Low RPMs bucking

[MuRCieLaGo]

Originally Posted by LGAFF

one under the ecm

Oh! Yes it's plugged in!

[WVZR-1]

You've much to consider and it's been since "day one" so ... a pair of pumps, then there's that what's thought to be repaired ECM pin. What terminal on which connector did that turn out to be? I believe there were three possibilities.

[MuRCieLaGo]

Originally Posted by WVZR-1

You've much to consider and it's been since "day one" so ... a pair of pumps, then there's that what's thought to be repaired ECM pin. What terminal on which connector did that turn out to be? I believe there were three possibilities.

-Repaired ECM pin: can't tell you which terminal. When it was unpinned, the car ran like total crap. It was a ground. But like I said, the shop who repaired it is serious and they have a strong reputation, including from myself in the past.

-Pair of pumps: how do you test the pressure?

-Spark plugs: ordered some new plugs, will be receiving them shortly.

-o2 sensor: I'd like to find a way to test them without having to remove them.

-Coil pack/spark plug wires: not sure how to do this, but there must be a way to test them.



Worst than ever today.

Just before it gets fully warmed up, the car pulled OK. Then, it ran like crap again.

I joined a video, in which we don't really see the misfires, but we can feel the sudden power loss.

https://www.youtube.com/watch?v=cQb882XCwK8

For what it's worth, I'm changing the fuel filter tomorrow.

Should I ask a local tuning shop to run the car on a dyno to help me with the problem?

[A26B]

Just before it gets fully warmed up, the car pulled OK. Then, it ran like crap again.

Before it warms up, it's running in open loop. Switches to closed loop after warmed up.

In open loop;
(1) both primary & secondary fuel pumps are operating,
(2) O2 sensor input is not used.

Obviously NOT fuel filter, coils, plugs or plug wires if it runs fine in open loop.

May be primary fuel pump or O2 sensor.

You do not need to dyno, only data log & look at O2 counts. You should also do a static fuel pressure test & isolated each pump to verify pressure output & leakdown.

[MuRCieLaGo]

Originally Posted by A26B

Before it warms up, it's running in open loop. Switches to closed loop after warmed up.

In open loop;
(1) both primary & secondary fuel pumps are operating,
(2) O2 sensor input is not used.

Obviously NOT fuel filter, coils, plugs or plug wires if it runs fine in open loop.

May be primary fuel pump or O2 sensor.

You do not need to dyno, only data log & look at O2 counts. You should also do a static fuel pressure test & isolated each pump to verify pressure output & leakdown.

Last fall, I had similar bucking problems, only when the Valet key was turned off.

I got no idea how to data log this... And I'd love to know how to run a fuel pressure test!

But if it runs fine in open loop as you suggest, can't we eliminate the primary fuel pump theory? I'll let the car cool down again and I'll go for a ride tonight, to confirm it runs fine in open loop.

Thanks a lot for your help!

[A26B]

You cannot eliminate the primary fuel pump in open loop operation. Both the Primary & Secondary fuel pumps will run in open loop, masking a problem with one fuel pump. In open loop, the Secondary fuel pump may be the only pump operating to spec. Accordingly, when the engine warms to operating temp & goes into closed loop, the Secondary is on standby & not running. Only the Primary fuel pump runs in closed loop, which is when your problem occurs, hence the need to isolate & check each fuel pump, particularly the Primary.

The procedure for performing a static fuel pump test has been discussed many times & should be easily found searching the archives. I'll wager Dynomite has is tagged in Solutions

[MuRCieLaGo]

Originally Posted by A26B

You cannot eliminate the primary fuel pump in open loop operation. Both the Primary & Secondary fuel pumps will run in open loop, masking a problem with one fuel pump. In open loop, the Secondary fuel pump may be the only pump operating to spec. Accordingly, when the engine warms to operating temp & goes into closed loop, the Secondary is on standby & not running. Only the Primary fuel pump runs in closed loop, which is when your problem occurs, hence the need to isolate & check each fuel pump, particularly the Primary.

The procedure for performing a static fuel pump test has been discussed many times & should be easily found searching the archives. I'll wager Dynomite has is tagged in Solutions

Thanks a lot for your explanations! I'll concentrate my efforts in testing the fuel pumps now. Performing a fuel pump test seems to be quite easy, except that I'm not sure where to plug the "T"!

I just took the car for a ride (wasn't fully cooled down) and it's running way better, without any reason. I had it reach operating temperature and it's still running strong.

I just don't get it.

https://www.youtube.com/watch?v=dMGc9vCqdoM

[A26B]

Here's an old post for pump testing.

There are 2 fuel pumps, FP1 is the primary and FP2 is the secondary pump. For a cold start, both FP1 & FP2 will run until the engine reaches appx 176F, then FP2 will shut off. For a hot start, above 176F, both FP1 & FP2 will run, but after 2 sec, FP2 will shut off.

To determine the functionality of the pumps, they must be tested separately. There are 2 fuses. FP1 fuse is on the pass side of the dash in the fuse panel. The fuse is labeled FP1. FP2 fuse is under the passenger side dash kick panel. Remove the panel. The fuse is labeled FP2.

The procedure to check fuel pumps is as follows;

Cold Engine
Key off, Engine off
Attach Fuel pressure gauge line to fuel rail. Bleed down any pressure in the rail.

Testing FP1 (Primary Fuel Pump)

1. Remove FP2 fuse.

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

Testing FP2 (Secondary Fuel Pump)

1. Replace FP2 fuse and remove FP1 fuse

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

6. Replace FP1 fuse.

[MuRCieLaGo]

Originally Posted by A26B

Here's an old post for pump testing.

There are 2 fuel pumps, FP1 is the primary and FP2 is the secondary pump. For a cold start, both FP1 & FP2 will run until the engine reaches appx 176F, then FP2 will shut off. For a hot start, above 176F, both FP1 & FP2 will run, but after 2 sec, FP2 will shut off.

To determine the functionality of the pumps, they must be tested separately. There are 2 fuses. FP1 fuse is on the pass side of the dash in the fuse panel. The fuse is labeled FP1. FP2 fuse is under the passenger side dash kick panel. Remove the panel. The fuse is labeled FP2.

The procedure to check fuel pumps is as follows;

Cold Engine
Key off, Engine off
Attach Fuel pressure gauge line to fuel rail. Bleed down any pressure in the rail.

Testing FP1 (Primary Fuel Pump)

1. Remove FP2 fuse.

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

Testing FP2 (Secondary Fuel Pump)

1. Replace FP2 fuse and remove FP1 fuse

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

6. Replace FP1 fuse.

Seems to be quite easy, except for that "Attach Fuel pressure gauge line to fuel rail." part. Pretty sure I'll have to remove the plenum, isn't there a way to attach it in the tank?

Thank you very much Jerry, I really appreciate that!

[secondchance]

Originally Posted by MuRCieLaGo

Seems to be quite easy, except for that "Attach Fuel pressure gauge line to fuel rail." part. Pretty sure I'll have to remove the plenum, isn't there a way to attach it in the tank?

Thank you very much Jerry, I really appreciate that!

You do not have to remove plenum to attach fuel pressure gauge. Front of fuel rail on the passenger side has a Schrader valve readily accessible. There is an aluminum cap similar to tire valve stem cap.