Another m20 no start thread...

[quikveedb2]

'87 325is. I started having some issues last fall; the car would run fine & suddenly die at random, then restart no problem until November or so. Then one day leaving a g/f's place the car started, died, took forever to start again, and died 2 more times as I limped it home, where it has sat & has not started since. I have a winter beater so no biggie, but spring has sprung & I need to get my beloved e30 back on DD duty.

The car will turn over no problem, usually will catch for a few revs, then die and will not catch or start again. New battery, plugs, cap, rotor, coil, fuel pump relay, Fuel filter, main relay, CPS tested within spec, voltage to dme is good at the harness, continuity on all dme grounds is good as well. I do not hear the fuel pump(s?) running when the key is in the on position, or during the test in the bentley. Can someone tell me if I have 1 or 2 pumps? Build date 3/87. It's a weird car though, mid switch from early to late stuff I think. I used to be able to stomp test but my light for the check engine light burnt out, on the days off to fix list for now. The car also did not pass the tps switch test, particularly the wot switch portion of the test. The car used to throw a wot switch code when the cel
light was not burnt out but the car still ran & drove fairly well. I'm goin' to re-adjust it, but I don't see why the wot switch should have anything to do with just start & idle conditions. Side note, the car was pretty low on gas when I really had issues the last day I drove it in the fall, is it posssible that the fuel pump overheated or sucked some shit up from the bottom of the tank & burnt out? Anyone have some bright ideas where to continue my testing & troubleshooting?

[jlevie]

Understand that the fuel pump is controlled by the DME and only runs when the DME sees timing data from a rotating engine. So not hearing the pumps when the key is on is normal.

Your car has the 55L tank with an in-tank transfer pump mounted on the right side and a high pressure pump mounted just forward of the left rear wheel. A failed transfer pump will cause starvation issues when the tank drops below 3/4 full. But either or both pumps could be bad. Run the fuel system test suite in the Bentley manual to find out if you have a fuel system problem.

Unless someone swapped out the 153 DME the car came with for a 173 (or later) the stomp test won't work on this car. Even if the DME has been swapped, if either switch in the TPS isn't working the stomp test won't work. The odds are that oil that seeps into the TPS from the throttle body has destroyed one, or both, of the TPS switches. Meaning that you need to replace the switch. I always drill a 3/16" hole in the center of the cover of the TPS to give the oil that seeps in a way out.

My guess is that you have a fuel system problem. There are other possibilities, but rule that out before considering other cases.

[Sir Smirnoff]

maybe your fuel injectors are stuck open. Could also be the o2 relay. check that by pulling the fuse. If it works, maybe you're onto something.

[quikveedb2]

Cliffs notes: I need a schematic of the main relay, please.

Thanks for the detailed response. jlevie! The car definitely returns codes with a stomp test, I'll check to see what dme I have. I did a little bit more testing yesterday and this what I found; there us power to the main relay from terminals 30 & 86 of the main relay at the relay panel, but I only measured 1.8-2 volts at the idle air stabilizer valve. This was the case with both the new & old main relay. However, with the old relay installed I noticed that with the new relay installed the icv did not buzz as it should (key in on position, obviously), and with the old relay installed it did. Out of curiosity I cranked the car and low and behold it fired right up & idled like a champ. I reinstalled the new relay, and bam, no buzz from the icv, and no start. Old relay back in, icv buzzing right along, fired back up no problem.

Problem solved, right? Negative. I let the car idle for a few minutes, and it suddenly died again, and would not start again. So, at this point I'm thinking 1. The new relay is not the right one and 2. The old relay is going bad. When the car was idling I could hear the fuel pumps running, or at least the one in front of the left rear wheel, so checking to be sure the main relay is working seems to be the first logical step. Opinions? TIA!

[jlevie]

It does sound like your new relay is the wrong one. Is it a 5-pin like the old one?

The engine dying after about 5 minutes of idling could be a problem that is only apparent when the DME switches from open loop to closed loop mode. But on general principles I'd recommend getting a new main and fuel pump relay (by part number). The big difference between open an closed loop mode is the use of O2 sensor data by the DME to adjust A/F ratio. An aged (useful life is not more than 100k) or bad O2 sensor could upset the A/F to the point that the engine won't idle once the DME switches to closed loop.

