Motor down on power, what am i missing?


Hello everyone, I have an 89 325i that is way down on power. The car dynos about 10hp under stock all the way up to 6k rpm and then drops another 25hp to redline. We have changed injector, AFM, plug wires, coil, and run a leak down and compression check. The motor sound strong and pulls clean, but doesnt make power.


Double check the ECU…it is a 25+ year old car with multiple owners along the way.



What were the results of the leak down and compression check?

Might want to post the dyno chart. “10 under stock” is kinda ambiguous.

Dyno runs for troubleshooting purposes really need F/A info in the results. By chance did the put a wide band O2 sensor in your tailpipe when the did the runs?


[attachment:1]C:\fakepath\e30 dyno results.JPG[/attachment]


Sorry, cant get my dyno results to download, but here are the numbers…
3000 - 65hp / 118tq
3500 - 75 / 118
4000 - 100 / 130
4500 - 120 / 140
5000 - 130 / 137
5500 - 143 / 132
6000 - 128 / 120
6300 - 120 / 100


Looks like you have the 318 engine. :stuck_out_tongue:
Do you have the air/fuel numbers?


At this point I might take a strong running 4 banger over this boat anchor LOL. AFM was between 12.5 and 13.8.


you need compression and leak down tests.


Compression is 150 - 155 across the board


The one thing we have changed is the DME, primarly because we cant find one anywhere. Is there anyway to test one beyond swapping it and driving it?


Were you on a dynojet? They say that dynojets are around 10% high. Better dynos can give you both real HP and “Dynojet HP.”


Yes, dynojet


Isn’t Dynojet the spec dyno? If Dynojets are known to run “10% high”, does that mean our cars are putting out more like 140-145hp?

Really don’t want to turn this into a rules argument about the hp, just curious because I had my car dyno’d on a Dynojet at Thunderhill. I didn’t ask them about having it “corrected to SAE J1349 Rev JUN90” per the spec, though. (not sure if that’s default behavior anyway) Came up with 145hp on my 200k motor with 13-14 AFM, which is what prompted me to accelerate my head rebuilding timeline (and air flow meter slider adjustment, and injector cleaning, and TB cable adjustment).

Curious if I’m supposed to expect that I was really running less than 145.



Jim Levie has a good troubleshooting guide that includes ECU tests, but I doubt that would show anything in your case since it seems to be running well. Swapping is a pretty easy troubleshooting technique in this case, and not terribly expensive. Search eBay for “0261200173” and you should find a few. I bought two within the past couple weeks for $65-70 each, with free shipping. Haven’t been to the dyno, but both work well enough for the car to start, which is an improvement over the original.



[quote=“Bahnstormer” post=80964]Sorry, cant get my dyno results to download, but here are the numbers…
3000 - 65hp / 118tq
3500 - 75 / 118
4000 - 100 / 130
4500 - 120 / 140
5000 - 130 / 137
5500 - 143 / 132
6000 - 128 / 120
6300 - 120 / 100[/quote]
The way to get really good info is to get the raw data, download DynoPep or whatever the graphing app is, and then fool with the graph until you can zoom in on 4000-6400rpm, and 12.5 to 14.5 F/A. By zooming like that you see a lot of detail that you’d otherwise miss. The F/A that you reported seems pretty good, but we’re still hamstrung in that we can’t see the real dyno plot that has so much more info in it.

Based on your compression test #'s the engine may well be mechanically ok. It would be nice to see your leakdown #'s too tho. Ideally, you could discuss your compression #'s and your leakdown #'s in the context of what the tester normally sees. For example, I always get lower #'s then most other people for some reason I’ve never figured out. So it would be helpful if the compression and leakdown tester dude added some editorial comments re. the results of his tests.

If your F/A really is ok, that rules out a lot of things. Or at least it makes it hard to assert most theories that come easily to mind. Fuel pressure and injectors pretty much have to be ok if F/A is ok. Ditto for AFM. You might check Throttle position sensor, but a bad TPS wouldn’t explain the behavior.


How many miles are on your engine? I have an 89 as well, with 188k on it. Your dyno #s are almost exactly the same as my last dyno (146hp/137tq). My engine runs well also, its just not so eager to get up to speed. Previous owner replaced the same parts as you also.
Im hoping a head refresh will bring me up to speed.


check your timing, if the belt is off by one tooth that would cause this.


Good idea Andrew


Checked the timing and its spot on. We did located a DME last night so we are headed to TWS for a WRL event, hopefully that fixes it, if not Im praying for rain :slight_smile:


Yes the dynojet #s are the ones that matter to us. I was just saying that if you were using a different dyno that you may not even be down on power at all.

Last year I found 7HP. The two things I did were replacing the “good” AFM with a new reman unit, and toss my K&N in the trash for an anything but fram.

Eric, you’ve got enough power already.