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Tidy30

E30 Starting issues - feat. brand new clue today

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Hello friends,

I have been having some starting issues with my E30 for the last little while. Here are the following symptoms, and a little update at the end from today which might narrow things down. Please have a look below and let me know what you think it might be:

  • Engine needs to crank for like 5+ seconds with my foot 30% on the accelerator before it is able to start
  • Only marginally better when the engine is warm
  • A whole bunch of very fuelly smoke comes out from the exhaust when it starts (exhaust smoke looks and smells "regular" after driving a while though)
  • Engine can sputter slightly for maybe 1-2 seconds when gently accelerating from stand still
  • When moving slowly in crawling traffic, sometimes can hear motor revs slightly modulating/pulsing, going up and down
  • Rough idle
  • When 3-point-turning into parking spot, during the 2nd turn when the car changes direction from fwd/back with low revs, very rarely the engine can die/stall out 
  • Fuel economy is pretty poor. Went very roughly 400km on a 60L tank of fuel, so around 15L/100km. I haven't driven my E30 in a long while but I remember 10-12L/100km as a ballpark economy figure

 

Now for the potentially informative clue today:

  • I had a feeling my issues are fuel related, so I swapped out my fuel filter this afternoon as it was long overdue.
  • Following a youtube guide, I took out the fuel pump relay and started the car. Without the pump the car quickly clears out the fuel in the line so I'm not drenched when I take off the old filter.
  • After taking the old one out (and getting slightly drenched in the residual fuel) and putting the new one in, the lines are obviously very empty of fuel prior to starting the engine.
  • Turning the key and expecting another 5+ second beating before it starts, I was ecstatic when the engine started 2nd crank! No staring issues at all! I ran it for about 10 seconds and switched it off. 
  • Attempt number 2 was also very smooth and successful!
  • I drove to the petrol station with the hugest grin, beaming!! My long term problem was finally fixed!!
  • However, after a 5min drive and a refuel, the engine was back to it's old 5+ crank battle from before. Same with the slight sputter when gently accelerating.

 

TLDR and my amateur thoughts:

  • Something is causing my car to inject waaaayy too much fuel when starting? (Potentially just all the time). Car struggles to start for ages and when it finally does there is a big cloud of fuelly smoke. When I emptied the fuel lines today the car started no problem. But after driving around perhaps the lines are filled again and the car gets too much fuel again to start easily?

Does this sound like something you know? Would greatly appreciate any hints and tips. My precious E30 has been a bit of a concern for a while, and now I'm commuting again it's something I'd like to iron out asap.

 

Cheers in advance for the help guys! 😄

 

Edit:

My car also had this weird additional hose sticking out into the air. I'm pointing at it on the right. The photos are looking up into the bottom of the car. This hose wasn't in the E30 video I watched. But I read somewhere the larger fuel tanks have an additional line or something?

 

20210412_170641.jpg

Edited by Tidy30

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Checked the usual? Vacuum leaks, intake leaks, dirty MAF, ignition system

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I can't see the pic - Google images sucks for that.

If the engine temp sensor is reporting the engine as cold, it'll inject extra fuel.

The temp gauge and the ECU have different signals, so they don't see the same values. I can't remember if the late E30's use one sensor with 2 outputs, or if it's 2 sensors though? Certainly worth checking. I'm assuming the gauge is reading straight up and down at "normal" temp after running a while.

 

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I have the blue coolant temp sensor and the brown gauge sensor. You might be onto something, I unplugged both sensors and jiggled the wires around the other morning and the car started first pop! But then went straight back to the same issues.  Need to try again to confirm if this is really a thing...

I recall getting new blue sensors in the recent past, so it might be wiring related. Not too sure what an easy way to diagnose that would be...

 

Edit: can anyone point me to what the readings should be on the ECU plug? I will take it off this weekend and have a go at reading the values reaching the ECU. This should help with the MAF too

Edited by Tidy30

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Any update on this? 

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On 4/12/2021 at 9:50 PM, Tidy30 said:

I have been having some starting issues with my E30 for the last little while. Here are the following symptoms, and a little update at the end from today which might narrow things down. Please have a look below and let me know what you think it might be:

Let me start by saying I know nothing about E30's, but I have messed around with old cars. So assuming that your E30 has a basic port injected engine with a separate cold start injector, I would guess that your cold start injector is stuck in the ON position. This will cause over fueling on start, a rich mixture (particularly at low rpm) rough idle and poor fuel economy. If this assumption is correct, disconnect the fuel connection (or clamp the hose) to the cold start injector and see if there is any improvement. The cold start injector should likely only get 12V while the engine is cranking, so you could also check to see if by any chance it is getting a constant 12V when the ignition is ON.

One other possibility...  if the E30 happens to have a MAP sensor for engine load instead of an airflow sensor, check that the hose to the MAP sensor has not split or become dislodged.

Cheers...

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On 4/16/2021 at 6:37 AM, KwS said:

yup comon issue for these tio fail , go open circuit causes fuel mixture to go pig rich 

also the cold start injector thermo timer switch can go bad 

also AFM resistance scale can go high resistance 

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