Jerky acceleration (did all the search)

[karol1001]

Hello. This is my first post, but I've been a reader for a while. Now I've bought my own 1gen Legacy N/A and I need your help I don't really know the category of my problem so I thought I'd put it in the Misc.

The patient: 1991 Legacy 2.0 N/A, manual
The trouble: the car doesn't accelerate smoothly. It stutters when you accelerate rapidly - especially in second and third gear. Like the fuel doesn't get in properly or something. The problem is only slight - the engine never dies and has no major issues starting (only sometimes when warm). It's just annoying because when I want to accelerate hard sometimes there is a delay in the power.

The list of things I already tacled:
1. O2 sensor
2. MAF
3. Ignition wires
4. Fuel pump
5. Knock sensor (connected or not it doesnt change anything and there is no Check Engine light)

There is some dirt in the fuel tank but nothing major - I've used injector cleaner (the one you put in the tank) but it didn't change anything.

I have no idea what can be the issue here so I hope you will give me some pointers as to what to look for.

Best,
Karol.

[wtdash]

Hi and Welcome from Poland!

-Did you replace the fuel FILTER?
- When was the CLUTCH done?
- Check your VACUUM lines - all those rubber hoses get brittle w/age and may be broken/cracked/etc.
- Spark PLUGS' age?
- Do you have 4 Fuel Injectors or some other type (USA Legacy's all have fuel injectors - I know other countries do not).

GL,
TD

[rallyak]

The coolant sensor might account for the hard to start issue when warm and that doesn't throw a code. Also could cause stumbling or jerking it also cheep to replace.

[karol1001]

@wtdash I've changed the fuel filter and plugs. Didn't look a the vacuum lines but I'll do that. The injectors are stock so 1 injector per cylinder.

@rallyak my fan comes on often so I also suspected the coolant sensor, but my temperature gauge always stays in the same position - no issues with overheating.

[rallyak]

Your gadge sensor is a different sensor, and you can test the coolant sensor with an ohm meter and see what it is when it's cold. I have to look in my book to see what it should be at a certain temperature. It could be reading a colder reading causing the engine to be too rich causing too much fuel when warm.

[karol1001]

Ok, so the sensor that might cause these problems is located on the intake, correct? On the side of the airbox. Where is the sensor responsible for the gauge inside the car?

If you might check the ohm measurments it would be great

[wtdash]

Hi,
Both sensors are on the cross-over pipe underneath the intake manifold - on the passenger side (on US car).

The gauge is just single wire connector; the CTS is an actual plug-in plastic connector.

But consider this caveat:

The above is true, the sensor may show resistance readings that are within the acceptable range but still can be out of proper calibration for the specific resistance/temp correlations that the ECU expects to see.

Google found this info for the CTS:
2.0 - 3.0 kohms @ 68 deg F
0.3 - 0.4 kohms @ 176 deg F

Td

[karol1001]

Wtdash, thanks a lot! I'll check it out.

You also asked about the clutch. Can it cause these symptoms? The car doesn't suffer from any other issues that may direct to a clutch problem. I never had any slip when starting from full stop and the pedal-feel is fine.

[wtdash]

I'm NOT a clutch expert, but 1st gear has very little torque on the clutch/trans (unless you do a clutch dump - which I don't recommend!).....

When my clutch went it would slip in 4th (and 5tH) gears when I would accelerate 'briskly'....in other words 'high torque load' situations. You can also test it, but I'll let you find that on- here/line.

TD

[CAV3MAN227]

-I'm going to have to look into this too!

-Joe

[rallyak]

What brand of plug wires? My wife's car I replaced the wires with three different brands and the NGK's worked the best. Her car would miss under load with the other wires.

[major_tom]

Also, I'd have a look at your engine mounts as well. I've been experiencing a similar jerk when going on/off the throttle at moderate RPMs due to my shitty mounts. The jerk comes from the engine reacting to the throttle but shaking while doing so, resulting in that shake being passed up the driveline.

Just my .02.

[dankberries]

The problem is only slight - the engine never dies and has no major issues starting (only sometimes when warm). It's just annoying because when I want to accelerate hard sometimes there is a delay in the power.

To answer if its clutch related , when you press on the accelerator do the RPMs go up but car does not accelerate forward? Or does the engine cut out and loose all power, takes no rpm gain?

Also , your symptoms don't occur when the engine is cold? Only when warm sometimes?

[karol1001]

I replaced the whole engine (now it's a 2.2 not a 2.0) and during that I changed the clutch to a new one (the whole shebang). The not-so-smooth acceleration from low RPM is still there. Can't figure it out...

[Legacy777]

So you have a new engine and new clutch and the same problem is still there?

The only thing left I can see is something drivetrain related.

[karol1001]

Josh, what should I check in the drivetrain? I believe the mount in my rear diff is shot, because I hear a knock when I rapidly let the cluch go after changing gear. Are there any other weak spots apart from the rear diff bushings?

I still tend to put the blame on an electrical issue so I already bought some wire to do the grounding mod. I wonder if that will make any difference but there is surely something wrong with it cause my lights go a little dim when the fan turns on.

[Legacy777]

Check out the diagrams in this link. You'll see some of the bushings for the various suspension points. The front diff or "outrigger" bushings are known to cause clunking.

http://rallispec.com/mou_bush_rstbk1.html

If you have the ability to jack up the car and go underneath to put your hands on some of the suspension components, it may help in finding the problem.