Blazer -98 jerking

[Jari]

I have -98 Blazer 4.3l W. It has started to jerk when it's cold. First it jerked when cruising at steady speed, now it jerks also when accelerating.
What I've done so far:
-total tuneup a year ago
-cleaned MAF
-cleaned and checked EGR
I guess to be done is to check fuel line pressure? It starts very well though. Check catalytic converter?
Should I use fuel injector cleaner? Could this be a injector related problem?
What else should I check?

[G.A.S.]

One of the problems with this engine is that the distributor cap gets moisture in it. It is a known problem with no recall that I know of.
Remove the cap and see if you find moisture inside.
Fuel filter is another good one, I would replace that before doing a fuel pressure test as you could get a false reading.
On my blazer I used dilectric paste at the base of the cap where it sits on the distributor and havent had any moisture problems sence.
just a couple thoughts

[Jari]

ok , just bought fuel filter. have to check distributor, thanks, I'll let you know..

[Jari]

Fuel filter replaced. Distributor checked. Fuel line pressure checked. But still jerking. Any other ideas?

[DelCoch]

Is the SES light coming on? If not, does it come on with the key on and the engine off?

What all did the tune up include that you did last year? What band name parts were used? Some of the aftermarket stuff is junk.

What is the fuel pressure reading and how long does it hold before it leaks down? How far does it leak down?

[Jari]

SES light comes on when ign is on motor not running and is not on when engine is running.
I rebuilt the engine. It was driven without oil. New distributor cap, plugs. I didn't change plug wires anyhow. They may be next in my list?? I sprayed water over the cap and wires in the dark when idling, no visible sparks anywhere.
All parts I used were AC delco and other quality brands.
Pressure is 61psi when pump runs, after that stays 57-58psi.
Jerking happens usually when I cruise steady speed above 100km/h (60miles/h), when accelerating no problem.
How can I test TSP? could this be a problem with it? I noticed that problem usually occurs when 2200-2400rpm, bad potentiometer???

[DelCoch]

How can I test TSP?

Do you mean the Throttle Position Sensor? I would suspect the spark plug wires before the TPS. When plug wires get old they develop high resistance and may do fine supplying high voltage at full throttle, but don't do so good with low voltage, like at an idle.

Fuel pressure sounds good. I would go ahead and replace the plug wires, no doubt they are probably due and then you can be rule them out. Go with the A/C Delco on the plug wires also.

Let us know how it goes.

[Jari]

changed spark plug wires. didn't help. it jerks now only when I'm cruising steady speed over 100km/h. Could it be catalytic converter? It does accelerate ok though. Transmission related problem? Any other ideas?

[534BC]

http://www.automotiveforums.com/vbul...d.php?t=607221

Pg 4 finally has my solution. I would concentrate real hard on when and why it is jerking, if you find it is at mid-high rpm and light - lighest load then conclude that it is missing at the highest timing advance and/or the leanest mix.

[Jari]

Originally Posted by 534BC

http://www.automotiveforums.com/vbul...d.php?t=607221

Pg 4 finally has my solution. I would concentrate real hard on when and why it is jerking, if you find it is at mid-high rpm and light - lighest load then conclude that it is missing at the highest timing advance and/or the leanest mix.

Thanks 534BC,
I think it's jerking when mix is leanest. It usually does this when i have been driven for 10-15 min highway (engine warmed up) and going downhill. I have AC-delco plugs and new wires.
What was your solution? Distributor bushings?

[534BC]

http://www.automotiveforums.com/vbul...1&postcount=65

My solution is a "patch" but it still runs perfect. If yours is the same you would notice it at the exact moment it goes to closed loop AND very light throttle.

[Jari]

Now it does it all the time... Even when accelerating..
Plugs, wires, etc changed. What next? Any ideas?

[Jari]

Took it to the dealer. They diagnosed it. No problem found.
I've started to suspect that the problem is TCC solenoid in tranny...

[aleekat]

Originally Posted by Jari

Took it to the dealer. They diagnosed it. No problem found.
I've started to suspect that the problem is TCC solenoid in tranny...

How old is the tranny fluid and filter??

[Jari]

Never changed I guess. I will change those and tcc solenoid this weekend, maybe that helps...