86 325e engine swap to 91i idle problem - BMW Forum

lemonhead · 02-16-2006, 07:34 PM

hello to all i have a 1986 325e 5 spd (300k)that ran hot dead/i like the car so i had the engine swapped to a 91 325i motor with total top end rebuild(dme also changed )car ran great for 2 weeks then it started to run rich when at stop lights (would almost bog out)but when i geared it up it ran good.then it basicly got worse so i stopped driving it.tryed to crank it it had a ton of smoke turned it off.now it wont crank just turns over (sometimes if i keep on cranking it the engine will almost fire up but wont)i havent done this much dont want to burn up starter.i have a reset tool with a code reader it shows no bad code.If anyone has any ideas it would greatly appreciated. thanks......

BMWJNKY · 02-16-2006, 10:25 PM

Sounds like a large vacuum leak. I would smoke test the engine to verify if there is a leak and where it is coming from.

Starmavin · 02-16-2006, 10:26 PM

I have been able to make it work by adjusting the A/F raito on the air flow meter with the use of a 5 gas analyzer and the ancient bosch compact test talking to the ecu, but I really don't recomend this, it takes hours and it's touchy as hell, the ecu will fight you every step of the way.

The best way is you'll need to change the computer, air flow sensor, and maybe even wiring harness. The 86 computer is built for the 2.7L, and the 91 is a 2.5 and the 86 ECU can't trim the fuel enough to correctly feed the 2.5 alone.

Even the hollander interchange books says you can take an older motor and put it into a newer car with the note saying "will work, but less power". But nothing on the newer motor working in the older car.

Starmavin · 02-16-2006, 10:28 PM

P.S. You'll get better power by switching the ECU etc. anyway. The 91 2.5 belts out 40 more horeses.

BTW, On the old motronic ECU's in the 86's the MIL codes are lost once you switch the key off.

Aether · 02-17-2006, 01:39 AM

Didn't he say he changed the DME when he swapped engines?
Does sound like a fuel issue.

lemonhead · 02-17-2006, 06:04 AM

Yes i did change DME /and complete wiring harnes/idle controll valve/fuel pressure valve/ox sensor.

Starmavin · 02-17-2006, 06:39 PM

My bad, I guess I missed that. Sorry.
It couldn't be a vacume leak causing very rich condition, that would cause a lean conditon. Well, I'd have to say check your temp sensor also, and your AFM/Air temp sensor, you may also have a faulty fuel pressure reg. Check and see if you have one cyl getting more fuel than the others, could be bad injectors.

Skatebline · 02-18-2006, 02:32 PM

How do u do a smoke test??

Starmavin · 02-19-2006, 02:22 PM

A smoke test is a special machine that works alot like a fog machine. You hook it to the throtle body while it's locked open and it lightly pumps in the "fog" so it'll seep from vacume leaks, making it easy to pin point. Works great, but unless you own a garage, I couldn't justify the cost just to have one for home use.

Skatebline · 02-21-2006, 09:01 AM

Oh, so if i would bring it to a shop and asked them to do a smoke test they would know what im talking about and then maybe do it.

Starmavin · 02-21-2006, 06:05 PM

Quote:

Originally Posted by Skatebline

Oh, so if i would bring it to a shop and asked them to do a smoke test they would know what im talking about and then maybe do it.

Not every shop has that machine, call around before you do.