1991 325i m20 help, madison

cpandrewschmidt

Hi all,

Any m20 engine experts or just people good at diagnosing engine sputtering issues on older bmw around the madison area? I recently bought a 1991 325i convertible. Did all the major tune up items, plugs wires distributor, timing belt, etc. The car is still sputtering a bit and I'm not sure what to try next. Wondering if anyone would be up for some beers on me if they could help me figure it out? Thanks much

Andrew

straight6pwr

From experience I'd look for vacuum leaks, fuel delivery issues (pump, filter, regulator), and then various sensors and controllers last (coolant temp, afm, o2, ecu, etc)

Someone with the right tools can diagnose fuel/air issues pretty quickly, which I recommend over throwing parts at it.

jc43089

Do the issues happen all of the time? Or only when cold or hot? Is the tach steady or does it dip occasionally? That can indicate a bad crankshaft posistion sensor. I had a marginal cps on my vert and it would hiccup every few minutes or sometimes run fine for days. A vacuum gauge is helpful, I have one you can have. Pm me your address.

Sent from my potato phone

cpandrewschmidt

Thanks, the tach does dip occasionally. it's pretty frequent when it does it. Most noticeable during acceleration and deceleration. When at cruising speed it isn't as bad, but still prevalent.

i didn't seem to notice issues until i changed the plugs and wires. I went with BavAuto's high performance wire, and bosch plugs. But i can't say for sure there weren't issues before as the car was sitting most of the winter. I only drove it from IL to madison and then started working on it. On that trip it was never this bad. All items replaced:

timing belt, timing belt tensioner, all belts, distributor cap, water pump, thermostat, valve cover gasket, plugs, wires, air filter. All the tune-up things since i didn't know when they were last done. Car definitely ran better before performing these things which is strange.

I'm wondering if the high performance wires might have something to do with it. Plugs and wires were the last things i did. I drove it before doing those and i didn't notice this issue this bad. Unfortunately i pitched the old plugs and wires so I can't test if that might have something to do with it.

I'll read up on vaccum testing. Other suggestions welcome! Andrew

andyhundley

Do you have the timing set correctly?

jc43089

I have had poor experiences with Bosch plugs, the 4 ground ones. I prefer NGK standard ones, which are actually OE on certain engines.

Sent from my potato phone

YoungCR

These engines can be finicky on plugs, everyone seems to prefer the NGK but it also depends on the type of plug.

I'm basically doing the same thing as you, throwing parts at the 325i because its that time anyways. I would be willing to swap around parts if you wanted to meet at my shop sometime. I'll keep what I take off the car this weekend in case I run into similar issues but I don't think mine could run any worse

jc43089

The plug issue was on my m50 and I had a noticeable power and mpg improvement when I switched to the NGK. I didn't realize at the time that NGK was OE and just used them from previous good experiences. I found a set in an m52 with 210k on it that had NGK on one side and BMW on the other side of the spark plug.

The vacuum gauge can be helpful to diagnose leaks, spark issues, a sticking valve. Somewhat more application on even older engines where you could adjust the timing by turning the distributor, old mechanics can set the timing with a vacuum gauge. The one I am sending is a cheap one and reads a little low but the main thing is how the needle moves rather than the actual measurements. I took a couple videos that I will post later.

The dropping tach needle could be a CPS issue. I noticed that when driving with the cruise on it would feel like a misfire when the needle dropped. The CPS tells the ecu where the crankshaft is so it knows when to send the spark. If the CPS isn't pulsing you won't get spark at all. Here are some pics from mine. http://www.wibimmers.com/board/index.php?/topic/2215-new-ride-89-e30-vert/page-6

cpandrewschmidt

CYoung said:

These engines can be finicky on plugs, everyone seems to prefer the NGK but it also depends on the type of plug.

I'm basically doing the same thing as you, throwing parts at the 325i because its that time anyways. I would be willing to swap around parts if you wanted to meet at my shop sometime. I'll keep what I take off the car this weekend in case I run into similar issues but I don't think mine could run any worse

thanks cyoung. yeah id love to swap plugs / wires to start there and see if thats the issue before getting to more expensive things. visversa if i have some parts you need to try. where's your shop?

JC43098 - i could have what you're describing. i'll try to drive and post a video of whats happening

i think i have the timing ok after the change? i hand cranked everything a few times through and it all lined up as it was supposed to.

