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1994 BMW 325i starts but then quickly dies. Then just turns over but no start

My 1994 325i has been showing an intermittent pattern of starting then quickly dies. Upon trying to restart the car it just cranks on the battery and will not fire. Within the last few weeks i have changed the plugs, cleaned the air filter, MAF and throttle body. When I cleaned the throttle body I noticed a vacuum hose connected to the intake boot before the throttle body was falling out because the boot was old and cracked. I replaced it and the car started and ran great for about 10 days. Then out of the blue the car wouldn't start when I was leaving work. As a last resort hooked up the jumper cables and...it started right up. The battery is only 4 months old and carries a good charge. When the car is running, it runs great. But the uncertainty of whether it will start or not is concerning.

The first time this happened the car was in my garage and wouldn't start for days...same symptoms. I put the battery charger on and charged to 100%, then the car started. Could it really be the battery? I feel that something else is going on.

Any ideas?
Old 10-30-2010, 05:54 PM
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Check all the earths from the engine to the chassis, make sure they are good, check coil connections too (or do you have individual coil packs)? When it doesn't start, do you have spark and fuel?
Old 11-01-2010, 06:33 AM
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I have a friend that work on BMW's as his day job that thinks that the issue lies between the air filter and the trottle body...the area that I had done work on. His thought is that the vaccuum hoses before the throttle body are still loose. I will recheck them tonight, but you really have to jam the hoses into the new rubber boot before the throttle body, so I don't feel as if these are loose and are the problem. Is there something within in the chain of air filter to throttle body that would prevent the car from starting up? I am pretty careful to put everything back together correctly and tightly.
Old 11-01-2010, 01:55 PM
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Not entirely sure of the 1994 set up, but you should re check the MAF and sensor in that line, and the electrical connection to it. there could be a vacuum hose under the throttle body itself that was disturbed.

Also sounds like a new battery will help the problem?

Check the battery earth connection to the chasis.....maybe with both batterys connected you are getting full 13-14v and amps, with one, there could be some losses due to poor earth?
Old 11-02-2010, 05:35 AM
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I disassembled the MAF to get back to the U-shaped rubber boot that connects to the trottle body. I then pulled out the two vaccuum hoses to that connect to the boot. I checked the boot (just bought it to replace the old cracked one) to see if the port holes were blocked or were cut too small. The boot looked good to me. I then traced the two vaccuum hoses to see if the other end of the connection was loose. They did not appear to be. I did notice that the one hose that connects to a port that is on the front of the engine near the top (in an area that recently had a new value gasket put on) had some oily build up. I giggled it to make sure it was resonably tight. I then reattached the boot to the trottle body, put the vaccuum hoses back in the boot's appropriate holes and then reconnected the MAF and tighted with the circle clamps. I then was able to start the car. I turned if off, let it sit for a while then started it again. I did this a few times and each time the car started and idles and runs great.

The car worked fine before too, and then out of the blue (usually at the worst times) goes into this pattern of not starting. Its running now, but I am worried that I will drive it somewhere and then later, it will not start. My road to work is quite bumpy, are the vaccuum hoses that sensitive that a bumpy road will disrupt something? Could one of the hoses been screwed into the boot too far?

Last edited by The Green Ghost; 11-02-2010 at 06:57 AM.. Reason: misspelling
Old 11-02-2010, 06:54 AM
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If you have a HUGE air leak then its possible to create the instant non starting issue, a slight leak is more likely to cause a poor idle, acceleration and fuel consumption.

Have you done a compression test on the engine since you have had it.....if nothing else it will tell you the approximate condition......you shoudl be getting 160-170 psi from a reasonably good engine across all cylinders.

Forgot to check if you have done changed the spark plugs, HT leads, distributor cap and rotor arm yet? Use copper core plugs as they seem to work well in these engines.
Old 11-03-2010, 05:21 AM
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Frustrated again...yesterday I was able to start the car, drove it around before I went to bed and even was able to start it in the morning to let it run for 10 minutes. When I got home from work I went to start it again and the same thing is going on. The car cranks, then breifely starts , sputters quickly then dies. Attempting to restart it only results in contineous turning over. I had the battery fully charged, so I think I can rule this out. I don't think it is a leak in any hoses that connect to the trottle body as the car had started and idled fine 8 hours earlier. What can make the car start up, and run and drive just fine then after it sits for a few hours - it won't start?

Other things I am noticing are that upon tring to start the car numerous times with no success, I build up a lot of back pressure in the coolant overflow tank and have to release the air pressure by twisting the release screw. I also have seen a considerable drop in the coolant level, but it is not leaking out under the car or anywhere else that I can see. I have checked for the common symptoms for a head gasket problem and don't see them.

I also hear a buzzing sound from what I believe is the idle control motor under the intake when the key is turned to the start position before starting. The buzzing is also sending vibrations to the hoses that connect to the throttle body. Is this normal?

I tried to perform the stomp test to get some code read outs if there were any, but am unsuccessful to getting it to work. I have the bently repair manual for this car, but I only know how to do a certian amount of tests.

If I turn the key to the on position, should I be able to walk back to the gas tank and hear the fuel pump motor working?

I can't seem to solve this problem and appreciate any suggestions.
Old 11-03-2010, 08:08 AM
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Hmm not sure if the coolant symptoms are related or not.......if a worse case, a failed head gasket or cylinder head will allow the coolant and oil systems to cross over....is there any sign of oil in your coolant, or whitish emulsion build up?

Have you checked for fuel being delivered during cranking......a fuel pump failure or poor performance can cause bad starting......

