No fault codes in DIS for limp mode

[braincat]

Although I've experienced limp mode in my 850 many, many times over the years, for the first time I've had no fault codes found using DIS. Normally I'll get something about an ignition failure on one bank or the other, but what might cause half the engine to shutdown without recording any problems?

[Wuffer]

Dead fuel pump

[braincat]

Cheers Wuffer, is there a reliable way to test them? If fuelling's involved could it be as simple as a blocked filter?

[Wuffer]

Cheers Wuffer, is there a reliable way to test them? If fuelling's involved could it be as simple as a blocked filter?

Two ways to test pumps - one is to pull right side rear seat to access the pumps and remove the 3 pin plug to the pumps. Center pin is ground so supply 12 v to each pump and see if you can hear them run. No sound = dead pump. Second is to pull fuel lines, one at a time from the fuel rails at the back (firewall) side of the engine and crank the engine. no fuel squirty out = dead pump or.... plugged filter.

[braincat]

Quality info, cheers chap.

[Ledo]

My experience is the same as Wuffers. Had both pumps die on me and it throws no codes. It even works very steady, just no power.

If you have a spare, open up one fuel relay and wire a small switch connecting the center pin and the pin to the back of the car IIRC. That way you can run the fuel pumps very easily.
One fuel pump is connected to the fan for EML and DME cooling, so don't be surprised when you start it. It is really easy to diagnose this, replacing the pump is a bit of work tho.

[shogun]

I do it on my 11/88 E32 750 with a short wire, no ignition on, remove the fuse box cover, one end of the wire on the B+post, and the other end on tp of the fuse # 23, and then #24, just for a second, you can hear the fuel pumps running (because the engine is not running) and even can hear the fuel run thru the pressure regulator when the fuel goes thru into the fuel return line.
fuse 23 = called injection electronics (DME/EML)
fuse 24 = called injection electronics (DME/EML)

before doing that, squeeze the fuel feed lines to the rail and do the same after jumping the wire, you will feel the difference.
That is enough for a quick and dirty test.
Check the ETM which fuses are for your engine and built year.

[braincat]

Thought I'd solved this; changed the filters and for a few days it ran lovely, with increased mpg so they obviously needed doing. Went limp for about a minute on the way to work today, then sorted itself and was fine for the remaining 20 minute drive. I have tested both pumps and they operated fine, though with an intermittent fault I guess that doesn't prove much. Before I jump in and replace them though I did notice that just before it went limp there was a distinct fuel smell. I've heard this could be a sign of a bad fuel pressure regulator, would the fpr be capable of putting the car into limp mode? The smell went away as soon as the car clonked into limp and didn't come back after it started working properly again.

[braincat]

Still no joy, filter, pumps, hardlines all replaced now but still intermittent limp mode. Anyone got input on the fprs? Racking up the bill now but can't think of anything else that would cause this.

[Mikekugel]

Have you changed spark plugs recently? If so, are they 1000 Ohm resistor plugs, like the NGK BKR6EK? Have you inspected your distributor caps? It could also be a cracked solder joint on one of the relays near the DME's, or so many things. Good luck

[braincat]

Still limping! new fuel pump, fuel filters, fuel hardlines, new plugs bkr6ek, new fpr on problem side, swapped over pump relays and mafs, still dead on 7-12. Really annoying as it goes limp for 1-2 minutes max at random while driving then sorts itself out. Gonna try swapping the ecus next and failing that I guess I'm just gonna have to ignore the fact that DIS and Inpa are showing no faults throughout and start swapping over the rest of the ignition components. Both distributors, arms, and coils were replaced less than a year ago so I'll be most peeved if one of those has gone!

[braincat]

So after chasing the problem since early March, and a few hundred spent, I've finally fixed it in half an hour for free. Failing cylinder ID sensor. I guess I expected when these start to go that DIS would show the ignition fault cylinders 1-6/7-12 but obviously not! The car went into limp 4-5 times every day, for never more than a minute, but no fault code was ever triggered. After exhausting all other possibilities I went back to basics and after swapping the lead set over it finally jumped sides (with a week of added confusion after one of my brand new fuel pumps failed!), and I fitted a spare lead with sensor. I suppose unless these sensors completely fail then no fault gets logged. Nevermind, at least I've switched out some old parts, even if they were working ok. Maybe I should write a book called Living with Limp Mode. Should get quite a few purchases from the M70 community, plus with a title like that I'd probably get a lot of accidental purchases from guys with ED...

[cartoonz]

They've got pills for that now...

[braincat]

What, you put them in the fuel tank and it stops dying on me?