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Need help with m42 swap issue

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Calling everyone who has experience with m42's (e30) version  my m42 swapped 02  does not want to idle when the engine is cold , i hooked  up my bmw scan tool  and the engine temp non running is room temp then when i checked again , it said 194 c when room temp was 65f or 20c  . the only error codes i have gotten when i pull them are ID =3  fuel injectors 1+3 ,100 output stage  and id 1 electric fuel pump relay EKP., i have replaced all 4 fuel injectors , i have replaced the vacum line running to the fuel pressure regulator , i have replace the fpr . i have done all the gaskets on the intake and exhaust and the valve cover , tried swapping the 02 sensor droped the idling rpm once warm to 600 rpm no change on cold start up .  I had the afm rebuilt  , and put a  new icm  in , changed nothing the only things i have  not changed are the oil pressure sensor , engine temp sensor ,  cranks and cam shaft sensor .  and the  down pipe to the header the connection leaks there a little bit confirmed via smoke test .  Any ideas on what could be wrong ?


Any advice would be greatly appreciated.


Thank you so much.

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I'm assuming it was running fine with no changes else I'd suggest that the connections on the two sensors on the head under the intake are swapped. What circumstances occured before it started running poorly when cold? Anything definite or ?


Not to throw more parts at it but the engine temp sensor may be flaky (194c vs. 20c), so thats a consideration.


Keep looking for vacuum leaks - I'm assuming the "mess under the intake" has been simplified. 


I'll keep thinking. Also check in at r3v. https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m42




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 and the engine temp non running is room temp then when i checked again , it said 194 c when room temp was 65f or 20c  .


Do you mean that it's 194 f while it's running?


Because if it's reading 194c at any point, you're not getting a good engine temperature signal, and that will certainly

cause trouble with idle.  It's not a bad idea to meter the sender- you're looking at the voltage-

and see if it's stable as the car starts and warms up. Grounding can mess with this, too, so if you're dedicated, 

meter the sender end AND the pins where they enter the DME.


It's harder with the earlier DMEs- they just aren't as 

chatty as the OBD2 versions, and the data they provide

is often not interpreted correctly by more recent readers.


This was a tough time for engine diagnostics- mechanics are hard to train, and in the mid-90's,

no- one wanted to have electronics stuffed down their throat.  BMW didn't do anyone any favors

in the long term, either, with their closed- shop mentality, and third party

electronics.  It seemed so cool and high- tech at the time, but instead of tapping

a then- interested market, they effectively alienated it and to a large extent, killed it off.

So here we are with a dwindling enthusiast market and

little support for the part of it that likes to take things apart.

"Nobody will fix my car for me!"



end- stage predatory capitalism

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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Could this be just a really ( crap) battery causing this . the car will turn over fine . but lack of volts could mess with things . ill put a volt meter to the battery later this week and report back ( im going to be pissed if that was it) 

Edited by M4202
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yes- sort that temp sender. 

The M42's DME is easily confused.

Me, I'd measure the voltage on the DME sense pin.

And +1 for stable voltage at the battery, too.



http://www.wedophones.com/Manuals/BMW/1992 BMW 318ic Electrical Troubleshooting Manual.pdf




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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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