because I didn't know whether you were suggesting that it might be an ignition problem despite seemingly good spark. In any case, I find your suggestions instructive regardless of whether or not they immediately pinpoint the problem, and I'm grateful you took the time to post them.
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Lujo Bauer ('88 240 in Princeton, NJ)

"I'm sorry if didn't explain myself well in my previous post."

No, I owe you an apology, Lujo. I found your response thought provoking and amusing, not personally challenging. The "its academic" led me to a generalization about all our technical help posts, meaning for us, who are not under the hood, but in the armchair, it really is academic.

No one can better solve a real problem than he who has it.

Anyway, maybe I had better collect some graphical emoticons (smile) so my academic digressions don't get seen as criticism. Sorry.

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Art Benstein near Baltimore

"Could a bad sensor cause the car not to start? "

Could help if it already flooded the motor. But I thought it did start when aired out, but wouldn't keep running. That, and finding fuel in the tailpipe is why I thought FPR.

Also I misread your post thinking you had eliminated ignition as the trouble instead of asking if ignition could be the trouble after verifying spark at #1. It implied there are some previous threads; perhaps I should go looking for them to find out what brought on the condition.

As far as weak electrical connections, the one I asked about would be well checked by the resistance measurement. But, like any static measurement, the ohmmeter will not show up mechanical intermittents that don't happen to be having trouble at the time. Happened to me, but in LH2.0 the symptom was intermittent stalling and stinky poor idle.

Smell of gas..... hmmm.....

Are the plugs wet or dry after crank-crank-crank?

Could be a bad fuel pressure regulator.....
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Don Foster (near Cape Cod, MA)

Plugs look dry (is a wet plug actually supposed to be damp with gas, btw?). The FPR looks OK on the outside (i.e., it's not flooding into the vacuum line). I was under the impression that a misbehaving FPR would cause poor running rather than a no start -- is that incorrect?

Thanks,

-Lujo
'88 240 DL in Princeton, NJ

"Plugs look dry (is a wet plug actually supposed to be damp with gas, btw?)..."

Yes, sometimes saturated, dripping with gas. OK, plugs aren't wet, this isn't the cause.

"...under the impression that a misbehaving FPR would cause poor running rather than a no start -- is that incorrect?"

No and yes. A misbehaving FPR will cause poor running, but a REALLY misbevaving FPR will flood the engine in gas. But it'll also flood the plugs.

The confusing point is your previous comment about smelling gas at the exhaust. Apparently it's not too much gas.

Are you sure you have spark even when it refuses to fire up?

This isn't rocket science -- if you have adequate spark at the right time, and you have more or less proper fuel, it should start and run. So one or the other is not adequate.

Could the gas smell be coming from the 2 seconds it runs, but then it starves for fuel?
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Don Foster (near Cape Cod, MA)

> Could the gas smell be coming from the 2 seconds it runs,
> but then it starves for fuel?

That could certainly be the case.

> Are you sure you have spark even when it refuses to fire up?

I just pulled the first plug and disconnected the injector from its harness connector and proceeded to attach the plug to each of the spark plug wires while someone cranked the car. There was regular spark in each case. I don't have enough experience to be certain whether it looked like strong spark or not, but it was white/bluish and not yellow.

I guess this means that it's a fuel delivery problem. Is there a good way to test if the injectors are firing? I'm not sure I trust myself to be able to tell if they're buzzing or not, as the Bentley suggests.

Thanks,

-Lujo