Added the weight of ONE person, jerking is back!
 

I earlier had some problem with my blazer jerking at steady speed around 45mph/1500rpm. I can't tell you what I did to make it go away, as I kept trowing parts at it all last summer.

Usually there is only me, my wife and the dog, today my father also was with us and the jerking was back. Dropped my father off and drove home, the jerking was gone.

Why would the adding of one persons weight make the jerking come back?

sounds like something is wrong with your suspension. did you replace the shocks? is your rear end sagging?

I feels more like a transmission or engine problem. New shocks and no sagging :)
Thought it was my lock up solenoid, but that should not go away with less weight.

how many miles do you have on your blazer? is it the original transmission?

118060 miles with original transmission :)

sounds like the engine is skipping

Thats something I never heard of before. Could you explain?
If it only would pop a code, but there is no codes.

have you done a tune up recently?
replaced the injector unit?

I have changed just about everything, plugs, wires, coil, air, fuel and oil filter.
But not the CPI unit.

Do the RPMs fluctuate during the jerking? If you give it gas while it's jerking, does it seem to respond well?

I can't say that I have noticed the rpm fluctuate during the jerking, but if I give it more throttle the jerking goes away. It only jerks at steady cruising speed at 1500 to maybe 2000 rpm. It feels like if you tap the brakes one time very quickly.

Next time you experience the issue, tap the brake to unlock the torque converter. See if the jerking goes away. 45MPH is about the speed where the torque converter will lock up in OD (4th gear).

Its just that, when it jerks, it does it only one time, 1-2 minutes later one more jerk. Never several jerks. I have read some post on this and they say to do the same thing, but I can't get it to work with only 1 jerk at a time.

I have ordered the fuel system parts that I mentioned in my last thread, but not recived them yet, maybe this could be part of the same problem?

TC shutter would be persistent, not once in a while.

Sounds like a misfire to me, but that should be throwing a code. Also, the weight thing doesn't make sense for that problem being a misfire.

The added weight may just make the symptom more pronounced. I know I had a slight, intermittent miss in my old 2000 Bravada that I never really did find the ultimate cure for. It was most pronounced when the A/C compressor would engage while cruising down the road, but that was not the only time I would experience it.

Things I have changed since late summer 2009:

Two O2 sensors, EGR valve, TPS Sensor, ICV, FPR, Fuel pump, Plenum gasket, LIM gasket, ECT Sensor, MAP Sensor, Thermostat, spark plugs, wires, cap, rotor, Catalytic Converter, muffler, Coil

But as stated earlier in my posts, new parts arn't always good parts!

There shouldn't under ANY circumstances be arcing from the spark wires right?
I took a spray bottle with some water, put it on mist and sprayed some of the ignition parts. At the #2 spark plug there was arcing between the engine and just above the wire cap. The thing that makes me question this is if I used to much water, would it arc no matter what?

You should not have any spark escaping the wire jacket. That is a lost spark.

Could this cause the jerking?

Depends on how pronounced the jerking is. A misfire can definitely be characterized as a jerk.

It's like a very quick and light tap on the brakes. But shouldn't a misfire throw a code? Maybe not when it's only intermittent? And it get worse when the engine heats up.

a misfire should through a code, yes. When you turn your car to the accessory position, does the SES light come on at first? I've heard of people buying used cars where someone pulled that bulb.

I'm not sure how long you've had it, but it's always a possibility.

Since you've recently changed the wires, did you use good quality ones or a crap brand? It could have been defective. It'd be worth pulling the wire and reseating it, just to make sure it's on really good.

An intermittent misfire may not satisfy the conditions required for the P030x family of codes to set.

SES light comes on with key at prestart position yes. I used AC Delco wires. Wires are seated all the way and routed to not touch eachother and the surrounding stuff.

it's only 1 wire that is causing a problem, right? If you have your old wires, try switching that 1 back to see if that makes a difference.

The new wire could be bad....

Rechecked them tonight, again with a spray bottle. I get these sparks/arcings from several wires. Also at the coil and the wire between the coil and the distributor.
But I can't see them without the mist of water.

Did the test even one more time and there are arcing all over the place.
That makes me think that the wires maybe are OK, but that I got a different problem, that makes them arc.

Any developments on this? I am having a very similar issue.

