Difficulty Level: 1 Difficulty scale: Adding air to your tires is level one Rebuilding a BMW Motor is level ten
This article is the one in a series that will be released in conjunction with Wayne's upcoming book, 101 Projects for Your BMW 3-Series. The book will be 256 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 350+ full-color glossy photos accompanying extensive step-by-step procedures, this book should be a staple in any 3-Series owner's collection. See The Official Book Website for more details. The book is due out in October 2005.
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Here is a list of what to check if your car is backfiring constantly or if the car is not running right.
Ignition box (CDI/CDS)
First thing to check is that the ignition box is making squeling sound while power is on, this indicates that the high power voltage is produced.
If there is no sound check that the ignition box is getting correct voltage (Check the manual which terminal) If the voltage is much under 12V the ignition box will not sound "healthy". If you have heard the sound while its working, you know the difference.
High voltage terminal should be reading 4-5V, and when measured with oscilloscope there should be this 400-500V spike when terminal C is connected to ground.
Ignition coil
Ignition coil is simple to measure. When measured with ohm meter the primary coil windings should give reading of 0.3-0.6 ohms. Secondary coils should be near 600 ohms.
Check that the wires that are attached to coil are correctly connected
Never use conventional ignition coil with CDI/CDS system
Ignition wires/connectors
Check the wires with an ohmmeter that they all conduct. Copper wires should give very low readings, refer manufacturer information on other types of wires
Wires could leak the "spark" to ground therefore diminishing the spark that goes to spark plugs. Putting tape on the wire to prevent leak won’t help. Replace the wires, they are cheap.
Resistors (plug/distributor caps) need to be measured, they should all be in +/- 10% ohm range of each others (2k ohm on each end is normal)
Resistors are not needed, but dismissing of those may cause radio interference in stereo equipment or other digital instruments.
Spark plugs
Check the plug condition visually and clean the plugs with brass brush.
Check the gap between the electrodes (should be 0,6mm or near)
Plug insulator may be cracked and thus "spark" is leaking to ground.
Breaker points
Check visually that the breaker points open enough (refer to manual) when manually turning the engine (BE SURE THAT THE IGNITION IS OFF!!)
The breaker point contacts should be clean and even. If there are any spikes or holes with on the contacts, replaec the points with new ones.
Check with "light pen" that the breaker points open at right position
Breaker point gap is directly connected to dwell angle. To be sure that the gap is correctly set, measure the dwell angle with correct meter (many multimeters have this nowadays).
Vacuum advance/retard
While distributor cap is off you can check if the vacuum advance system is working
Remove the hose from the carburetor and suck it (with your mouth). The breaker points should be moving a bit
If nothing happens the breaker point advance/retard system is stuck. Lubrication usually helps on this one.
If the breaker points are moving just fine when moving with hand, the problem could be the vacuum unit. When aging these usually break and should be replaced.
Carburetor
The carburetor could be getting dirty and clogged so the mixture is not right, if possible check the jets and emulsion tubes that they are clean. With weber carbs the idle and main jets are easily removable, they are at the opposite side of acceleration pump. Even if these look clean, clean them with compressed air. Don’t poke them with anything metallic, the jets might get damaged and the jet sizing is not correct anymore. If the jets are very much covered in oxides you could soak them in some solvent overnight or try cleaning them ultrasonic washer.
Air leaks can cause backfiring, the leaks cause that the engine is getting too much air and so the mixture is not correct. You can either install new gaskets to carburetor or use some gasket adhesive to correct the situation. Don’t use any silicone based substance because they can’t stand the heat+gasoline combination, even though the markings on the side of the box indicate so. Besides, when you put the carburetor back together some silicone adhesive could get instantly in carburetor and from there to the jets and emulsion tubes.
The gasket between the engine and the intake manifold as the gasket between carburetor and intake manifold might be leaking. These are usually made of graphite or other material and need to be replaced with new ones.
The fuel mixture may be too lean and cause backfiring and uneven run.
Comments and Suggestions:
MROSS
Comments: how do remove ignition cylinder only, on a 1993 BMW 325i 4 door sedan 5spd inline 6 cylinder. The key just turns in the ignition where key inserts. the ignition is stuck in the acc mode. Its stuck between off and engaging starter.So I had to disconnect positive terminal in the dark so I would not kill the battery. The steering wheel is in the lock position so I can't turn tires to tow out of very steep driveway. I was told that I need a very skinny, narrow tool to insert along ignition and it will slide out easily.
May 8, 2012
SanWhor
Comments: My 1994 325i misfire, Peake scan tool read code 19= coil #5, I replaced a set of the spark plugs and one bad coil and reset the code, the problem still not fix, I checked the coil plugs with the ohm meter the #5 coil plug "black wire" has read "xxxx" the rest of the five coil plugs "black wire" had no read "0", Please help.
