Intermittent bucking problem

[slo325i]

Hey guys,

After searching for hours and hours... i've yet to find out the problem.
Now, let's figure out a diagnosis:

Patient info
1987 325 with m20b27 eta motor

Sign and symptoms:
1. Intermittent bucking/jerking when I take off normally from a light
2. Intermittent bucking/jerking while cruising on hwy in 5th gear
3. Fuel economy/econometer gauge jumps left and right as the motor "pauses" which I think is causing the bucking/jerking.
4. No CEL light.

Interventions done:
1. Distributor cap
2. Rotor
3. coil
4. spark plugs/wires
5. crank position sensor
6. fresh oil
7. new battery with new ground cable
8. fuel pump relay
9. fuel pump (under the back seat)
10. alternator
11. Sprayed/brushed/lubed all connections
(coolant sensors, CPS, injectors, TPS, relays)
12. FPR (brand new)

Interventions not done yet:
1. Fuel pump under the driver seat
2. O2 sensor
3.
4.

I'm really lost as to why my car's having these intermittent issues. And when I say intermittent, it really is... only happens 4~5% of the time while driving. It's not on constantly at all. I just got back from 5 hour drive with this car and it was a fantastic ride, smooth and everything... It's just when i take off from 1st gear, it bucks/jerks/pauses around 2000rpms. After that it's smooth sailing...

Please help.... Running out of ideas :neutral::neutral::neutral:

Justin

[vr2jetta]

Ahhhh, the infamous 2k bucking problem. I have been having issues with mine too. I have noticed on mine it only does it when I fill the tank. After it gets past 3/4 it drives fine. My fuel pump has started whining louder lately so I am guessing that is going to be the culprit. For good measure I also ordered a new DME relay and fuel pump relay. Good luck with that.

[slo325i]

anyone else??

I've also replaced the main relay. My fuel pumps don't whine at all , that's why i haven't felt the need to replace the pump under the driver's seat. I'll try to get a gauge to see what fuel pressure's like though...

Please help...

Justin

[che13]

MAF - could be the culprit

[slo325i]

Oh yea... replaced that too... as well as the throttle body and TPS

[slo325i]

Could it be related somehow with my fuel/econo gauge??

Because when the car jerks, so does the econo gauge.

Anyone??

[yert315]

Have you tried swapping in another ecu or checked your coolant temp sensor?

[slo325i]

About the coolant temp sensor, exactly which one is it? Is it the brown one with a single wire or the blue one with two wires attached? I've cleaned, and lubed connections there as well. I do have bunch of spare sensors though.

Also, currently, i'm running a 153 ecu. I have a spare 173. Should I try swapping it or not? i dont' want to cause any damages though. I hear it's actually a direct bolt-on upgrade. but i'm not too sure...

[vr2jetta]

Coolant temp sensor is the blue one, the brown one goes to the gauge.

[yert315]

About the coolant temp sensor, exactly which one is it? Is it the brown one with a single wire or the blue one with two wires attached? I've cleaned, and lubed connections there as well. I do have bunch of spare sensors though.

Also, currently, i'm running a 153 ecu. I have a spare 173. Should I try swapping it or not? i dont' want to cause any damages though. I hear it's actually a direct bolt-on upgrade. but i'm not too sure...

it's the two wire one, like vr2jetta said. give it a shot if you have an extra.

also, I'm not that familiar with the eta motors, but I do not think the "i" ecu will work with them. If you can source out another eta ecu, that would be your best bet.

[slo325i]

the 153 ecu's a 87 325i ecu. Which rev'ed a little lower than the 173 ecu's which came out on later 89 325i.

[slo325i]

To make the long story short, the PO installed an eta motor in the 325i motronic 1.3 harness with the 153 ecu. I dunno how he ghetto fabbed it together but it runs really well other than the bucking symptom at hand. I mean, i heard that the eta injectors were high impedance whereas the i injectors were low impedance. I guess he swapped out the injectors too because like i said, the car runs really well.