bogging bad under acceleration

fastazzcar7877 · Post by **fastazzcar7877** » Sun Aug 31, 2014 8:48 am

I have a 1980 528i and i have no idea why but when the car warms up it bogs really really bad under acceleration .. like right around 2k rpms. It almost shuts down it bogs so bad. I was thinking it could be something to do with the afm but im not sure. The previous owner hard wired the in tank pump to be the primary and i thought that it had something to do with it so i replaced the in line fuel pump and rewired it the way it was supposed to be.. and still its missing like that . The thing that made me think it was the fuel pump is when it gets warmed up after a while the fuel pump starts getting louder . Any help will work . Ive got the afm off now and was about to start trying to take it apart and clean the contacts and adjust the air fuel ratio in that but i dont want to get into something that i really have no idea how it works. Im just kinda lost on this one and cant figure it out ..

fastazzcar7877 · Post by **fastazzcar7877** » Mon Sep 01, 2014 1:03 pm

does anyone know if any other maf wil work with my car? like a m30b35 out of an e28? or a 635?

fastazzcar7877 · Post by **fastazzcar7877** » Mon Sep 01, 2014 4:30 pm

Ok. So I took my afm apart and cleaned all the contacts. It seems as though it's a fuel loss problem. I bypassed the fuel filter thinking it could be clogged up. It ran a little better. Pulled a lot harder in higher rpm but still would hit a brick wall from a dead stop at almost exactly 2000 rpm. Still can't figure it out. Also. Should the in tank pump even be running while the car is running?

fastazzcar7877 · Post by **fastazzcar7877** » Mon Sep 01, 2014 4:57 pm

Does anyone know the stock fuel pressure for my car? How many psi?

Mike W. · Post by **Mike W.** » Tue Sep 02, 2014 8:59 pm

fastazzcar7877 wrote:Does anyone know the stock fuel pressure for my car? How many psi?

IIRC it's 32PSI at idle. It will increase with load or if the vacuum hose is disconnected.

Lenny D. · Post by **Lenny D.** » Wed Sep 03, 2014 2:19 am

Make sure your main pump is correctly wired. The in tank will not produce enough pressure to run the system.

High RPM bogging can be attributed to component breakdown inside the ICU (ignition control unit - on the right side fender in the engine bay).

fastazzcar7877 · Post by **fastazzcar7877** » Wed Sep 10, 2014 12:48 pm

is there a way to test the icu?

Lenny D. · Post by **Lenny D.** » Thu Sep 11, 2014 12:37 am

Swap with a known functioning one.

Start simple first - Clean the ICU connector; inspect/change HT wires, especially the center one to the coil . . .

fastazzcar7877 · Post by **fastazzcar7877** » Thu Sep 11, 2014 7:46 pm

ok so. i just checked the fuel pressure before the regulator and either im tripping or something is seriously wrong. It was 4psi. right before the regulator on the feed line from the pump.

fastazzcar7877 · Post by **fastazzcar7877** » Thu Sep 11, 2014 7:47 pm

ok so. i just checked the fuel pressure before the regulator and either im tripping or something is seriously wrong. It was 4psi. right before the regulator on the feed line from the pump.

fastazzcar7877 · Post by **fastazzcar7877** » Thu Sep 11, 2014 8:15 pm

nevrmind. im retarded and checked the return to the tank. lol ... no wonder it wasnt what it was suppose to be. ill check this weekend and see whats going on.

fastazzcar7877 · Post by **fastazzcar7877** » Mon Sep 15, 2014 3:41 am

So I fixed it. Apparently the previous owner installed a fuel pump in the tank and had no idea what they were doing. The small hose that connects the fuel pump to the unit itself had no clamps on it whatsoever. Which means when it was trying to pump gas to the main pump it was like trying to drink through a straw with a hole in it. It had no suction at all. Also the wires were just twisted together in the tank. Lol. Real smart. So I wired it right and fixed the hose. Put a new strainer on and BAM. Lol. So thanks everybody for the advice and info. The beast is back.

Lenny D. · Post by **Lenny D.** » Mon Sep 15, 2014 11:57 am

Congrats. You get a gold star on you forehead for the day!

See my post on the 'fuel scavaging' thread . . .