'84 eta surging

[Varinn]

Hey, I've been having a strange problem with my car since I bought it a month or two ago and it's time for me to start digging into it.

It's a 1984 eta, 5-speed. The car has a rebuilt head, new timing belt, water pump, clutch etc. Too much to list, all work performed within the last year by a very reputable BMW shop in the area.

Under heavy load and especially in the lower 3 gears the car has a tendency to surge power on and off. It's hard to explain, and almost impossible to capture on video. It's as if the car is cycling between full throttle and half throttle every half second or so. I've checked the basics, spark plugs, air filter, AFM (clean), no noticeable vacuum leaks that I can find.

I'll hopefully be installing a MarkD chip in the next couple days which should rule out and possible tuning issues (as I have heard this is relatively common with ETA's)

Any other suggestions on where I can look?

[davem]

Hey man from what I've read on here sounds like it might be a fuel issue?

[MR 325]

I thought all Etas did this, lol. "shrugs"

[Boostesi]

hunting the same exact problem, found a few vac leakes and fixed them, didnt help much. i checked fuel pressure, 20 psi low, changed the inline fuel pump with a tre pump, and it has cleared up alot, although i think the coolant temp sensor might be bad, because sometimes when i start the car it is extremely rich for the first minute or two... but since the fuel pump it has got better, let me know what you figure out, good luck! lol

[Varinn]

I installed the MarkD chip and converted from an 021 to an 027 DME today and the problem has completely dissappeared. I was hoping for some improvement, but it solved it entirely! A highly recommended upgrade, the car feels completely different. The extra grunt has totally smoothed out engine operation. Shifts are smoother, less jerky on and off the throttle, smoother acceleration up hills and from starts. Well worth the money

[matt0300]

Wot trigger bad? What's ur fuel pressure at?

[Kershaw]

o2 sensor?

use a 1990 mustang 5.0 o2 sensor. for $40 you might as well do it anyway. just splice the wires.

[matt0300]

Wow I'm surprised no one said o2 sensor. It does sound like its getting bad a/f mixture so afm or o2 would be the first places to look.

[MR 325]

Did you guys even read his reply to the thread?

[Varinn]

I installed the MarkD chip and converted from an 021 to an 027 DME today and the problem has completely dissappeared. I was hoping for some improvement, but it solved it entirely! A highly recommended upgrade, the car feels completely different. The extra grunt has totally smoothed out engine operation. Shifts are smoother, less jerky on and off the throttle, smoother acceleration up hills and from starts. Well worth the money

;)