1989 325i - Split Second Loss Of Power When Driving

[gilber33]

Just some follow up - I replaced the TPS, but still had this intermittent hiccup. I tested the ignition coil and I guess it's supposed to read .5 ohms between the + and - terminals, mine was reading 1.2+, so I think I'll replace that. If that doesn't take care of it, that's pretty much all the spark related items.

Is it possibly the fuel pump? I don't see how if the pump cut out that the car would jolt like it does. I would assume it would keep cruising but it would run extremely lean for a second.

Again, this is not RPM dependent, it's happened while accelerating 1st gear and cruising in 5th gear at 2500 rpms.

[gilber33]

I had talked to the previous owner and he said he experienced this once in a while, too.

When I bought the car I pulled the engine, resealed it, and replaced almost everything. It has all new ignition stuff: cap, rotor, plugs, wires. Low mileage known working CPS. Coolant temp sensors. New fuel filter. The fuel pump is not new. I replaced the pan to frame ground wire.

I should clean the grounds on the fender and the passenger side.

I wish I knew if it was spark or fuel cutting out. At least that would narrow it down a bit.

[e30davie]

TPS is easy enough to test. Based on your description id almost guarantee it wont be it. Unplug it and see if it makes it better or worse.

Sounds like something fundamental like a loose wire or plug.

[gilber33]

It has happened at all rpm. While taking off at a stop light in 1st gear, cruising at 45 mph in 5th gear and anywhere in between.

I'm starting with the TPS. It appears to be original to the car.

[earthwormjim]

Now I'm not losing any electronics and the tach isn't affected. If the CPS was bad and it was cutting out, would the tach lose signal for the brief second?

Engine speed is sent to the tach by the ECU, the SI board processes it and generates the pulses to move the motor in the tach.
There is some buffering in the tach, so a brief 100 ms dip in RPM may not show up.


What RPM does this happen? Is it sub 2,000 RPM?

[gilber33]

Now I'm not losing any electronics and the tach isn't affected. If the CPS was bad and it was cutting out, would the tach lose signal for the brief second?

[earthwormjim]

There is a bus bar/connector underneath the fuse box which can come lose, C100. It is held in place by a hex socket bolt on the top of the fuse box. It's underneath the low beam and fog light relays in the fusebox.

I didn't have your issue exactly, instead things would cut out if I turned my high beams on, but I did occasionally encounter similar issues that you are having. The car would stutter, and I would lose electronics for a second or so.

[gilber33]

https://www.r3vlimited.com/board/sho...d.php?t=372569

Go through this. Good luck.

Well, that was a sad story. Basically he replaced everything possible multiple times and nothing helped. Lol

[Kershaw]

https://www.r3vlimited.com/board/showthread.php?t=372569

Go through this. Good luck.

[gilber33]

So this has happened once every several miles. I'm cruising along and all of a sudden the car jerks. When it does this the CEL flashes and more recently I noticed the Fuel Economy Gauge spikes to reading high MPGs. The tach and speedo are not affected. This all happens in less than a second, the car shudders, and it's done and the car continues on as if nothing happened.


All new ignition parts: plugs, plug wires, cap, and rotor. Low mileage, known working CPS.


Based on what I've read, I'm thinking the TPS might be bad. It's adjusted properly, but I'm thinking that the ECU is getting a faulty reading that the TPS is closed (or less than what it's actually at) and reducing the injector duty and the car is leaning out, causing the economy gauge to spike and the car to jerk.


Any other ideas or input would be appreciated.


Thanks