Same problem: car dies/bogs down at ~3000rpm under load (updated)

[Andy348]

Car: 1986 325 w/1987.5 325is swap
I had this problem about a month ago, tested the fuel pressure and realized the in tank fuel pump was dead. I replaced that this weekend, and tested the fuel pressure. Everything seems okay, but you tell me:

http://www.youtube.com/watch?v=Y98Mj34C1TE

So I take the car around the block, and it seems okay in first gear, but it hesitates quite a bit. About a minute in, once you go past 3500rpm or so in 2nd gear, it starts bogging down hard and stumbling. It seems like if I would clutch in and rev it would keep help a little. Heres the video (skip to around 1:50 unless you want to get really dizzy):

http://www.youtube.com/watch?v=5EfS7Lyz7kY

Now I doubt its a fuel problem, because if I undo the battery for 5 mins then drive around I manage to get it past 3500rpm (with a little bucking every once and awhile). I figure its a sensor that's gone haywire.

I'm going to test the TPS, CPS and see if I can test the AFM. I'm wondering though if it could be caused by anything in the glovebox, as there are some things disconnected (hence the tachometer not registering the idling revs).

If anyones got any suggestions I'd be thankful. I haven't been able to drive the car for about 4 months and I'm getting very pissed off.

Andy

[jlevie]

When you are driving the car and it bogs, what is the rail fuel pressure?

[dannyyisntt]

Sounds similar to what my buddy's car is doing. I'd also like to know what causes this.

[Andy348]

When you are driving the car and it bogs, what is the rail fuel pressure?

I'll check that tonight.

[Kommando]

Have you ever adjusted the valve lash?

Mine didn't start doing that until I adjusted my valves, got distracted by someone talking to me and, I missed one and was not the right spacing and that is what happened afterwards.

[Andy348]

Nope, I haven't adjusted the valves but the previous owner of the engine might have.

[Kommando]

It could be unrelated, but that's when I noticed the issue with mine.

[Andy348]

Just checked the fuel pressure when it bogs down. It drops down to roughly 10 and it won't' let me accelerate.

I've already got a new in tank pump, fuel pump and fuel filter. What the hell can it be?

[jlevie]

A bad FPR, rust in the tank, a bad soft fuel line, a probem with power/ground to the pump, or even a bad pump are possibilities.

[Andy348]

Got in a new (used) fpr, made it a lot smoother but still got the same problem. That gas has been in there for awhile, so I might try and drain that and replace it. I don't know how to check bad grounds/power if the problem only happens when driving at 3500rpm, any suggestions? edit: any chance it could be from a fuel line thats a little small? The one I've got from the filter to the rail doesn't seem to fit over the rail very well and I figure it might be too small. It will still go on and stay on, albeit with force.

[Andy348]

Anyone?

[ak-]

Same symptoms as me a while back.
Turned out to be the cap/rotor.

http://www.r3vlimited.com/board/showthread.php?t=195935

When I mention somewhere in the details that it "won't go", it was hitting a wall around 3k RPM just like you.

I went through a new CPS, TPS, and o2 sensor and we finally took of the cap to see that the 6 metal points inside of it were very worn. We hit it the metal points with some sand paper to clean it and it ran much better. So after purchasing a new one, problems went away!

Goodluck

[Andy348]

Thanks for the input. I'll try and sand it down and see if it does anything.

How would that cause my pressure to drop though?

[dannyyisntt]

Just resolved a similar issue yesterday by cleaning/sanding the cap and rotor (new ones are on their way), replacing the plug wires (were siliconed together by the po) and replacing the plugs and afm.

Basically a light tune up. Still get a slight and hardly noticeable hesitation when you first start the car and go over three grand, but after it does it once and the cars still running, it won't do it again. I believe the new cap and rotor will completely eliminate the issue with my vehicle.

[Andy348]

Just removed the cap and rotor and they looked practically brand new. One problem though, once I reinstalled it and started the car up, its shaking terribly and nearly dying constantly. I haven't done anything else since the last start up (which didn't have these problems) so I figure that the cap/rotor has gotta be bad. I'll try and swap one out soon.