Shudder on Acceleration!

[jonbourg]

Ok, I got my van runnig after top end overhaul (see She's Runnin). I've only driven my van so far up to 40 mph. Van is a 2001 Silhouette 3400 SFI (now has a '98 intake). Was overheating, but I fixed that issue. It idles very well, but on acceleration has some shuddering/vibration and makes a low growling sound. Also seems to have slight power loss when this is happening. Any ideas what this could be?? Could one of the cylinders be misfiring? Could this be a pushrod in the wrong position (I'm still worried I got one wrong)? The service engine soon light is also coming on and it says change engine oil(brand new).

[david3100]

Epidemic? I have 3 doing this. I'm beginning to suspect gasoline blend. What part of the country are you in? I'm in middle TN. BTW- I hope you don't have Bosch spark plugs. That'll cause shudder.

[Z26-T]

Don't worry about the change engine oil light, that's because you didn't reset it. My bets are that you put a pushrod in the wrong location. You can also check for a vac leak to make sure that you didn't crack the intake, etc. Spray some brake cleaner (aerosal) around the intake. If the RPMs raise, that means you have a vac leak. If they don't... I would pull out the pushrods. My bets are you will have a bent one. If that's the case, 9/10 chance you bent a valve, so you'll have to pull the heads off and check them out. Pull the valve covers and let us know what you see.

[jonbourg]

I just got back from Autozone. Codes are 0202, Fuel injector (No 2 cylinder misfire) and 0135, 02 Sensor. Will have to wait till Friday to get parts. I'm pretty confident I got the pushrods correct now. Other than the slight shudder its running good and its not losing much power either. What do you guys think?

By the way, I installed NKG Iridium IX Spark Plugs.

http://www.ngksparkplugs.com/products/spark_plugs/iridiumix.asp

[IanSzgatti]

i think you contaminated your injector some how, and i also think you 02 sensor is contaminated... those two conditions definatey create the shudder and lack of power your talking about. As you accel, the mixture get's completely fucked, computer shits itself, and that's pretty much that.

I wrecked my ICM once with an arce between coils. Worst thing is I didnt know it happened. Took me about 20 minutes to realize.

I ordered an aftermarket ICM, and installed it in a 97 Lumina Sedan with 140,000 kilometers on it (90k miles?) that we had for sale on the lot here. I took THAT older stock GM ICM and put it into my car.
I learned quick from guys on this site that you can't go wrong with stock ICMs.

P.S. get some stock plugs.

[merlot566jka]

make sure you got the plug wires on all the way and that they arent arcing

check the connector at that injector

also check the orings on the lower intake if you pulled the injectors out. chances are that they were nice and swelled and stuck in there before and they either shrank, got nicked, or arent seated all the way.

while there is a posibility the o2 has been contaminated, i doubt thats the issue. it would make sense that the problem with #2 injector is causeing a lean or rich situation and thats why the o2 is throwing its self as a fault. just because there is a code for the o2 doesnt mean its faulty. it means its measuring something that it shouldnt, and it knows its not right. so it faults.

the easy way to check the oring on the #2 injector is to get some tb cleaner or carb spray with the straw attatched. while the engine is running, spray around the oring for the #2 injector. if its a vac leak, the rpms will rise and you may have found your problem.

to test that the injector is ok, youll need a test strobe light, while the car is running the light is tapped into the two wires on the injector and if it flashes, the injector is getting its needed input. from there you would move on to actually test the injector (or just grab a known good one and put it in there. and try again.

trouble shooting will save you much time and money. and heartache.

[jonbourg]

I went and got a new 02 sensor and started pulling everything apart. When I got to the fuel rail I pulled on #2 connector. Guess what! It came off! On further inspection one of the pins is corroded. I'll have to fix the wiring harness one way or another. I also pulled the plug and it looked good. Been sitting for almost a week so it was dry. I have the fuel rail o-rings, but not the injector tip end o-rings. I'll get some of those and replace all the o-rings before putting it back together. First I'll do a resistance check on the injectors. I'm not fully convinced the 02 sensor is contaminated, but it's got over 130K miles on it so I'm changing it. I think the corroded pin was causing the misfire and that set off the code for the 02 sensor as well.

[IanSzgatti]

130k is enough for an 02 sensor for sure! Nice to see you've made progress buddy, good shit!

[jonbourg]

It's Done!! Changed the 02 sensor and #2 fuel injector. I also ohmed out the wiring harness and all the injectors before putting it back together. She started right up and runs very nicely and the check engine soon light did not even come on. Also idles very steady. Thanks for all your help guys!!

[IanSzgatti]

yeah we'll all miss ya there jonbourg... might have only 15 posts but i feel like i've known ya for at least 186... good luck buddy

[IanSzgatti]

I'm beginning to suspect gasoline blend. What part of the country are you in?

interestingly, the Check Engine Light was designed to eliminate paranoid fears of mass conspiracy theory. just thought ya might like to know.

[jonbourg]

Thanks Man! I'll be around!