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Discussion Starter #1 (Edited)
Hi all,

I´m new at this forum. Recently, I bought 1992 M5 3.8i in bad shape. First thing whitch bothers me is rough run of the engine.

I have low idle (arrond 750), rich mixture (my sparkplugs are totaly black) and I can feel and hear misfirings up to 4000rpms.

I changed sparkplugs, water temp sensor, change some rubber tubes, checked vaccum lines, do engine cylinder compression test (compresion is from 13.5 to 14.5bar), change O2 sensor, checked coil packs, clean air valve.

I´m also searching for air leaks but I can not found any.

I have also deleted air pump but I still not remove the tube which goes to exhaust manifold. There is also some vacuum line leading to air pump. Should I block this vacuum line?

A have read many topics at this forum but nothing is helping to make my engine run smooth.

Can you give me some other advice?

Thanks

Martin from Czech Republic
 

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What is the P/N of the fuel injectors? Did you test em?
 

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I don't remember actually but i think so. But watch out, with the low idle maybe the result could be confusing.
 

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Discussion Starter #7
Can low or high pressure cause low idle? I will messure pressure in some ranges of rpms and see what will be the results.
 

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Discussion Starter #11
I dont hove new air filter but I checked it and it looks normal. Do you realy think that air filter can cause this problems?
 

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If it's blocked, that's exactly what would happen. You're looking for too much fuel, or not enough air.

For me... Air Filter, O2 sensor, MAF are the key candidates if the engine is otherwise healthy.
 

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Discussion Starter #13
If it's blocked, that's exactly what would happen. You're looking for too much fuel, or not enough air.

For me... Air Filter, O2 sensor, MAF are the key candidates if the engine is otherwise healthy.

O2 sensor is new. I have already ordered new filter. I will let yo know if there will be some change.

Thanks for advice
 

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Discussion Starter #14
If it's blocked, that's exactly what would happen. You're looking for too much fuel, or not enough air.

For me... Air Filter, O2 sensor, MAF are the key candidates if the engine is otherwise healthy.

O2 sensor is new. I have already ordered new filter. I will let yo know if there will be some change.

Thanks for advice
 

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For 3.8 L I think is 3.5 BAR and for 3.6L is 3.0 BAR

Did you adjust the MAF screw? Did you clean it anytime?? There is a special spray cleaner for the MAF.
 

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Discussion Starter #16
For 3.8 L I think is 3.5 BAR and for 3.6L is 3.0 BAR

Did you adjust the MAF screw? Did you clean it anytime?? There is a special spray cleaner for the MAF.
No I didn´t do anything. I read about the screw but I didn´t find any information how to adjust this screw. What does it influence?
 

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No I didn´t do anything. I read about the screw but I didn´t find any information how to adjust this screw. What does it influence?
It does adjust the fuel mixture at idle and I think it does adjust a bit under light throttle as well (kinda like open loop). Mine is modified (MAF) and has another screw that I had to adjust it to get correct 14.7 AFR at idle in my case and good throttle response, although I have provisional wide band gauge in my car to monitor this and the whole behavior of the engine under different loads.

Take a look at the injectors part number, it's not that difficult and report back.
 

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Discussion Starter #18
So, I got new air filter, but there is no change.

Injectors P/N is 1317446.



Can somebody tell me what is part 17. I don´t have this in my car. Is it necessary to have it? It is described as pressure tank.

Thanks
 

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I can't see the picture on my device, but if it is on the air filter page I don't have one either.

What happens if you unplug the MAF? The car should run from a predefined map, so this might help rule that out.
 
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