Rough Idle/Hesitation/Backfire

[ittlfly]

The numbers for resistance look good. But you seem to have a problem under load. That's why I would still suspect the coil(s).

[flyin ryan]

Not saying this is it, but if this was happening when I'm on the dyno, first thing I'd check would be the timing...sounds like the timing is too far retarded? Do you have any idea what your base timing is, by chance?

[Gary Yarbrough]

I have no idea what the base timing is. I have notes on the car from about 25K miles and nothing to suggest that the camshafts have been retimed. However, I can't say for sure...

Now, I have a slight coolant leak. I had a chevy dealer replace the radiator about 2 months ago, so I'm a bit surprised. The leak is coming from somewhere near the bottom of the radiator. So, I spent my pulling the radiator shroud. I'm going to try to find the leak tomorrow when the sun is back out. I figure I should do the leak first and then the hesitation...

[flyin ryan]

Originally Posted by Gary Yarbrough

I have no idea what the base timing is. I have notes on the car from about 25K miles and nothing to suggest that the camshafts have been retimed. However, I can't say for sure...

I'm just talking about the 'Base' ignition timing at this point, Gary. Not the 'Cam' timing, of coarse depending where one or more cams are in at, it could be that also...? For now I would concentrate on the basics.

[Gary Yarbrough]

I'm not sure about the "base" ignition timing. I'm not even sure how to find out.

For now, fixing the hesitation is on "hold" because my radiator failed. About 8 weeks ago, I had a local GM dealer put on a new radiator. It seems that the new radiator has failed at the lower passengers side seam where the side tank connects to the aluminum. I've pulled it and am waiting for confirmation that it was a manufacturing defect. Then, I'll take a week or so for them to get another replacement...

[Gary Yarbrough]

I got my radiator and will be installing it by Saturday, so I'm back to trouble shooting the hesitation. While the car is drained of coolant, I took the opportunity to remove the plenum this morning. I'll be checking everything this afternoon/tomorrow.

My dad also convinced me to take a closer look at my MAP sensor. I noticed something that I need some opinions on. I'll try my best to describe this. Using a flashlight, I took a look inside the hole where the hose connects on the bottom of the sensor. While it was clean inside, I noticed that at the bottom of the hole, it appears to me that there is a small piece missing in the plastic. It looks as if I can see inside the sensor to some electronics. Since I don't know how the sensor is supposed to look, I suppose this could be normal, but the hole is irregularly shaped. Does it sound like I need a new MAP sensor?

[XfireZ51]

Originally Posted by Gary Yarbrough

I got my radiator and will be installing it by Saturday, so I'm back to trouble shooting the hesitation. While the car is drained of coolant, I took the opportunity to remove the plenum this morning. I'll be checking everything this afternoon/tomorrow.

My dad also convinced me to take a closer look at my MAP sensor. I noticed something that I need some opinions on. I'll try my best to describe this. Using a flashlight, I took a look inside the hole where the hose connects on the bottom of the sensor. While it was clean inside, I noticed that at the bottom of the hole, it appears to me that there is a small piece missing in the plastic. It looks as if I can see inside the sensor to some electronics. Since I don't know how the sensor is supposed to look, I suppose this could be normal, but the hole is irregularly shaped. Does it sound like I need a new MAP sensor?

If you are describing a vacuum connection that isn't sealed, then you need a new sensor. Trying to envision what you are describing.

[Gary Yarbrough]

I think that's what I'm describing. Let me try to do better. If the connector for the hose were a glass (let's say), then the missing piece would be in the bottom of the glass, not the sides. So, it is sealed in the sense that the hose is making a seal. It is just an issue of whether there should be a hole at the bottom or not.

[jeasen]

I had the same problem a couple of weeks ago with my ZR1. I found that I had water in my gas. Add some gas dry to your gas tank to see if this fixes the problem before you embark on a much harder and costly fix.

I think this is going to be a common problem now that the gas stations are charging more for premium fuel. The price for premium is no longer 20 cents more than regular and people are not buying it like they use to. Therefore the gas stations do not have the turn over like they use to have and I think we will see more water in the gas problems.

I hope this helps.
Jeasen

[Z51JEFF]

Ive heard nothing possitive about the Accel coils so if you havent replaced the plenum yet I would replace those coils.As far as the slapping noise,a miss will get the DM flywheel jumpin around and just might get the cam chains to make a racket.When I had an injector die I got a noise that sounded like a rod knock but knew it was the flywheel.