Surging between 42-48 mph

Jigg · Post by **Jigg** » Thu Jun 15, 2006 5:18 pm

My truck has started surging between 42-48 mph if i only give it partial throttle. I can power through it no problem, but if i'm trying to maintain that speed, it surges (RPMs, not tranny). A few weeks ago, my tailpipe rusted off at the muffler, and i haven't fixed it, i'm guessing this could be related to a lack of backpressure? Any ideas?

Thanks guys!

Post by **HenryJ** » Thu Jun 15, 2006 5:35 pm

Check the ignition components for the cause of the surge.
I tried the Bosch Platinum plus four plugs and developed a surge at cruise speeds. The rpms would jump a few hundred rpms. Sounds like a similar situation that you have.

The tail pipe rotting off can be several things.
The system needs to warm up to burn out the condensation that is formed. Pipe size and driving habits can play into the life of a system. If your pipe is big it may take a long time to heat up. If your commute is short there may not be enough time to warm up. You can try smaller pipe , but that comes with an increase in back pressure. Driving a longer time is not usually an option. The next is to use pipe that will last longer. Stainless steel is the choice for most systems, but it too can fail. I used 3" aluminized pipe. I do live in a desert climate though.

Back pressure should be unrelated to the rotting tail pipe, or at least I do not see a relationship, other than heating the system. In the tail pipe after the muffler, that should not be part of the equation.

F9K9 · Post by **F9K9** » Thu Jun 15, 2006 5:38 pm

Jigg,

Could you take the time to add the yr of your ZR2 to your profile? A model yr might help someone with a little knowledge. I know, I know, I won't be affected. I can't remember from "the Mother Ship" what you had but, I know, I had the problem in my '97 ZR2 similar to yours and SeaFoam corrected it.

Jigg · Post by **Jigg** » Thu Jun 15, 2006 5:39 pm

Thanks Brule!

Sorry, i was saying that the surging was related to the loss of backpressure (due to the pipe falling off)

I'm going to check out the cap and rotor, that's one thing i've been meaning to do and it's definitely ignition related.

Sorry Reed, it's a 2000 Blazer

Post by **HenryJ** » Thu Jun 15, 2006 6:33 pm

Reed is right about injectors causing a similar symptom. Make sure the ignition is in good shape then look there.

Be sure to heed the warnings about the plastic distributor. I hate to see a simple check wind up being a housing replacement $$$

Jigg · Post by **Jigg** » Thu Jun 15, 2006 6:36 pm

Sounds good. Thanks guys!

I actually had to replace the distributor on my last blazer (different reason, but i f-ed up that housing too). Not something i feel like doing again, so i'll be cleaning that threadlock as much as possible

Snoman002 · Post by **Snoman002** » Fri Jun 16, 2006 5:52 pm

How fast does the surging happen? Kinda of a slow rise and fall, or fairly rapidly?

I had more of a bucking happening with my 99 Bravada that was a tranny problem.

Try just VERY lightly touching the brake pedel when it happens and see if it goes away, touch it just light enough to turn the brake lights on, not enough to engage the brakes.

Just a thought.

Jigg · Post by **Jigg** » Sun Jun 18, 2006 4:50 am

yeah, it's not a quick surging/bucking like a tranny problem. It surges about 200 rpm, probably takes like a second or so for it to surge up, and then a second to surge down.

Jigg · Post by **Jigg** » Mon Jun 26, 2006 4:55 am

I put some 20gal techron concentrate in it. All better! I think you were right with the injectors Reed!

F9K9 · Post by **F9K9** » Mon Jun 26, 2006 11:35 am

Jigg wrote:I put some 20gal techron concentrate in it. All better! I think you were right with the injectors Reed!

Glad to hear it. The SeaFoam also freed up the float a little in my 97's fuel tank but, not much.