Stumped with performance problem

[mrgraphics]

I bought a 1986 325es autotragic, and I'm having a performance problem. Driving around normally up to 2K rpm, the car behaves fine. But if I press on the gas hard, it just doesn't go. One night when nobody was on the streets I really tried laying into it. It rev'ed to 2300 RPM, started bucking hard, and then suddenly shot up to 4500 rpm. When entering the highway it seems like it doesn't matter how much gas I give it - it just doesn't rev above 2K.

The other thing it does: It starts up great cold, but when warm I sometimes need to crank it ALOT. Also when starting cold, the first time I try to give it gas it stutters a bit, and then picks up. Once warm it runs fine up to 2k.

What I've done:
Checked for vacuum leaks
Replaced fuel pressure regulator
Replaced CPS and speed sensor
New Plugs (copper)
New cap and rotor
Removed both fuel pumps, replaced with in tank Tre Performance
Installed one way fuel valve at the pump
Valve job
New O2 sensor
ECU swap - chipped (non-ebay, real)
New Fuel Filter

I also think I'm getting pretty poor gas mileage. Hard to tell because I've been laying into it trying to figure out what's going on.

Any ideas on where to go from here? All I can think of is leaking / clogged injectors.

[AndrewBird]

Does it only do it when at full throttle, or at any throttle position? Mean, can you rev above 2k if you accelerate slowly?

[Earendil]

Could be a clogged cat. I had a similar list of known good parts, and checked everything but the 3 year old cat. Finally checked it by pulling the O2 sensor out, and finding that it ran much better. Entire saga for reading is here, but I'll just link to the conclusion

http://www.r3vlimited.com/board/showthread.php?p=2914170#post2914170

[mrgraphics]

Nitro: Sometimes it'll accelerate, but it seems like it shifts at 2K, so it never really has the chance to go that high. If I can get it into passing gear, sometimes it'll accelerate, other times it'll just sit at the same RPM and do nothing. It won't accelerate up a hill, but down I can get it to rev higher.

Earendil: I thought about that too, but didn't want to face that music. I was told to hit it with a rubber mallet and listen for chucks rattling around. Undoing the O2 sensor seems simpler. Before I recently replaced the O2 sensor, it would accelerate above 2K, but in surges: 2k, 2.2k, 2.5k, etc. in 1 second increments. I thought the O2 sensor was switching slowly causing a rich / lean seesaw effect . . . and thus I installed a new one. But perhaps since it was so old and barely working, it was half disabled (if that makes sense?)

But what would cause the hard hot start issue?

[Earendil]

Nitro: Sometimes it'll accelerate, but it seems like it shifts at 2K, so it never really has the chance to go that high. If I can get it into passing gear, sometimes it'll accelerate, other times it'll just sit at the same RPM and do nothing. It won't accelerate up a hill, but down I can get it to rev higher.

Earendil: I thought about that too, but didn't want to face that music. I was told to hit it with a rubber mallet and listen for chucks rattling around. Undoing the O2 sensor seems simpler. Before I recently replaced the O2 sensor, it would accelerate above 2K, but in surges: 2k, 2.2k, 2.5k, etc. in 1 second increments. I thought the O2 sensor was switching slowly causing a rich / lean seesaw effect . . . and thus I installed a new one. But perhaps since it was so old and barely working, it was half disabled (if that makes sense?)

But what would cause the hard hot start issue?

If it stumbles around, it may not be the CAT. When I experienced a clogged cat, it idles more or less okay (until it got really bad), and it sounded smooth at all times. But it was like with ever 50rpm the HP was cut in half, so that by the time the car reached 2000rpm it just had nothing left to give. Like, absolutely nothing.

If it surges or hesitates and sometimes climbs and other times doesn't, or it has dead or erratic spots in the RPM range, I'd say it's the Air Flow Meter (AFM). To diagnose my own AFM for a slight loss of power at high RPM, I once tossed a different one in there that was terrible broken and I got all kinds of erratic hesitation at 1500-2500 RPMs that was so bad the car really couldn't produce enough consistent power to get the engine up to any speed. This is caused by dead spots in the sensor track, and can't easily be diagnosed. If you can get your hands on a friends AFM, it's a 5 minute job to swap the airbox+AFM and try it out. If your problem is gone, and your friends has issues, that'll answer that problem :)

FYI: When I say remove the O2 sensor, I mean physically unscrew it from the down pipe so that the engine has a place to breath. It'll be loud, so do it someplace where the cops won't immediately start questioning you :)

[ryans09sstc]

First off, I would install a fuel pressure gauge and make sure your getting the correct pressure at the rail. It should be around 43 psi I believe. It could be leaky injectors causing the hard warm start or many other things. I would also test the engine coolant temperature sensor for the correct resistance as well.
It sounds like a fuel related problem so check rail pressure first.

Ryan

[ryans09sstc]

Also test the thermo-time switch next to the coolant temperature sensor. I believe on the 325e if it is faulty it will make the cold start injector spray at all times.

[mrgraphics]

I did crack the lid on the MAF. I did the slight adjustment so that the points were tracking on a clean section of the track (but was careful not to change any settings or alignments). The track was not that worn. I also cleaned it to make sure the flap travelled without issue. Of course this doesn't mean that it isn't bad.

I forgot to list that I did replace the engine temperature coolant sensor already. (I've done some much work to this thing, including belts, water pump blah blah blah. I can't remember it all).

Funny how things come to mind: When I replaced the O2 sensor, I noticed that the weld for the cat had a 1/4 inch gap / hole in it. So I used some thermal putty to seal up the weld. After that the power above 2K issue became worse (or it seemed as though it did.)

I unplugged the cold start injector as a ghetto way of testing. It still was difficult starting when hot, so I don't think that is it.

Thanks for the suggestions. All good stuff. I know my plan of action:

1) Unscrew O2 Sensor and see how it behaves
2) Check fuel pressure on rail
3) Swap out MAF

I won't be able to do it until this weekend, so I'll report back when done. But if anyone else has suggestions, please chime in.

[ryans09sstc]

Yeah check if the cat is plugged first because it could cause the problems as well. Sounds like your on to it

[mrgraphics]

Dang - just did a bunch of reading about cats. I'm in California, so I need a Carb-compliant cat, which is hundreds more. What would really happen if I put a 49 state legal cat on this thing?

[mrgraphics]

After some testing, I deduced that it was either fuel or breathing. I moved the one-way fuel valve from right at the tank to where the old (now gone) exterior fuel pump was. That solved the hard to start warm issue.

Then I took a mallet and started whacking on the catalytic converter. I'm not sure if I heard things rattling around or not, but now she accelerates smoothly, and I definitely noticed more power in general.

So, looks like the cat. Perhaps I broke apart the clog or dislodged it enough and the car can breathe again. Wonder if I can get away with not installing a new cat. The car doesn't smell like rotten eggs.