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My 1998 Z3 has a backfire/stalling problem. Sometimes it occurs on start-up; and sometimes while driving (car can be cold or warm). Symptoms show-up when gas tank is low or full; high and low speeds; CEL is intermittent. It is a 1.9/M44 with 22K fair weather miles.
I have read numerous threads on different Bimmer/Z3 forums and find few "Z" owners have my problem; yet, stalling and misfires seem common on other BMW models.
Should I continue using the Z3/Z4 forum (not many threads); should I use "search", list topic, then post; should I use a general forum; or is there a more effective route? As I think about it, isn't a thread forwarded to a specific topic (found under search) regardless of it's origin?
Thanks Witeshark. I'll post a thread (in Z forum) on "unburned fuel detonating in exhaust". If this is the case, I may possibly be able to rule out poor fuel pump. Also, car is getting fewer mpg's since symptoms began.
What does it mean if you get a backfire in a cold exhaust?
Last edited by bimmerted; 07-18-2008 at 11:40 AM.
Reason: additional info
What is the cause of fuel being unburned in the exhaust manifold? My plugs are shadowy gray; no build-up. It seems each time I drive the car I find quick fixes and then driveability is fine. If it begins to backfire and act like it's going to stall, I simply slow down, rev it till it seems to clear (excess fuel?) then I'm good. At least for now.
On a different forum, a Z3 owner stated a new camshaft position sensor took care of his stall. I did change the o-ring on my cms but it appears the leak is not at the engine block, but rather where the insulating line comes out of the sensor (very slight, but enough to make the line appear oily).
I still haven't taken the car for diagnostics.
However, I believe I am getting spark. Car has relatively good pick-up. Not purring as she once did.
Here's another pattern: I'm driving the car around town (10-15 minutes), the auxillary fan comes on while driving at 15-20 mph. The temp gage is set mid range; suddenly I get my backfire and stall (if I let it).
Q -- is there a sensor (one in particular) that reacts to engine heat and causes backfire or stall. I ask this because I believe I have been searching down the wrong road. I recalled a slight performance change while cruising at Mich. Woodward Dream Cruise last year. The engine just didn't seem as smooth. Only I could tell as I knew the car. Point is, I thought my car was reacting to a storage problem. I now believe my symtoms began last August.
I have a similar engine in my 318, and the only time i had any issues even close to yours was, a. bad ECU(but i have the older ecu type being ODB 1, ruling that out for you) and a camshaft position sensor.
You may also want to check you vacuum lines and air intake butterfly. There might be build up somewhere causing a lack of air at certain engine speeds leaving you with unburned fuel? And only 22thousand miles?
what is the history of the car...? is this a recent acquisition for you?
i read through the posts... and from what's been said. i would take a look at the throttle position sensor/throttle switch. It's probably out of adjustment, or it has gone bad.
Dirty throttle body, a faulty AFM, bad air filter, even a bad 02 sensor, vacuum leak; or a combination of 1 or more of the above also causes the symptoms you complain of. And oh, on Z3, there's that variable control valve at the intake manifold that can cause probs too.
REASON for backfire: the DME ECU cannot "command" the variables in your engine to achieve a 14.7:1 air to gas ratio.
I'll ask you this... observe the stall. Does it happen when you accelerate?.. or does it happen a few moments after to let-off the accelerator? If u can answer that, i can help you pinpoint which part is faulty
Last edited by darkhorse737; 07-27-2008 at 10:44 AM.
Darkhorse: Sorry again. One thread would have been easier.
The abrupt/jolting stall is when i accelerate. Often when I push the car a bit through 1st and second. It has, however, stalled at a stop light. It has also acted like it was quitting as I was cruising at highway speeds in 4th or 5th gear.
As I mentioned in another thread, I will stick with one post if you like.
To ans your ques, I do have OBD ll system, but haven't had codes read. I know, I'm never going to get it till I do - right!- Just haven't gotten around to the 25 min drive to Autozone. Also wanted to do the forum route to avoid changing parts that are effected by simpler DIY - like vacuum leaks. I have a common prob. from what I read (but specific cause is not so easily pin-pointed)
Camshaft position sensor has come up on other forum. I changed my o-ring because I saw a leak- but, noticed the leak may be coming from point where wire comes out of CMS; and not from point of 0-ring.
If you have a minute, could you check my responses to Darkhorse. Did you have any of these symptoms? What wording did you get from OBD telling you it was the CMS? Also, am I safe from ECU probs. It sounded as though you were saying I wouldn't have this prob.
Darkhorse. I'm looking forward to hearing you explanation for stalling and backfiring. As you pointed out, I think we can rule-out fuel pump and vacuum leaks.
Since you probably help many people, I'll reiterate the steps I have taken to date:
-run two tanks of gas with Techron in each
-changed fuel filter
-checked and cleaned plugs
-removed bellow at throttle body and srayed/wiped butterflys (only top showed any signs of carbon - very little)
-one bottle of chemical to dry gas of any moisture
-changed air filter
-checked for vacuum leaks with carb spray, also sound check with short piece of garden hose (used like stethoscope)
-cleaned ICV; sprayed with carb cleaner. Sleeve action in ICV seemed smooth
-While ICV was off, sprayed into throttle body. some carbon build up but not restrictive
-spayed again behind ICV to check for vacuum leak (none apparent)
-driven car at higher speeds for 45-50 min.
-checked fuses connected with fuel (replaced with spares even though fuses were not broken)
-didn't check fuel relay; not sure which one it is or how to test
-changed o-ring for camshaft position sensor (still see leak but it's coming from bottom of wire; not where sensor bolts to the head)
CAR IS RUNNING WELL (smooth/no hesitation). Idle is 750+; and it starts within 3-5 cranks. BUT, the stall/backfire issue still exits. To reanswer your question, the stall that that makes you fell like you're going to go through the windshield, is usually during aceleration (1st and 2nd); but, it also happens while driving at steady speed; and sometimes (but not often) when I let off the peddle. In other words, I can't be 100% specific. But then you probably already knew that -lol. without codes read, will never get to the answer. or do you really think you got the ans?
SOOO, I'm patient. but can't wait to hear ideas on electrical probs. I'm not a betting man, but I sensing camshaft posiition sensor from other threads I've read.
It will take a few days before I get the diagnostics. I've taken on a project and I've been swamped till 10pm everynight.
I can't wait to take an uninterupted spin. I enjoy my Z a great deal.
Thanks for keeping in touch!
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