I have still not found the problem :icon_doh:

Not to threadjack, but I think we have a similar situation here, and may be able to help each other out even though the vehicles are slightly different..............

I too have put on lots of parts and labored over this motor: Delco wires, Delco platinum plugs, Accel coil and module, new pickup coil, "free flowing" cat, Dynomax catback, fuel filter, all new vacuum lines, intake gaskets when I pulled the intake to clean the EGR passage in the head/intake/solenoid, a couple oil changes with Mobil 1, a couple nice doses of Seafoam, fuel pressure checked out good in all conditions, etc. It runs well until it warms up, but then misses at very light throttle pressures, especially before shifts.

I just got done pulling the plugs and the #4 plug was mostly fouled. I rechecked all my wire routing, added some insulator and whatnot to the plug wires and all dist/coil wiring, and it still does it. Going to try an Accel cap and rotor next I suppose.

I'm at my wits' end with this blazer and it's engine!
Feels as if I have tried and changed everything, but no luck!
compression is good, after new fuel pump and spider fuel pressure is fine, ignition is fine. So I don't know what to try next. But as you wrote, it gets worse when it gets warm/hot.

Have a look at my other thread, might me something to this:

https://blazerforum.com/forum/engine-transmission-35/problem-95%25-gone-two-days-%25-%A4-45039/

I have the same problem. is 45 mph at a shift point for the motor or something?

I saw that other thread and have been thinking about that; I can't put much logic as to why that would make a difference, but was thinking of putting a breather type filter on that valve cover anyhow. I'll let ya know.

I put a "high perf" Accel cap and rotor on last night and covered every inch of plug and coil wiring in fresh insulator. It helped in all areas except where the miss occurs of course.

Another thing I have been thinking of is about how my #4 cyl is the one where the most issue is according to the plugs.....this is also the cyl with the EGR port from the head. This could possibly mean the EGR solenoid is acting irratically, but that would normally throw a code even with OBD 1.

I'm going to start checking grounds, ground/power wires, and connections at the ECU today.

Also, my ABS light came on recently and I have no codes which leads me to believe I have a grounding issue somewhere.

Best of luck to ya; keep throwing ideas out there and hopefully someone can track this issue down.

I don't know what engine you have, but if its the cpi unit it could be a leak at your FPR or spider just above the #4 cyl. Slow dripping fuel down the cyl that makes a missfire.

Did some more troubleshooting today. I used a stetoskop and put it to the fuel tank. Even now with a new fuel pump I can hear the pitch go up and down togheter with the eratic idle. But what I don't know is if the idle affects the pump or the pump the idle.

I also put the stetoskop to the fuel filter and there I heard a sound best described as a fast "TIKKATIKKATIKKATIKKATIKKATIKKA", this sound gets faster with higher idle. I can't imagine what woul cause this sound to come from the fuel filter. I know its the fuel filter and nothing else.
I tracked this sound all the way along the fuel line to the test port on the back of the engine. The sound was not as loud at the engine, but its clear that this sound follows the fuel lines from the filter.

Checked the spark plugs again today, they where like new!
That takes a fuel leak off the table, right?

What you are likely hearing at the fuel filter is the injectors opening and closing. It makes sense (to me) that it would be louder at the filter given it's larger area for the stethoscope to hit against. The sound is actually caused by a pressure wave that shoots back down the fuel line as each injector closes off. This phenomenon is called "water hammer".

As far as plugs ruling out a fuel leak, they may, but the definitive proof would be a fuel pressure test...

I have a fuel leak some where, that I'm almost sure of. But with the plugs looking brand new, I don't think it's at the CPI. After shut off the psi still jumps up to 60, 10 minutes later the psi has dropped to 10. There is noe external leaks, so that leaves the tank and the spider. The fuel pump setup is new, togheter with the tank, the CPI is also new. One of these has to be leaking right? Hope I don't have recived bad parts one more time. This would make that the third time this year.

The most recent symptoms are small "PUFFS" comming from the exhaust at idle. Soot around the exhaust tip and still some surging at take off and acceleration. The jerking is also still there, but not so much as before.

Isolate the pump by installing the gauge at the filter. If the pressure still drops, the check valve in the pump is bad. If it holds steady, then you have a leak inside the plenum.

From your descriptions of the exhaust, you have a leak inside the engine still.

When you replaced the spider, did you also replace the 'nut kit' (internal lines)?