eta Won't Run Smoothly Above Idle

[davintosh]

I'm finally getting around to doing some troubleshooting on my eta. It had been running like a champ, then started acting up all of a sudden a few weeks back. I drove the thing to a wedding about a half hour away and it was running great (some back country roads with some twisties, so I had a little fun!) but a couple hours later on the way to the reception it started bucking a bit at speed; when we got to the reception, it wouldn't run smoothly at all above idle. Since then, most of the time it will start with no problem, but once it's running, give it any throttle at all it misfires and bucks. Bump the throttle up a bit & try to keep it above idle it'll sputter and die. If you start it & leave it at idle, it'll run all day, rock solid at about 700 rpm, but touch the throttle and she's totally undrivable. But then again it's undrivable at idle too.

I did some searching & found a few posts that were somewhat similar to my situation; so far I've replaced the fuel filter, verified the TPS is adjusted & working properly, replaced the coolant temp sensor, replaced the main & fuel pump relays, checked & cleaned all the fuses, checked & cleaned the battery cables & the main ground from the battery. No change in behavior. Following Andy's advice I cobbled together a makeshift fuel pressure gauge using an old water pump gauge that I had on-hand with a hose barb; it read about 22 lbs. According to the Bentley, it should be around 36 lbs, correct? Would low fuel pressure lead to symptoms like I have? And would the fuel pump suddenly flake out halfway & make a car that was running great one minute run like crap the next, but still idle ok?

Any other ideas of what the problem might be? Ignition? ECU?

[demetk]

I'd put another pressure gauge on there to verify. 22psi is very low and the FPR should be regulating fuel pressure.Try this first, clamp the return fuel hose and see whether the pressure spikes. If it does, first replace the FPR with known good. If it doesn't replace the pump.

[Son of a]

Check the ecu. If you're lucky its that simple and the fuel pressure gauge is wrong. If you throw in another ecu, and it still runs like crap, pull the RR wheel and measure the pressure straight out of the pump. Without the FPR in the way, a good fuel pump should put out a shocking amount of pressure (100 PSI+, enough to blow the hose clamps (AMHIK)).

Also, my M30 once exhibited the same problems when a slight molding void in the distributor caused arcing on the cylinder #3 plug wire. Car ran just fine up until 4k, and slowly that number came down more and more until the problem occurred everywhere above idle. Could be on the electronic side of the ignition, if its not something big like the ecu.

I would pull the plugs, continuity test the wires, test the coil, look at the distributor, look at the rotor, re-test the CTS and the TPS. If all of that comes back in spec., open the AFM. If I had to guess, its either a really weak fuel pump (though I kinda doubt that) or more likely, something causing a weak spark. But who knows.

[davintosh]

Check the ecu. If you're lucky its that simple and the fuel pressure gauge is wrong. If you throw in another ecu, and it still runs like crap, pull the RR wheel and measure the pressure straight out of the pump. Without the FPR in the way, a good fuel pump should put out a shocking amount of pressure (100 PSI+, enough to blow the hose clamps (AMHIK)).

Also, my M30 once exhibited the same problems when a slight molding void in the distributor caused arcing on the cylinder #3 plug wire. Car ran just fine up until 4k, and slowly that number came down more and more until the problem occurred everywhere above idle. Could be on the electronic side of the ignition, if its not something big like the ecu.

I would pull the plugs, continuity test the wires, test the coil, look at the distributor, look at the rotor, re-test the CTS and the TPS. If all of that comes back in spec., open the AFM. If I had to guess, its either a really weak fuel pump (though I kinda doubt that) or more likely, something causing a weak spark. But who knows.

You get the prize on this one; it was the rotor. Of course I had to muck with a bunch of other stuff yesterday and today before I got around to pulling the distributor cap off; once I did that, the problem was blindingly obvious. I ought to post a photo of the rotor; part of it was melted pretty severely and the melty parts looked like spider webs inside the dist. A few loose chunks as well. I think I'll pick up a fresh distributor cap too and a second rotor, and keep a spare set in the spare box.

