M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: bmwman91 on November 28, 2006, 10:46:03 AM
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Alrighty, as some are aware (and some are experiencing), the car will sometimes seemingly misfire/stumble under low-load conditions, causing violent lurching. It will go away when you get off the gas, or give it lots more. It WAS totally intermittent and somewhat rare.
Well, this morning was the first morning I had to scrape ice off of the car this season. It started right up and idled fine while I was scraping the windows. After idling for probably a good 2 minutes I hop in and get ready to head to work. Just backing out of the driveway and trying to get to the end of the street was an ordeal.
The car would BARELY idle, fluctuating from 800 to near-stalling. The RPM got so low, the dash lights were coming on like they do in accessory mode. The powerband was virtually nonexistant after 2500RPM. Anyway, the car was still warming up. After about a minute, the car would idle fine again, and the powerband seemed to be back.
Now, the thing would seemingly misfire (seemed more like not at all...no bad noises, just an engine stumble). It would occur while being at just like 1400RPM momentarily to move the car in the metering light line. After it warmed up, it got better.
Now, on the highway...ANY time I was at low-load partial throttle the car would start feeling powerless and lurch violently from the "silent" misfires lol. If I got off the gas, all was well. If I gave it MORE gas, probably a throttle position of 50% or more it was fine...no misfiring. But man, at low-load part throttle it was a real bit*h.
I have been unable to diagnose the problem when it was not as bad, due to its rarity and it hitting me unexpectedly. It has never triggered a Check Engine light. This morning I FINALLY got a little evidence. When it began lurching, I just kept the gas pedal in place and observed my gauges during the problem. The MPG indicator was fluctuating (and seemed to be at a VERY low position considering my foot's position) with my unmoving foot. Soo....that says to me the problem lies in the fuel system. The MPG meter is basically a direct teller of injector duty cycle. If it was saying I was getting really bad mileage and moving around...that says to me that the problem is fuel pressure.
The hypothesis:
Since it was saying that my mileage was very low, that means the injector duty cycle was set very high. Considering the vehicle speed and throttle position, it wuold only do that if the fuel pressure were dropping and it was trying to compensate by opening the injectors longer. So, that would lead me to believe that the fuel pressure regulator is bad. If it was the pump, the problem should get worse as I open the throttle as it puts more load on the pump. The regulator (if it is the case) seems only to be working under high- or no-vacuum conditions.
Anyway, help me out here. Do the FPR's go bad on these cars? Is my theory crap? Shouldn't this be triggering a check-engine light???!!
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a few weeks ago, we were working on my buddy's e30 and forgot to re-connect the mass air flow sensor wire. the car was giving us the same(or at least sounds the same) problems you described. i know this has nothing to do with your theory about the FPR, but it's the only thing i got. inspect the wireing i guess i'm saying, or maybe the mass air flow sensor is bad, or, more than likely, i have no idea what i'm talking about... good luck
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Well, easy way to to test fpr is to get a gauge and place it inline. If you wanna be ghetto, you can probably put something together from your hardware store or just get one from SummitRacing or Jegs.
Is it possible that one of your Injectors are crapping out? I ran into a similiar problem with a different car where the injector was only working correctly above a certain threshold. At partial loads, it wasn't working correctly.
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It could be the injectors I suppose. I am running S50 ones and I think the M42 stockers are around somewhere. Lord only knows why they would work at higher DC's, but not at lower ones. I have a spare FPR somewhere in the back yard on an extra fuel rail. Maybe I will try swapping them tonight. Hopefully the car will still be running like crap when I get home so I can diagnose this. I hate how it was intermittent...I just KNEW it would act up again, probably when I REALLY do not want it to!
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I wish I had a bunch of spares laying around for diagnostics and maintenance. My friend and old racing buddy has a salvage yard with this sign, "If you bought a part you didn't need, you now have a spare." I've suspected sometimes that repair shops replace parts until they find the one that fixes it and then tell you it needed them all. Especially with fuel injection and electronics.
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Both my 318is had a problem similar to that. My first one had it more often and at any temperature. My new one only does it if I stop the engine and start it while it's still hot or at 1/4 temp. I press the gas pedal to the floor and the rpm barely goes up....until everything returns to normal and the car starts to accelerate like it should. Then it doesn't do it until I stop the engine again. I'm very eager to see a diagnosis that's got some research behind it. I've tried a few things like changing the gas pump, gas filter, use injector cleaner...nothing worked.
