Stalling under load mystery?

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Jono B good
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Stalling under load mystery?

Post by Jono B good »

Hey so I've put so much money into this problem, but to no avail. I know I'm playing parts lottery as Brucey calls it, but I've taken Sonja to three different BMW shops here and they can't diagnose the problem. So I am humbly asking your long standing wizardry, and collective consciousnesses for a solution, so here goes.

My 1987 L6 stalls under load and idles at 500, I have replaced countless parts; all new belts, new battery, new fuses in fuse box, main relay, fuel pump relay, fuel pump(inline), fuel filter, cleaned ICV, new Bosch ignition coil, new distro cap, new NGK plugs gapped at OEM spec, AFM box(refurbished cleaned the wiper tracks made sure all contacts were cleaned and in good working order), new exhaust piping from manifold back to OEM muffler. I bought a second ECU but have not installed yet. As current one seems to be O.K.

In the AM cold engine starts right away, non issue, but in drive mode on the automatic the engine loses power and idle will dwindle down and the engine stops all lights on dashboard cluster light up. I bring key back to no start position, and she fires up right way in N or P. If at at a stop or light or anywhere it seems in drive mode on the highway idle drops to zero and and engine cuts out, I put it N and she starts up straight away. But I can only do this so many times before it becomes a no start issue. Which it has not come to as of yet. The scary bit is she will lose power at the most dangerous and inconvenient times like in the middle of the intersection on a green light. I am starting to think this car is haunted and trying to kill me. :-({|= I am almost afraid to drive the bitch now. Thank you in advance.

P.S. I never should've recently re-watched the original movie Christine. ](*,)

P.P.S. previous two owners could not solve the low idle/stalling issue either. The L6 ran right for maybe one month after a faulty electrical connection to ICV was found and some what repaired and valve lashed done in July, but idle was still low.
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baders
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Re: Stalling under load mystery?

Post by baders »

I'm just going to throw this in. Is your car running an aftermarket alarm/immobiliser ? This was my problem when I first bought LOCUTUS. I can't help but think you might need to go to a better indie BMW mechanic ?
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Jono B good
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Re: Stalling under load mystery?

Post by Jono B good »

No it is not running an after market alarm system, but it does have an aftermarket stereo and I did remove the OEM speaker fader switch/relay. I have been thinking about just reinstalling the fader switch. And there are only so many indie shops here. Allot of them are after the easy money, where they can just do a scan code and plug in the responding module. If that makes any sense?
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Brucey
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Re: Stalling under load mystery?

Post by Brucey »

It sounds like it might be one (or both) of two things

1) a badly set throttle body. You need to set it to 0.020" (0.5mm) clearance and then set up the TPS to match the new throttle body setting (as is perfectly well described in the manual). If this hasn't been done for a while then the throttle will be too far closed at idle (the linkage wears so that this happens, and nobody seems to ever bother lubing the linkage to prevent this wear... #-o ) . When the TB setting is wrong the ICV opens fully and the idle speed will be too low especially when the engine is not fully warmed up. The other thing that happens in this situation is that the transition from idle to part throttle becomes "as rough as a badger's arse"; depending on how the TPS is adjusted you will either get the throttle opening when the TPS is still instructing 'idle speed please' (which forces the ICV to go full stroke in a fraction of a second, something it isn't designed to do) or (if some half-wit has adjusted the TPS without checking/resetting the TB first) you will get a 'surge' as the TB opens and then it will nigh -on stall as the ICV slams shut. The one thing it won't do is run nicely. In any event the if the ICV is slammed into the end stops repeatedly then it can mechanically jam or electrically fail.

[NB apologies if this is obvious but there is only one reason for low idle speed; there isn't enough air getting into the engine. If the TB is set correctly and you still have a low idle speed, it is almost certain that the ICV isn't opening, either because it is not being instructed to or it can't for some reason.]


2) possible fuel starvation, probably caused by a dodgy electrical connection.

IIRC (do check the relevant wiring schematics to be sure) the fuel pump relay is wired through the OBC immobiliser relay. If the latter goes bad, it can cause the fuel pump to run intermittently and then stop running altogether. IIRC it is just a question of bridging two pins on the OBC control unit to eliminate this as a cause (although it does leave you with a non-working OBC immobiliser relay; big deal, few know it even exists, leave alone uses it) . There is more than one old thread on this.

For diagnosis of this fault you can put jumpers in place of the fuel pump relay. It isn't really safe to drive the car like this (in the event of a prang fuel could be pumped out into the wreckage at over 1 litre a minute, which is a raging inferno...) but it is probably OK to run the engine up to temperature in your driveway or something. If this normally causes the fault to appear, you will be able to find it this way.

On all M30-engined cars the TB needs checking and re-setting regularly, as often as about once every five or ten thousand miles, certainly every twenty. Intervals may be extended if the throttle linkage is kept better lubricated.

You could play parts-change bingo until the cows come home but if you have either (or both) of these faults then they won't go away. Potentially you could fix both of them in an hour, parts cost running all the way to a piece of wire and a couple of blobs of solder..... :shock: :wink:

cheers
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Jono B good
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Re: Stalling under load mystery?

Post by Jono B good »

Hello Brucey!! :D Thank you so much for the response brother! I really do appreciate it. Although Sonja is capable of toodling around town for a while, a short jaunt here, a small trip there. She is not at all up to her full potential, which being a 30+ year engine it never will be again. This would only happen with a fully rebuilt M30. Plus, plus all the other things. I will try to administer these operations with the help of my trusted shop (at this point) come the new year, as I do believe in his work, he has done the proper gap on the throttle body for now and will continue the work with TPM and then do the valve lashes at the end of this sequence of repairs. She may need a Idle Control Module (the small black box with the green cover and it resides next to the ECU). Once all is said and done I will update this thread with the results. For now I will stick to what I know I can accomplish by myself, regarding my sharks various DD needs.

Cheerio from across the pond. \:D/

P.S. as my Poppy a Briton who fought in WW1 would say "Don't let the bastards grind you down!"
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