[quikveedb2]

Thanks again. Yes, it is a 5 prong relay. I'm going to look into the main relay asap. The fuel pump relay was replaced last fall, I also kept the old one, which was working at the time of removal, so I can use the 2 for comparison purposes if needed.

Since the dying before the (wrong) main relay was installed was intermittent would that suggest a bad O2 relay? Could a bad O2 sensor cause the same intermittent issue or would it just make thecar not run at all? If I unplug the O2 sensor or remove the fuse as suggested above, and that car runs through the closed loop mode is this an indicator of a bad relay and/or sensor?

[Sir Smirnoff]

if you unplug the o2 sensor the car always runs in open loop, never closed loop. The o2 sensor should not be on a relay as far as I am concerned. The voltage and amperage is so low that it is generally ran off of the ECU 12V or the 12V rectified hot without a relay. a bad o2 sensor could be the issue, but i doubt that because the o2 sensor is not activated when the car is cold. It sounds like more an injector/fuel issue because you obviously have spark. Have you checked your fuel filter? Even if the pump is good the filter can get clogged.
Does the car sputter before it dies? Does it attempt to catch itself? Did you try "priming" it by pumping the gas pedal before starting and or during?

The only other thing I can think of is that your Throttle position sensor is bad. I suggest you test it with a voltmeter. If your TPS is screwing up, your fuel delivery will be shit.

[quikveedb2]

if you unplug the o2 sensor the car always runs in open loop, never closed loop.

this makes sense, so if the car starts & runs without the O2 sensor attached that is the culprit.

Have you checked your fuel filter? Even if the pump is good the filter can get clogged.
Does the car sputter before it dies? Does it attempt to catch itself? Did you try "priming" it by pumping the gas pedal before starting and or during?

Fuel filter was new a year ago. The car does not sputter, it just falls flat on it's face dead. The gauges die as well. Priming the motor has no effect. TPS failed the WOT portion of the bentley electrical test, but had failed before all this no start business, and the car still started, ran, and drove fine.

[Sir Smirnoff]

[quote=quikveedb2;1948487]this makes sense, so if the car starts & runs without the O2 sensor attached that is the culprit.

Yes you are correct.

[StereoInstaller1]

Ok, before the misinformation gets too deep around here, let me clean this up:

1. TPS: on Motronic 1.3 (173 ECU) or 1.1 (153 ECU) the TPS is NOT variable: it reads at WOT only, so ignore that. TPS cannot make any change unless the car is WOT.

2. O2 sensor: Heated (4 wire) means it has a relay, but only for heat. An O2 sensor does in fact read from the reference 12V, but in the case of M1.3 or earlier, it is only a "tickler" sensor, and does not greatly affect the running of the motor.

If you had a nice smooth running M20, disconnecting the O2 will makea difference, but not night and day, only a minor difference...except in fuel economy. There, it will be as much as 20% difference...so your issue isn't the O2, either.

3. Wiring diagrams can be found at www.wedophones.com: This is the BMW ETM, the Electrical Troubleshooting Manual. Be prepared for a serious hassle, some are even in German! You will find pretty detailed schematics ofr every circuit on the car, but you will feel the pain of those of us who have been doing this professionally for years: colors will be in one section of the manual, pinouts and other values in another section.

Dual monitors make this part SO much easier!

Back to where to find it: go to www.wedophones.com, then look to the top right corner of the front page for "MANUALS", then look for "Automotive" and I bet you get it from there. I recommend you download, as it may or may not be there when you go to look again.

Now, back to your main relay issue; all BMW relays are a non-standard configuration....except one, and that would be the main relay. It is a normal 5 pin relay all right, but not the normal SPDT as are used all over the world in which there is a common (30) a NC (87a) and a NC (87)...instead, this has a SPST, but with 2 NO (30) terminals...so it looks just like any normal relay, but has no "87a" connection.

That is likely what you have as your "new" relay...and likely as not your old main relay is bad.

So, good luck!

Luke

[quikveedb2]

Thanks for clearing all that up Luke, I was fairly sure the tps was not the issue. I've got the next few days off from work, so I'll start by getting the right main relay in and go from there.

[quikveedb2]

Update; got the correct relay from FAP99, it was like 16 bucks, and it seems to have solved both the intermittent no start & stalling issues, thanks to everyone for their input! now to fix the check panel that just quit working & move on to some cosmetic & comfort issues.