rough idle after backfire


zbratt23
04-07-2004, 12:30 PM
he says, he started the car one morning , and it backfired once. since then, it idles very rough, if it stays running at all. you can still drive it as long as you keep your foot on the gas at all times. i've heard that the 633 csi's will do that sometimes (it's an 84) and blow a vacuum hose, causing the idle problem. i don't see anything outwardly visable though. is there a diaphram of some sort that may have been blown out?

KC Ron Carter
04-18-2004, 03:38 PM
if it backfired, it pushed that flapper past the normal closed and now it is hanging open.

The sell on E-Bay most days for $25 to $50.

You can swap with a known good one to verify.

Later,

pgerald
09-20-2004, 09:15 PM
I have upgraded the spark plugs, to bosch platinum t2 , high octane fuel but I'm still having problems, anyone to offer suggestions would be greatly appreciated.

pgerald
09-27-2004, 01:21 PM
he says, he started the car one morning , and it backfired once. since then, it idles very rough, if it stays running at all. you can still drive it as long as you keep your foot on the gas at all times. i've heard that the 633 csi's will do that sometimes (it's an 84) and blow a vacuum hose, causing the idle problem. i don't see anything outwardly visable though. is there a diaphram of some sort that may have been blown out?
is this flapper? in the mass air flow meter? is it fixable or do you have to replace it?

I have a 84 633 that is running very rich it won't idle below 2500 and back fires on deceleration, the plugs look like the motor is running rich, the plug wire seem to check out okay, and suggestions.

KC Ron Carter
09-27-2004, 04:12 PM
Motronic 1.1 uses a AFM, Air Flow Meter.

The sensor can be adjusted to correct for mixture.

http://normgrills.net/bcg/Injection.html#anchor41563757

Correcting Idle Fallout due to air flow meter carbon band wear on Ljetronic and Motronic models:
The problem of intermittent stutter at mid throttle, failure to hold idle, and the engine reponding when the throttle is depresses as if it were out of gas very often is due to wear on the carbon band within the Air Flow Meter.
The dealers will say replace the AFM. That can cost you a few hundred dollars or more.

Remove the black plastic lid.Notice the carbon dust on the pointer tracks on the carbon band.VERY GENTLY, ever so lightly lift up the pointer from the band using a small bladed screwdriver or thin hook tipped nose pliers.Blow the dust away, compressed air is preferred. If you don't have a compressor, see below.
To verify band wear or loss of pointer tension is the problem, holdthe pointer at about the place it would be at idle. If you are not familiar with this, try about a centimeter from the resting end. Then try to start the car. If just by pressing down on the pointer at the right spot gets the car to hold idle, then you have found the cause of your problem.
Now to regain tension at the pointer:
1. Notice the end of the copper pointer arm where it joins thepivot.
2. Notice where the arm is a double V shape, with an open slot between the inner and outer sections of the V
3. Press down on the arm, only on one side of the V, just away from the pivot until you just feel a little chance of it bending a bit. Nowdo the other side of the V, again just away from the pivot.
4. Pressing down GENTLY on the tip of the pointer with a fingertip, move the pointer forward and back across the range of movement of thec arbon band.
5. START YOUR ENGINE.
You may not get it exactly right at first, but once you get the ideaand can see exactly what you need to do, a little more or less pressure exerted on either side of the pointer arm will restore full contact over the full range of throttle motion.
You may then need to adjust the pointer position a tooth leaner or richer because of the slightly different resistance at any given point. This is done by moving that big black gear a tooth forward or backward.The gear retainer is easily lefted by a screwdriver. Be sure to put a dab of white-out or something to mark the original position so you can go back to initial setting if you need to.
The goal of this bending and repositioning of the arm and pointer is to both:
A. restore tension to the arm so it presses down sufficiently on the carbon band again and B. reposition the pointer ever so little further inward or outward so that it is now rubbing across an unworn part of the carbon band. You may then need to adjust the pointer position a tooth leaner because of the slightly different resistance at any given point. [If you don't have an compressor, then try this: Take a bicycle tire and tube, remove the valve; hose clamp a length of fuel line hose onto the valve stem; cut the stem and valve out of another bicycle tube, preferable the presta valve style as used on road bikes; hose clamp that second valve and stem to the free end of the fuel line hose. Now use a bicycle pump on the valve at the free end of the hose. Simply by pressing lightly on the tip of the presta valve, you can get precise controlled applied bursts of however much you pump up the tire to. That can easily be 120psi or more for two to three seconds on a road race tire, or 75psi or more for five seconds or so with a balloon mountain bike tire. ]

pgerald
09-30-2004, 09:35 PM
hello again, I tried using another air flow meter from another bmw with no change, the car wouldn't idle in fact it will stall out, I can't even get it to rev up. I noticed that when I unplugged the temperature sensor the engine would idle smoothly then once again begin to sputter, so I replace the sensor with a new unit but no change??. The fuel presure from the pump is good the o2 sensor checks out okay and I have replaced the fuel presure regulator as well, at this point I can't even move the car because I can't keep it running, any suggestions.

TrBean
11-14-2004, 10:06 AM
Just a thought.....in reference to the trb your havin...In the past i have had a rocker arm's break in the 6 & 7's..and it is almost always the 1st, 2nd or 3rd cyl ( from the front ) ..if it was a rocker arm it could cause the backfire.. to test this I remove the plug wires one at a time, untill i find the bad one....if its on the first 3 cylinders i just remove the valve cover and look at the arms...I have never had one go bad in the 4-6 holes...I think their was a oil deliver problem with the older engine's...good news is its not such a bad job to fix...the proper way is to remove the head.....there is a short cut...you remove the rocker arm shaft bolts..move the rocker arm shaft remove the broken one replace..retourqe and replace the valve cover...( dist,cam gear,time,cover need removed. if its the 1st cyl...you must also remove the rad or relocate it while removing the rocker ) ..**front pulley & cam position must be marked with a reference point to reassemble 4 correct timing**

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