Andrew

Jdesign

cpandrewschmidt said:

All items replaced:

timing belt, timing belt tensioner, all belts, distributor cap, water pump, thermostat, valve cover gasket, plugs, wires, air filter. All the tune-up things since i didn't know when they were last done.

I would look at the fuel filter and fuel pump if you haven't yet. I am in Cottage Grove and am more than willing to help you diagnose the problem. I am around almost every night after 5pm.

cpandrewschmidt

Thanks Jd, I'll probably take you up on that. I haven't had a chance to get it out again and the weather didn't help last night! I'm also waiting on my plates to arrive, so I don't want to drive it on the street too often. After I can get it out I'll shoot you a PM.

JC - I got your vacuum gauge. Can you help me figure out how to use it by any chance? Never done a vacuum test before.

Thanks again,

Andrew

jc43089

Easiest place to attach it is to unhook the fuel pressure regulator and hook the T inline there so the vac gauge and fpr are hooked up. Then run the engine and observe. That gauge reads low so a good reading would be around 17-18 and steady.

cpandrewschmidt

did the vacuum test, at idle it was at about 11ish PSI. Pushing the gas in neutral it would jump up to 17-18. All lines and hoses seem seem intact. Anyone ever try the cigar smoke test on these cars? Where would i introduce the smoke into the system?

Changing fuel filter tomorrow. Cleaned ICV

Every time i start the car it seems to get worse. I'm stumped as problems only arose after doing routine maintenance and I haven't driven the car more than 20 miles from swapping parts. I don't think I will make it to anyone's shop who's offered to help me (thanks again by the way you guys!) without breaking down as bad as its running. Don't suppose anyone is around the westside that could help for a beer?

Andrew

B C

I made a smoke tester that connects to the brake booster line, you just put a bag over the intake to keep smoke from escaping from the filter.

I wish you were closer and that i had time to assist

jc43089

cpandrewschmidt said:

did the vacuum test, at idle it was at about 11ish PSI. Pushing the gas in neutral it would jump up to 17-18. All lines and hoses seem seem intact. Anyone ever try the cigar smoke test on these cars? Where would i introduce the smoke into the system?

Changing fuel filter tomorrow. Cleaned ICV

Every time i start the car it seems to get worse. I'm stumped as problems only arose after doing routine maintenance and I haven't driven the car more than 20 miles from swapping parts. I don't think I will make it to anyone's shop who's offered to help me (thanks again by the way you guys!) without breaking down as bad as its running. Don't suppose anyone is around the westside that could help for a beer?

Andrew

The idle vacuum is too low. Is it steady, fluttering, or wandering? That is an ok reading when at higher RPM on that particular gauge, 17-18 is actually around 21-22 inHg. (inches of mercury, a smaller measure of pressure).

You are sure the cam timing lined up right? You should try removing each spark plug wire one at a time and see if there is one that does not make a difference. There could be a bad wire even though they are new. You will see the result immediately if the cylinder was working properly. This would rule out a spark issue that is possibly one cylinder only. Maybe a wire didn't get crimped right or the cap is deformed.

cpandrewschmidt

Thanks guys, I'll try both tonight and report back. I'm 99% sure that timing is right. I did the timing belt in December and drove it back and forth from rimrock road to verona a couple times without issue before performing the plug and were changed. I did those in February.

cpandrewschmidt

Did the plug check over lunch. That checked out fine. Unpluged each one, the engine would change sound a bit, then as I got the wire close to the plug you could hear each one spark. After connecting the engine sounded normal. So, I don't think there's a misfire issue.

When I do the smoke test tonight I think this is the correct brake booster line to disconnect? There are two in this area, one right on top of the other.

B C

Pick a different line , you will have a tough time removing that one. What are you using for the smoke test?

jc43089

Maybe it would be easier to unhook the ICV and use that connection.

Obviously getting a Sam's Club pack of Swisher Sweets and hyperventilating into the intake?

cpandrewschmidt

I could use the ICV but then won't I be missing if there's a leak from that a point forward through the airbox? Is there a better part in the system to blow into to capture everything? At the fuel pressure regulator hose? If so, should I blow from point 1 or 2 attached? Thanks, never done this before, should be fun.

Yeah, just using some old cigars. Gonna have to be sure not to inhale too much or I'll get a mad buzz. Wait, or maybe I should?

Andrew

WIBIMMERS

1991 325i m20 help, madison