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e30 325is misfire issue

31904 Views 17 Replies 6 Participants Last post by  bizboy
Hello all

I own a 1989 BMW E30 325is with the 5 speed manual. Right about at the start of July it randomly generated a misfire issue. the day before it was running great then overnight it acquired a miss.

I have spent almost the last two months trying to fix this issue all to no avail. Thus far I have replaced the fuel filter, ignition coil, injectors, and I changed out the electric plug coming from the firewall going to the electrical connectors for the fuel injectors with a water tight aftermarket one. On top of all this I have pulled all the spark plugs and tested them to make sure there was a good spark on each one (none of which showed any signs of a miss ie burnt ends) and I have done a compression test coming up with these results:

cylinder 1:170 2:170 3:170 4:170 5:168 6:165 The last thing I will mention here is that I have also checked the codes by turning the key to the ON position and stomping the gas pedal 5 times and watching the check engine light. The car consistently throws up the code 1223 which is supposed to be the coolant temp sensor although the temperature gauge seems to work fine

Some history on the vehicle:
Back at the end of May/early June (1 month before the miss problem started) I replaced the timing belt along with the accessory belts, distributor cap and rotor, spark plugs, and the water pump. After I got everything put back together the car ran fine and I continued to run it for all of June without problems however I should note that there was a consistent overheating issue and loss of coolant. The temp gauge would get to the 3/4 line and stay there unless I cruised at very low rpm's (around 1,000). During this time I also did a oil change as I found the oil level to be low and it was about due anyway.

More recently when I changed the ignition plug going to the electrical connectors for the injectors the miss disappeared however the temp gauge stopped working and my clever dad suggested that I may have got the two electrical connectors at the end of the electrical bar that connect to the coolant temp sensor messed up. Against my will my dad had me switch these two around and what do you know the miss came back and the temp gauge still didn't work! When I switched the electrical connectors around again the miss stayed as well as the temp gauge problem (Later on my dad fixed the temp gauge through unknown means).

Well that's about all the info I can think of to throw in besides that the car has about 170,000 miles on it. I'm out of ideas now and im considering taking it in to a repair shop or a dealership (really hope I don't have to do that though) to have them diagnose the problem so I can fix it. Any help would be greatly appreciated. Thanks again:)
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Crossing the plugs may have 'upset' one of the injectors. The temp sender for the efi is not the same as the one for the dash. If the car has boiled alot then the temp senders (both) are suspect as is the thermostat. Go through the wiring to the injectors again - possibly a pushed back pin or socket or one is electricaly loose. Injectors are often 2v only - unsure about yours.
What do you mean by upset one of the injectors and wouldn't that have been fixed when I replaced all of the injectors which I did last night aka after the plugs were crossed?

Are you saying I should try and replace both sensors and the thermostat?

I triple checked the injectors last night before I installed them and they were all fully seated in the fuel rail with the clips on all the way. I also checked it when I put the injectors in to make sure all were fully seated inside their respective holes as well as making sure all of the electrical connectors were fully seated on the injectors. Does that cover everything you mentioned in the "Go through the wiring" part?

Please elaborate more on the importance of "Injectors are often 2v only -unsure about yours.

thanks for the help I really want to get this problem solved:)
Crossing the plugs may have 'upset' one of the injectors. The temp sender for the efi is not the same as the one for the dash. If the car has boiled alot then the temp senders (both) are suspect as is the thermostat. Go through the wiring to the injectors again - possibly a pushed back pin or socket or one is electricaly loose. Injectors ore often 2v only - unsure about yours.
"Back at the end of May/early June (1 month before the miss problem started) I replaced the timing belt along with the accessory belts, distributor cap and rotor"

I also pulled it apart with my hands after this problem occurred (couldn't take it off because the fan clutch is in the way) but i was able to visually inspect most of it for carbon streaking and the 1/4 or so that I couldn't see I ran my finger along and my finger was clean afterwards so I'm pretty sure that the "Dizzy cap" is fine. nice picture though :rofl:

