need help with intermittent engine bogging

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under the radar
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need help with intermittent engine bogging

Post by under the radar »

car is a '79 528. it runs strong and idles smooth, but lately, it will be fine one moment and then the next it looses about 80% of its power under load and sputters. it doesn't stall out completely but comes close. and then the problem goes away, only to come back. i just want to get some basic ideas of what the problem could be.

parts that have recently replaced are, AFM, plugs, plug wires, cap/rotor, coil, oxy sensor, fuel filter and the ignition control box.

thanks in advance.
the early nineties called. they want their awesome back

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cpalmer
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Wild guess

Post by cpalmer »

I'm sure the "gurus" will give better advice, but I am going to take a wild guess and say it's the timing.

When you set it, did you do it at 2200 rpm with the vacuum hoses disconnected?

Kinda sounds like it may be way advanced, or retarded, but more likely advanced.

Just a thought.
under the radar
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Post by under the radar »

well, the timing was "set" awhile back and the car was running very well. this is something the car just started doing. i can try messing with it and see what happens. i'm thinking more like a bad transfer pump(in tank pump) but i wanna hear what the gurus have to say about it.
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alotawatts
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Post by alotawatts »

I think you are on track with fuel delivery problems. In tank pump problem should only happen at 1/4 tank or less....I may be wrong. Would help to know the pressure at the fuel rail.
Just curious is it a 4spd out auto trans ?
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Karl in KS
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Post by Karl in KS »

Check that the connector on the AFM hasn;t come loose.
I see you replaced the fuel filter already.
When my aux fuel pump died, the main pump made a buzzing sound like it was cavitating. it wasn't a loud sound, but I could hear it even when the engine was idling.
under the radar
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Post by under the radar »

ok, well to narrow it down a bit. i've swapped my afm with an old one i have. no change. i've check most if not all electrical connections and grounds. the main fuel pump is not buzzing loudly, actually i can't hear it at all while the car is running.
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Peter Florance
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Post by Peter Florance »

can you try another ignition coil and or module?
Peter Florance
First Fives.Org - The E12 Registry
1981 E-Street Prepared Euro BMW 528i w/3.5L & Megasquirt Fuel Injection
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under the radar
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Post by under the radar »

the coil is new (from bav auto) and i've swapped out the ignition module with another.

to tell the truth, i'm having trouble telling whether this an ignition problem or a fuel delivery problem. i'm going to try to fit a fuel pressure gauge.

ken M is going to let me try one of his spare distributors and i'm going to see if one of my friends has a fuel pump i can try.

the car idles smooth and fine, but as soon as i try giving it gas and letting out the clutch, it bogs down.

thanks for all the replies so far. this is making me crazy, i want my e12 back!
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alotawatts
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Post by alotawatts »

So problem happens warm and cold ?
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under the radar
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Post by under the radar »

yes, warm or cold its the same.
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Mike W.
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Post by Mike W. »

Timing wouldn't affect it only sometimes and quite that dramatically. Oh, I mean if you retarded it 20 degrees, it would run like crap, but like that all the time. Often stuff like this is the simple stuff, it just doesn't seem like it at the time. Pay attention to the tach next time it does it, if it reads normal, ignition is probably good. If rev's drop out of relation to speed, then it is an ignition problem. AFM would be my first guess, but I see you've already swapped it. Measure fuel pressure and go from there.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
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SteveinSLC
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Post by SteveinSLC »

Sounds just like my problem... and I have replaced almost everything you have with the same results. I haven't gotten back to mine yet... but I have a wire coming off of the ignition coil that looks suspicious. Ended up buying a used Camry to replace the E12 that can't get going. I agree... I want my E12 back.
1977 530i
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Post by under the radar »

well, i tried changing out the ECU and ignition control box...no luck, car still bogs and sputters. i also recently changed the transfer pump.

list of things i have changed
FPR
AFM
CTS
O2 sensor
Distributor
cap+rotor+wires+plugs
coil

i've cleaned all the grounds i can find. i just don't know what to try next.
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waltb
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Post by waltb »

How about the combo relay or the AFM fuel pump switch. The fuel pumps may be shutting down for a split second causing the stumble. I have had two separate problems over the years with both the AFM flap fuel pump switch going bad and also the combo relay overheating. It started out the car would only do this once or twice a month. Then it started getting worst and stranding me for a while until the car would randomly start up. I changed all sorts of things before finding the problem. In the E12 case I found the problem when it died close to home, I left the key on, and I ran home for a multimeter and found that the fuel pump was not running and I traced it back to the combo relay.

I also had a similar random stumble problem in an old Volvo I had. I found the problem in the Volvo because I had learned from my E12 and wired a test light in the pass compartment to the fuel pump circuit and one to the ignition feed and when it stumbled I noticed the fuel pump light went out. In the Volvo case it was a bad relay.

Walt B.
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Pierre
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Sounds like the Continuing saga of the random miss

Post by Pierre »

Sounds like the "Continuing saga of the random miss" that Brian has been battling for the past several months.
Read his thread for ideas. Problem is still unsolved.
Pierre in Camarillo
76 530i (3.3), 69 2002 (M20), 74 tii, 75 2002, 79 323i, 84 733i, 84 323i (S52), 91 318is, 96 318ti (S52), 97 Z3, 01 540i, 02 330i, 02 1150RTP.
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