April 28, 2012
damien0222
Comments: hi i have a 1987 318i bmw.. she starts up perfect idles perfect but when driving and the revs exceed 2000 it has a sudden miss or pinging as they say.. i have changed the plug leads.. the coil... the rotor... any ideas of what else may be the cause?
March 13, 2012
RMP
Comments: I replaced the cold start valve, because it took so ong to warm up. now its about three starts before it will idle at 8 to 1000. Could the valve be dirty? and should I replace the fuel filter. Its fine once warmed up.
January 16, 2012
mahi
Comments: have 1998 m-3 that I swap engine. My problem is that when I started the engine, it goes ful trottle. Could I have connected the sensor incorrectly?
January 15, 2012
jrbaly
Comments: I am having trouble with the car starting. I have a 1992 bmw 325. Went to start the car this morning and it won't catch. It's turning over but won't ignite. Battery sounds weak though.
December 29, 2011
Followup from the Pelican Staff: Your 92 should be putting out trouble codes - check out our article on fuel injection trouble codes for more information. - Wayne at Pelican Parts
JJ GA
Comments: I HAVE 1987 325E WENT I START THE ENGINE IT LACK THE FULL POWER I HAVE TO START THE ENGINE ABOUT 3 TIME TO GET FULL POWER WHAT WOULD COST THIS
December 18, 2011
Followup from the Pelican Staff: It could be many, many different things. I would first start looking for vacuum leaks. It may also be caused by a clogged fuel filter or a failing fuel pump. Those are just my first guesses off the top of my head. - Wayne at Pelican Parts
sas
Comments: i have a 2003 540i. One morning i went out and turned the key and heard one click. I put the battery on a charger for a night tried again and just heard a single click. indicators say battery is ok. could it be the starter?. any help would be appreciated. thanks
November 9, 2011
e36 danny
Comments: im having a problem with my car i changed to starter due to the old one going bad but my car still wont turn on it just cranks. what should be the problem
November 8, 2011
wynn
Comments: My '95 M3 ran hot while in traffic but not all the way to the redline in the gauge. I made it home but when i tried to start the car she wouldn't turn. No clicking of the starter even. I have power on my instrument cluster but not on the multi-information display or on-board computer. very dim lights on the climate controls. When you turn the key nothing happens. I need help!
October 17, 2011
Jake
Comments: I have a 01 z3 3.0, it has no power at the fuel pump, power on the 30 pin on the fuel pump relay, power on the 30 pin on the dme relay, no power on fuse 13. Tried jumping the DME relay from the 30 pin to the 87 pin, with nothing.
I am at a loss for what else to check, an help?
October 1, 2011
Rod
Comments: Have a problem with 90 BMW 525i. Just had the intake manifold gasket and spark plugs replaced to cure an uneven idle and loss of power when moving away from stop lights. Engine builds power very slowly. Check engine light comes on between 1500 - 2000 rpm. Engine cuts out momentarily at highway speeds, car vibrates. Any ideas on this problem?
May 8, 2011
Batman68
Comments: I have a 92 325is manual and it completely will not start. I turn the key and all the electrical comes on but the engine will not turn and there is no cranking sound heard. The battery is fairly new and putting out the correct voltage. I also tried just starting with my other vehicle and no responce. Please offer suggestions. Thank you!
March 1, 2011
Followup from the Pelican Staff: It could be one of many things, but the first thing I would look at is the ignition switch - these tend to fail after many years. - Wayne at Pelican Parts
rags
Comments: i have an 1981 320i bmw that just stoped runing i put new spark plugs/ wiers , cap, roter and coil it started agin and ran for a few minits and wont start agin and has no spark thank you if you can
January 6, 2011
Followup from the Pelican Staff: It's very tough to diagnose problems like these over the Internet. However, no spark may be related to your camshaft sensor - I would take a closer look at that before moving on. - Wayne at Pelican Parts
et
Comments: i have a 88 735i my batter went dead put i new one in and know all it wants to do is turn over and the horn blows but will not start i dont have a ownrs manel for it how can i get is started
December 26, 2010
Followup from the Pelican Staff: Sounds like trouble with the alarm system. I would try to disarm the alarm, and that might help. This is one of those issues that are probably impossible to diagnose over the Internet. - Wayne at Pelican Parts
topgunn
Comments: need help unstalling the ignition switch on a 84 bmw 633csi.
Thanks.