If you do think the coolant issue shows a head problem, get a compression tester and check what pressure each cylinder is giving....they should all be reasonably the same and on an E30 325is its about 170 psi?
Old 11-04-2010, 05:16 AM
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Last night I detached the MAF, and disconnected the electrical component. Then I also detached the C shaped air flow boot that connects to the trottle body. Lastly, I pulled out the two hoses that connect to the air boot. While this was disassembled, I looked around for anything else that might be loose or not connected right - everything looks fine. I then re-assembled everything and went to start the car, and it started and idled just fine. THe weird thing is that this is exactly what I have done 2 times before (disassembling and reassembling) and both times the car started and ran great. The problem has been, about 8 hours after the car has been sitting, I get in to start it, and it quickly fires up but then dies. Trying to start it after only results in continuous cranking. What can be happening were simply by taking these peices off and putting them all back together can make the car start; and why some time later after the car has been sitting it then won't start?

Also - I still have a ton of back pressure in the radiator overflow tank. I released the air and added some coolant then started the car for 5 minutes. Even after 5 minutes the tank had build up a ton a pressure and coolant would spit out while twisting the release screw. Any thougths here?
Old 11-04-2010, 06:53 AM
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Does the car run when you depress the accelerator pedal?

If so, the idle air control valve may need cleaning.

The pressure concerns me though, do you have oil in your coolant?
A compression test may be in order. Has the car been overheated to you knowlege? You should have an M50TU engine so there is no distributor or rotor, so don't look for it, but you do have a crankshaft position sensor that can cause these type of problems. Also, the 02 sensor is a very likely culpret. The engines ECM needs input from these sensors, or it may not run run at all. Most other sensors, such as MAFF, intake air, and coolant temp will send it into a default, or "limp home mode" . The throttle position sensor is also one to look at. Most sensors can be checked with a good digital OHM meter. Have you downloaded the fault codes? That may help you sme, although a 94 is like my 93, the codes are old technology, hit and miss sometimes.
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74 911 targa blk on blk, Carrera fend., tires & whls. gone, missed
85 325e bought new, totaled after 20 years & 465K miles, trouble free service.
01 Ford Ranger 4dr stpsd 4wd. I drive,here
88 325i convert. only 98k miles,gone, sold
93 325i.here, 98 Z-3 roadster. gone, 08 128 cabro gone
Old 11-06-2010, 10:09 PM
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I had my mechanic friend run a diagnostic test on the car. The print out indicated that the Knock Sensor #1 was out. I had replaced the Knock Sensor #2 no more than 2 months ago. That was the only code that was produced. The coolant reserve tank still builds lots of pressure, to the extend that if you do not twist the release screw to release the air, coolant will seep out of the cap when you are loosening it. Obviously, this is concerning to me, but also the coolant that comes out is a watered down reddish color, when I am putting in a green colored coolant. I am worried that there is some oil mixing in with it, thus there may be the start of a crack in the head gasket. I don't see any of the other tell tale signs of a head problem though. There may be a little back-firing while idling though, which I thought was originally just the result of new plugs, valve gasket cover and the performance dinan exhaust system.

Lately, the car has been starting up, idling fine and acutally running fine too. I read in a prior thread that a head problem may have a symptom of when running the heater, that it will go from hot to cold and then back to hot. Mine is doing this. I had the thermostate looked at and it is ok.
Old 11-09-2010, 06:44 AM
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The coolant system shoudl build pressure, its the pressure in that system that stop water from boiling at 100 degrees C and raises it to something higher (I can't remember what now). So as long as you have vented all the air out of the system and topped it up, the pump should circulate the system and purge any small air pockets into the header tank.

Did you flush the coolant system well before re-filling? The reddish colour could be a rust build up in the radiator and general system.

Signs of a head gasket can include, loss of coolant with no visable leaks, steam or white smoke coming from the exhaust tips, severe pressure in the header tank and of course high temperature, and oil emulsion, usually white or creamy coloured on top of the coolant in the header, or aroudn the filler cap and even on the dip stick.

If you mechanic was able to diagnose the knock sensor, he will be able to do a compression test very quickly (about 20 mins) or you could invest in a gauge and do it yourself in say an hour. This will tell you if you are getting any pressure loss between cylinders or into the cooland jacket etc.

Have you checked your timing? backfire?

Is it running on all 6 cylinders smoothly enough when it does run?
Old 11-10-2010, 05:06 AM
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I have not checked the timing. How is this performed? Can I do it myself or is it done by a mechanic?

I am noticing a drop in coolant level with no visable leaks, only after running the car for a short time. I know there is supposed to be pressure in the reserve tank but mine seems exessive. The idle waives a little bit too know; but that could be due to the idle control valve. It also could be due to buring some coolant in the cylinders?
Old 11-10-2010, 06:45 AM
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Compression test
Old 11-10-2010, 11:40 AM
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I agree, do acompression test, while you have the plugs out, inspect them. Make sure you note the condition in cylinder order and reference it to the results of the compression test, because if you have a suspect plug along with low compression, you need to go the next step.

If your compression is the same on all cylinders (+/- around 10%), and you don't have any indication of fouled plugs, and no white or milky oil, then you most likely don't have a blown head gasket.

Pressure in the cooling system is normal as long as the components are correct. Excessive pressure would be vented by the system in the form of vapor or steam and you would hear it or at least smell it.
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74 911 targa blk on blk, Carrera fend., tires & whls. gone, missed
85 325e bought new, totaled after 20 years & 465K miles, trouble free service.
01 Ford Ranger 4dr stpsd 4wd. I drive,here
88 325i convert. only 98k miles,gone, sold
93 325i.here, 98 Z-3 roadster. gone, 08 128 cabro gone
Old 11-15-2010, 05:17 PM
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Thanks for all the feedback and ideas. I will be checking compression.
Old 11-19-2010, 01:35 PM
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Old 11-19-2010, 01:35 PM
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