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Well, spent the evening swapping the fuel rail & injectors. The car is just as bad as it was this morning, minus almost stalling from idle. I had a fuel rail laying around from the wrecked car and some stock M42 injectors. I took outt he S50 ones...the car DID idle nicer after the ECU reset so I guess the M42 injectors were good to go back to. Grrrrrrr....WTF! Next up is swapping the ECU I guess, perhaps I will check the TPS output first though. Son of a bitch, I need a running vehicle!!!
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I think my car's developed a simular thing, is it quite loud and sounds like a shuddering from the front?
I'm taking a stab here and going to say its a bad AFM, but then you've got a MAF dont you? mmm... could be a fun weekend....
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Nope, still running the AFM. I was going to put the MAF converter on yesterday, but I do not want to until I fix this issue.
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test all the sensors into the motronic dude, and do a diag too. TPS/CLT sensor/crank/cam position sensor etc are all likely candidates. I know a lot of these seem unlikely, but i've seen, in particular, failing cam/crank sensors give less than reliable output, CLT spikes (normally ground issues) and so forth. you not got a diag lead? spose ECU is possible, but i've never heard of a failing M42 ECU.
I'm not convinced by yor FPR theory, have seen FPRs not give great pressure due to knackered diaphrams and slightly affect max performance as a result, but thats about all. nothing as severe as you're describing.
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I have a multimeter & oscilloscope. I guess I can go freeze my ass off in the garage after work lol.
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I'd say thats a faulty coolant temp sensor or a bad connection to it. Sounds like the same thing that happened to my daughter's 84
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Hokay, to I messed with the TPS tonight. When I got home from work i just disconnected it and drove...things seemed better, and it only stumbled under acceleration a couple times, but was not consistent. I plugged it back in and it ran almost perfect. Grrrr.
I removed it and took it apart anyway, and adjusted the brushs so they would DEFINITELY be making contact at all times. I drove it for a good 30 minutes on the highway, making sure ot be at the RPM and throttle conditions that always cause the problem. I had ONE misfire...ONE. That makes me mad...the problem is "hiding" again. So, next up is the AFM on the test list. It is the only other thing that would be throttle and RPM dependent. Maybe the carbon track is having problems.
I will check the CLT sensor too, thanks for the heads up!
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Well, I just test-drove it with the new MAF converter on...no weird stumbles, buuut it may still be hiding from me. Only time will tell. I couls understand the AFM wearing out anyway.
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I just took it around the block before work this morning and no hiccups. Maybe the AFM was bad...the MAF was still on it. Then again, I was in the garage alst night so nothing got too cold. I will leave it outside tonight.....
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Just worked out the problem with mine, cracked idle bypass hoses - some of them are a bit fiddly to get to, but for the moment i've just covered them in duct tape until BMW open here in oz again on monday morning.
Its fairly easy to miss it and i was just about to start ripping the throttle body apart and then i saw the cracks, taped them up and seemingly its running fine again... dont know how i missed them the first time!
Hope it helps!
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I will check that out. All looked good when I had it off, but I may have missed something.
Still have to check over the coolant temp sensor.
I THINK I felt a little shuddering when I was driving with the MAF, but it could be bumps in the road combined with my paranoia!
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Hi, my 318is e36 has now same problems as your: idle low and stalling, stumble at low load and poor output... all it's beginned in a gear change. The car after the change of gear has stalled and shut off. Now it's near impossible to drive. I've checked the plugs, removed the cat and started without it. I had a RRFPR and the car was extremely rich. Now I think that the cat is clogged and the engine is full of carbon deposits. There are misfires and the car sound like a lawnmower:confused: like a two stroke and very irregular even at idle.:eek:
help me
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The other thing that i just found on mine is that the exhaust is cracked at the front of the muffler - thats also causing some problems with backpressure and what not!
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Any news Bmwman91? Did the MAF fix it?
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have you replaced your fuel filter lately? Might be clogging things up and forcing the car to push more fuel through creating all sorts of instability.