Terry
November 30, 2010
odi
Comments: I go to start the car and the key turns over and i hear what sounds like a celonide clicking, and the car wont start. if i hold the key it clicks cont. battery is fully charged, coded key seems to be working, tried the spare with the same results, starter gone out, just like that?? any help would be great thanks
November 18, 2010
Followup from the Pelican Staff: I'm guessing that the battery is dead. You may think that it's fully charged, but it doesn't sound like it's allowing any current to discharge. I would replace the battery first and then go from there. - Wayne at Pelican Parts
amsterdam
Comments: we changed the pcv on 2004 325i oil separator put everything back now the car has no spark to the plugs.please help
November 12, 2010
freeroamer
Comments: i have a 1984 bmw 318 i 1.8L jetronic 11/84 production date single overhead cam with the 0080 distributer,i have for timing i know it should be 15 degrees before tdc,it there an easy way of knowing when i have it set on the mark for tdc by looking through the bell housing?what should i see for it to be right on it? i have replaced the pulse sender today ,replaced the ecm with a rebuilt,n 4 fuel injector,2 of the fuel injector were not on the correct injectors,i am getting to signal from the distributor, at the icm also i am get current at that location,i have also replaced the si board with a batteryless one,i have fuel getting to cylinders and the cold start valve is giving fuel in intake,the fuel injectors i put new upper and lower seals,also have checked for continuity at icm at ground and + terminal and had continuity til i took off the wire on temp sensor near distributer,the car was running at one point til i got 2 plug wires backwards.now the engine just turns over and does n't start i think i need to get a bwd coil, as i have a msd coil,but need exact timing mark locations,also used a jumper for the clutch switch because it is bad.
November 11, 2010
Followup from the Pelican Staff: It sounds like you have a lot of stuff going on. I would post this issue in our forums so that a bunch of people can take a closer look at it. - Wayne at Pelican Parts
luis
Comments: I have a 96, 5 series, the car dont start,I have a good power from the batteria.
Comments: I have a 1989 535i bmw e34. I recently replace the head and now i dont have spark to the spark plug wires. It was running before i change the head and the only thing that its different is my ignition key,because i lost the original key and the key that i have rite now i bought it from the BMW dealer itself, could that be the problem? Please please help ! ! ! !
April 14, 2010
Pig
Comments: I have a 95 325is. When I am under heavy acceleration, my car begins to mis-fire around 3500rpm to 3800rpm. After that rpm range, the car seems to be fine. I have replaced the wire set, the plugs, and the coils. I have checked compression. The results were 230, 230, 220, 225, 237, 230. What could be the cause of my power-loss from 3500rpms to 3800rpms?
March 5, 2010
TheStigg
Comments: i am getting a vibration, like a misfire, at about 2300 and 2700rpms and i think it is messed up wires but im not sure because it isn't a constant misfire. i replaced the spark plugs and the valve-cover gasket because of oil it the spark plug holes, so im guessing it is the wires. Any suggestions?
February 18, 2010
FikMak
Comments: I have a 92 bmw 325is. Recently, Sometimes when I start the engine, the needle on the odometer stops working. Both the needle for the radial, speed and fuel gage stop working properly they shake like crazy by where they're sitting. Inspite of this, the engine starts. Then everything goes back to normal. Then again it goes crazy etc..The other day, when I started the engine, all of a sudden, both sides of the window and the sun roof stopped working. I checked the fuses, but they all work just fine. Please advise. Your input will be highly appreciated.
November 25, 2009
red bmw 1991
Comments: how do u check a coiloff of the car if i have power going in the coil but no power coming outof the coil is the coil bad or i need to check something else
November 15, 2009
red bmw 1991
Comments: have a problem my 1991 325i dont have spark check the coil no poweror spark whats wrong
November 15, 2009
Griffin
Comments: I have a '98 328is. Recently I've noticed that at highway speed and between 2-3,000 rpm in 5th gear the engine will begin to vibrate and the car looses power. Once this starts the car will continue to run poorly in any gear or rpm. Restarting the car usually fixes the problem temporarily. Bad ignition coils/spark plugs? Thanks!
Comments: Iown a1987BMW325I and i am having problems with hard starting. Sometimes the car will start in one second and other times it takes a little longer.
October 26, 2009
Followup from the Pelican Staff: Start by looking for vacuum leaks, that's the number one culprit in these cases. You can also check for fuel from the injectors when you're starting - there may be some clogs in there. Replacing the fuel filter *might* help, I have seen this happen before with a clogged filter. - Wayne at Pelican Parts
beemerhog
Comments: one other item never seen before until i tried it. if your having random stalling issues with the engine warmed up and engine bay hot, try starting and driviing a few minutes without the diagnostic cap on. Apparently, the cap can short out some pins when realy hot. A new cap for $20 will fix the problem.
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