Looks like the engine swap from the '81 parts car I bought is bad. Low compression (around 100) on two cylinders. The car also drives like it has a rev-limiter set at 3300 RPM. I have been through a long list: valves set, timing set and reset, AFM, throttle body, vacuum, injectors, etc. The last thing I thought I would try was to swap the head with one I have on hand that was rebuilt at one point (condition appears good but used). Not sure if I want to go through it or just sell the car.
Questions: 1 - why would bad valves (oil in the cylinder does not raise the compression) act to limit revs? 2 - Anyone think the head swap will be worth it? I am very close to selling this car as is. Thanks in advance for any info.
Final Throes -- Head Replace or Not?
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BradInTexas
- Posts: 40
- Joined: Tue Jan 06, 2009 10:25 am
- Location: Weatherford, Texas
Swapping the head won't fix it. Now if you had two dead cylinders, it could be a problem, but just low wouldn't cause a rev-limited like problem. It might run a little better, but you're not going to have a great big difference. How is power up until it hits the wall? Very good, or a slug or what? If it's just fine until it hits the wall, I'd guess ignition control unit or maybe even the ECU. But I strongly suspect it's electronic/electric one way or another, not mechanical. Compression readings have surprisingly little affect on performance.
You know, one more dumb question, are all the spark plug wires on in the right places? I know, I know, I'm sure you've checked, but if it's not right at any speed, check on it too.
You know, one more dumb question, are all the spark plug wires on in the right places? I know, I know, I'm sure you've checked, but if it's not right at any speed, check on it too.
Mike W.
1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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BradInTexas
- Posts: 40
- Joined: Tue Jan 06, 2009 10:25 am
- Location: Weatherford, Texas
It does seem electrical or timing related
I just haven't been able to put my finger on it. I'll go back through everything this weekend. I have spares of everything from the donor car (ICU, resistors, AFM, distributor), and have swapped everything but the resistors, ICU and distributor, so maybe I will go that direction. I kinda figured that even with the low compression I could get it to run smooth. I really appreciate the input. Thanks.