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Reviving 81 528, runs, but no power, Any ideas?
Posted: Sat Aug 01, 2026 11:42 am
by SP250rich
Hi folks, I have a 81 528i manual, CA car (Completely stock) that ran great a year ago. It was reclaimed with the help of 2 other 528i donors and G-son's help. Now with next G-son, and here is the problem for you "detectives". It starts, runs and idles smoothly, but not much power. When we drive off, it has about 20% of normal power, but still runs smoothly. Data: Timing set to spec (mark at 2200 rpm), good compression (160, 159, 154, 160, 157, 142), good fuel rail press (31 to 39 psi), new fuel filter. Eng vacuum (idle =15 inHg), but goes to zero with full throttle (and very little power up a hill) Free revs to 4500 and still smooth. Cat replaced 3 yrs ago; muffler stock. Running out of ideas. Help!!
Rich in Moraga, CA. Near San Francisco
Re: Reviving 81 528, runs, but no power, Any ideas?
Posted: Mon Aug 03, 2026 2:09 am
by tlake
SP250rich wrote: Sat Aug 01, 2026 11:42 am
Hi folks, I have a 81 528i manual, CA car (Completely stock) that ran great a year ago. It was reclaimed with the help of 2 other 528i donors and G-son's help. Now with next G-son, and here is the problem for you "detectives". It starts, runs and idles smoothly, but not much power. When we drive off, it has about 20% of normal power, but still runs smoothly. Data: Timing set to spec (mark at 2200 rpm), good compression (160, 159, 154, 160, 157, 142), good fuel rail press (31 to 39 psi), new fuel filter. Eng vacuum (idle =15 inHg), but goes to zero with full throttle (and very little power up a hill) Free revs to 4500 and still smooth. Cat replaced 3 yrs ago; muffler stock. Running out of ideas. Help!!
Rich in Moraga, CA. Near San Francisco
Perhaps the AFM flap (vanemeter) is sticky
Re: Reviving 81 528, runs, but no power, Any ideas?
Posted: Mon Aug 03, 2026 10:43 am
by Mike W.
Could be the cat. They can plug up and get restricted causing a lack of power.
Re: Reviving 81 528, runs, but no power, Any ideas?
Posted: Tue Aug 04, 2026 3:27 pm
by SP250rich
Thanks for the hints, so far.
Have checked the AFM. Flap moves smoothly. Smooth/even driving response, just no power.
Cat. Is there a way to check this? What should the back pressure be? Assuming I can use the O2 sensor port to add a pressure gauge. Or is there a simpler approach?
Rich
Re: Reviving 81 528, runs, but no power, Any ideas?
Posted: Sat Aug 08, 2026 11:21 am
by Mike W.
Actually just removing the O2 sensor is supposed to bring a noticeable improvement. When mine was plugged, it was restricted with low power, but fully driveable, I could even tow my little trailer, so it was hard to get a conclusive back pressure reading. Search the 'net, there's plenty on it.