M20 Power Loss, Check My Diag.

[David325e]

Hey guys, I've been loving driving the E30 for the past few months. 87 325is budget car. Lately (within two months of beginning to drive it regularly) I'm having acceleration issues. I've replaced the intake boot, cleaned ICV, Maf, replaced visibly cracked vacuum hoses, checked with tbc for vac leaks at the gaskets. Head of this car was off ~2k miles ago, gasket etc all replaced. Exhaust is tight, cap/rotor and plug wires were replaced with head work.
The car drives well overall, has plenty of issues but nothing major. Unless I'm leaving a dead stop. If I put the throttle 1/3-1/2 way down the car accelerates fine. If I mash the pedal the car bogs down, stays at idle speed and on one occasion stalled. When it bogs down I have to coast until the car reaches about 1200rpm then I can accelerate. When hitting the kickdown switch at any speed above 0mph the car reacts as normal.
I pulled the plugs this afternoon and all were normal wear, no deposits or discoloration.
I know the oxy sensor needs to go (no idea on age and car runs rich) but I've driven M20s with bad 02s before and not had this symptom. My best guess is bad fuel filter. No idea on the age of it. This sound correct? And I have an unused filter made to fit an M60 car (94 540), could I put that in the place of the stock one long enough to run the car, or will I cause more damage.
Lastly, what are common symptoms of having a clogged/bad cat on the E30? If its not a fuel filter my only other guess is back pressure from a plugged cat.

Cliffs: car with man tune-up parts replaced bogs at full throttle from a stop. Clogged fuel filter?

[jlevie]

It could be a fuel delivery problem or a bad spot in the resistance trace in the AFM. Change the fuel filter and then run the suite of fuel system tests in the Bentley manual. They will reveal whether there are any fuel delivery issues. The easiest way to diagnose the AFM is to swap in a known good unit.

You could also have a bad WOT switch in the TPS, or the throttle and TPS could be misadjusted.

[David325e]

It could be a fuel delivery problem or a bad spot in the resistance trace in the AFM. Change the fuel filter and then run the suite of fuel system tests in the Bentley manual. They will reveal whether there are any fuel delivery issues. The easiest way to diagnose the AFM is to swap in a known good unit.

You could also have a bad WOT switch in the TPS, or the throttle and TPS could be misadjusted.

Thanks Jim. Wouldn't a bad WOT show up with WOT at any speed? I'll check the TPS, no idea on it's condition. Any thoughts on running an incorrect fuel filter temporarily?

[SpecM]

the fuel filter should work fine, as long as it fits demontionally

is your e30 and automatic? Mine is slow as hell off the line but that's because of the tranny. It sucks.

[David325e]

Yes auto. The unit behaves fine elsewhere. I've driven a dying 422 for about 20k miles and its nothing like that. This is most certainly the engine loosing almost all power when accelerating from a stop, not just a slushbox slow.

[SpecM]

oh

whats a 422? is it like an Olds 442?

[David325e]

4 HP 22, the auto in e30s, some e28s and e34s.

[SpecM]

oh OK. I know what a 4hp22 is, I've never heard it called a "422" before

[David325e]

Haha sorry, my laziness. For the most part I'm on bf/c E34 section and the 20-30 of us regular guys all use the same shorthand.

Sidenote, living in a house with no garage is killing me. Been with the E30 all day and want to go back to it. Nothing like a new project.

[jlevie]

Thanks Jim. Wouldn't a bad WOT show up with WOT at any speed? I'll check the TPS, no idea on it's condition. Any thoughts on running an incorrect fuel filter temporarily?

Yes, a bad WOT switch should cause problems at any speed. As should a fuel delivery problem. But when the engine is trying to go from idle to higher rpm with a wide open or nearly wide open throttle it is more sensitive to anything that upsets the A/F ratio.

On further thought, I'd want to see a smoke test not find any leaks before I'd seriously consider other possibilities.

[David325e]

Fair enough. The rear valve cover stud closest to the fender is broken. Carb spray didn't reveal any change in idle and theres no oil leaking from the area. Still a possibility of that causing a vac leak, and recommended fixes?

[jlevie]

I doubt that would result in enough of an intake leak to matter, but given the location hitting it with carb cleaner proves nothing. Carb cleaner only works on leaks very close to the intake valves. Only a smoke test will reveal all intake leaks.

The fix for the broken stud depends on whether the stud is broken off flush with the head. If there's enough sticking up to grab with vice grips, removal and replacement is easy. Otherwise careful drilling and use of an easy out is indicated.

[David325e]

For those that come across this in search, jlevie is right as usual haha.

The studs for the valve cover are M6 x 35mm studs threaded into the head with threadlock on them. Methods for getting one with any length on it out are: vise grips, weld on a bolt and turn it out, stud extractor.

[David325e]

Weather and interviews have kept me from looking at the car. But I did notice today that the car only does this in gear. In neutral it will rev from an idle with no problem. I didn't think to try going from brake to pedal in neutral, but I'm beginning to suspect among other things a vacuum leak at the booster.