Before figuring out the real problem, I swapped out the fuel pump with a known good one; same symptoms. Tested the fuel pressure at the pump, and you were right; pegged the gauge at over 100 psi! I also swapped in a slightly flaky ECU (no improvement) and located someone in the FS section that had an ECU for sale and bought it. I figure none of this was for naught though; I'll just add a few things to my box of spares.

Thanks for your help!

[rodpaine]

I ought to post a photo of the rotor; part of it was melted pretty severely and the melty parts looked like spider webs inside the dist. A few loose chunks as well. I think I'll pick up a fresh distributor cap too and a second rotor, and keep a spare set in the spare box.

No question about your rotor condition! The rotor can cause some performance issues and still look reasonable to many who have checked it. Here is one from 'waynet' that he sent for me to post on my web site, so that others could see what a known trouble maker actually looks like. The contacts in the cap looked the same. Not bad enough to be a problem in some folks opinion, but this amount of wear is the problem in many 528e M20 ignition systems. Believe me.
FWIW,
-Rod

[davintosh]

Bosch is appears to be the OEM brand for dist caps/rotors, but mine was not Bosch; do other brands tend to be problematic, or do people have decent luck with them?

[Son of a]

Bosch is appears to be the OEM brand for dist caps/rotors, but mine was not Bosch; do other brands tend to be problematic, or do people have decent luck with them?

The recent replacement distributor on my 533i was a Bremi. To be honest, I try to avoid Bosch replacement parts when possible. Too many horror stories (firsthand, secondhand, and otherwise anecdotal) about NiB failures.

Glad it turned out to be something simple in the end.

[davintosh]

Your example looks to be in a tad bit better shape than mine; if that one was causing issues, it's a wonder my car would even run at all.

[rodpaine]

I've seen some really bad condition ignition parts on a lot of 528e engines in my time, but yours is certainly the worst I've ever seen! You're sure it was actually running?
-Rod

[davintosh]

I've seen some really bad condition ignition parts on a lot of 528e engines in my time, but yours is certainly the worst I've ever seen! You're sure it was actually running?
-Rod

Well, yes, if idling counts.

What brand ignition components do you use, Rod?

[TSMacNeil]

Holy crap, Dave...
That eta still started and idled?
What amazing machines....

[Rich Euro M5]

Your example looks to be in a tad bit better shape than mine; if that one was causing issues, it's a wonder my car would even run at all.

By any chance does your eta have aftermarket spark plug wires?

Rich

[davintosh]

By any chance does your eta have aftermarket spark plug wires?

Rich

Why yes, it does. The rotor was a cheapo plastic aftermarket unit, and the cap looks to be an aftermarket item as well. I was wondering whether I should replace that; prolly the wires too, and the plugs whilst I'm at it. I remember the PO telling me that he had spent a bunch of money on a tune-up the summer before I bought it; I think he got taken for a ride.

I had to stop at several local parts stores today before finding one that had a rotor in stock. It was a Bosch, and the difference between the two rotors was pretty remarkable; the old was plastic and felt flimsy, but the Bosch felt more like ceramic. Got the new unit installed a little while ago and it runs like it's supposed to. I'm going to order a new cap, wires & plugs, then tuck the current set into my spares box (maybe someday mine will be as well-equipped as Matt's )

[turbodan]

F&#k!

I wonder if the aftermarket wires had enough resistance. Stock wires have several thousand ohms IIRC.

[thrty8street]

glad you fixed it

[Alfonso Bedoya]

You're best bet is match up Bosch cap and rotor if you can, Beru makes pretty good caps and wires. From what I've read the different companies out there use different materials.

Not good to mix and match when it comes to cap and rotor, jus sayin. That rotor looks like it's been through WW3! That is up there with turbo dan's exploded vavles!!!