Oh and all the plugs are firmly in place and in their correct position on the dizzy cap and on the spark plugs
I'm beginning to think that this is a fuel issue because when the car is idling I can not hear a miss and if I slowly increase the revs or hold it at a certain rev there is still no miss. The only time there is a miss is when you are nearly at full throttle to full throttle. I'm guessing then that its going to be a fuel pump issue or a fuel pressure regulator issue. what do you guys think?
If you were to have somebody hold the rev's high while you sniff the exhaust... Does it smell rich? I know my "e" model was having the same issue. I replaced the engine tempature sensor and cleaned the afm, the Idle air control valve and ran some seafoam through the gas tank and cleared it up. Not sure what symptoms of a faulty tps switch is on our cars.. I do know their a common failure though.
re. the temperature gauge not working - my dad advised that he had two of the wires wrong when he replaced the connector(he doesn't remember which specific ones, two of the smaller wires), fixing that cleared that problem - the temperature gauge is working now - and the 1223 code went away after disconnecting and re-connecting the battery cables to reset. The code is now 1444, which is normal. Re. overheating, the car never boiled, but was running a bit hot is all.
The fuel pressure regulator was checked by sniffing the vacuum line going to it for gas fumes - there were some, but no raw fuel - and sucking on the vacuum line to the regulator, there did not appear to be any leaks - the regulator held vacuum. There appears to be ample fuel coming out of the supply hose, strong flow, but not sure what is normal and I have not checked the pressure (no fitting to do that, though I do have a gauge).
Just checked the injectors with it running, using a stethoscope, and all appear to be firing, also cannot detect which cylinder misfires on acceleration. Idle is a bit rough, but it runs up to redline with a gentle throttle no problem and no apparent misfire. Accelerate and it misses, every time, very regular, not sporadic. I am thinking it's fuel - not enough pressure.
you have to add a fitting to check fuel pressure. have you checked the spark plug wires for proper ohms? you could have a cracked wire that when the engine starts to vibrate more could be sending some of the spark to the head.
Hi, Yes replace both temp senders and thermostat. If the engine loom has a plug that allows engine removal without disconnecting each item check that plug too. It sounds like you have a bad track on either the TPS or the air flow meter. Both are fixable for minimal cost, I saw it on another forum. Running up with the car static will not give full air flow or use full throttle. (I'm lucky enough to have access to a chassis dyno so I can run up a loaded motor) I'd go with plug leads too, if they are old. If the injectors have been replaced since the crossed plug then all is well but 12v on a 2v injector will cook it.
Below the intake manifold is a round harness connector which carries the wires for all injectors, and both coolant temp sensors. It is notorious for causing problems. It could be cracked, corroded or both. Give it a good cleaning and see if that helps
I've already replaced that connector with a nicer water tight aftermarket one.
Below the intake manifold is a round harness connector which carries the wires for all injectors, and both coolant temp sensors. It is notorious for causing problems. It could be cracked, corroded or both. Give it a good cleaning and see if that helps
The motronic system is fairly simple. If you are sure that connector is good, the temp sensors are good, next you should test each wire from the ecu end of the harness to the connector end under the hood. Also, get another CPU and swap it in...ECUs do go bad. One last thing,( and this caused a misfire that a struggled with for two race weekends a few years ago), under the driver's side dash, mounted on the firewall to the left of the steering column is a large relay. It is a black box approx. 1"x3"x4", try replacing it.

If you can get your hands on a Benlely Service Manual, use the schematics in the back and do a complete pin out test of your harness, resistance checks on the ecu pins and verify all grounds.

As far as the fuel system is concerned, install an inline mechanical fuel pressure gauge on the feed line before the fuel rail. Knowing that the pressure is good eliminates all fuel components behind rear of the firewall as possible causes. It is also a great tuning device if you have an adjustable FPR.
I've already replaced that connector with a nicer water tight aftermarket one.
Alright. I finally got the misfire problem mostly taken care of (it still misses a little now and then). The problem was that the spark plug spacing was too high. I'm still not out of the woods yet however as the car now has a overheating issue which seems to make the occasional miss worse. Tonight I'm going to replace the thermostat and see if that works. regardless ill be sure to let you all know the progress.
sounds like a bad hg to me.
hg?
sounds like a bad hg to me.
Ah. Yes that is one of the potential causes. The other main one is the radiator
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