tstar

Recently installed some prototype Headers and each and every run (about 14) the AFR went to 19:1, pegged exactly at 4.2K RPMs. The Dyno Tech suspected he was getting some errant noise and attached an extra ground to the engine to no avail, although it did kill my TPMS. The car ran fine. I've never had this happen before...

Has anyone else had a simular problem?

lucky131969

Perhaps I'm misunderstanding. If the AFR gauge pegged at 19, which is already lean, it could have conceivably been higher(because the instrument can't go higher). Why did they continue to run on the dyno if the engine is leaning out?

tstar

The Tech was certain it was some form of errant noise messing his sensor up... The car was running great actually or at least felt like it was. And he was very knowlegdable, Bart Grande, you may know him? He's been on Monster Garage several times, NASCAR Mech ect...

Here's what he used Lucky, homemade;



I was just curious if anyone else has had anything like this happen as I plan ot go back for a tuning session and want to resolve this if at all possible.

Tim

lucky131969

Ok. I don't know the guy, and I'm not concerned with his resume... Although I do like monster garage....

It would freak me out to run on the dyno knowing the AFR was pegged lean.....even if the car seemed to run ok.

Try posting in the scan/tune section as well.

Hope you get it figured out....

vettenuts

How is your valve springs? Did you dyno before the new headers?

tstar

I ddin't run any compression checks but they weren't making any abnormal noise nor did I throw any codes, which is the first thing I checked when he told me about it after the second run on the baselines...

We ran about 7 or 8 runs with the old header system on, which had Dynoed well several years ago so I don't think there's any exhaust reversion ect. issues with the new system as the baseline and after install runs were all behaving exactly the same. Here's the old sheet;



I'll get in touch with him to see if he saved all the runs or remembers exactly what the AFR was doing prior to 4.2k, but I'm sure he said the AFR was fine until 4.2k then it just dropped out...

Sooo I take it no one else has had this happen before?

Tim

tstar

Yeah it's a fun show... he sid that it's even crazier then it depicts on the TV!

I'm setting up a tuning session for the Spring there and I want to make sure this doesn't happen again...

Tim

LoneStarFRC

That AF (if accurate) is ungodly lean! Have you had your injectors checked? Does he have any way to monitor your exhaust temps either during or immediately after a pull to see how high the temps are? That "window" of leaness is puzzling.

I agree with you. You need to get to the bottom of that issue. Keep us posted Tim.

Robert

tstar

It is odd that happened at exactly 4.2k isn't it??? I'll wait to hear from him to confirm where the ratio was at prior to running on air only!

Tim

99vetteran

When we dynoed mine it never went about 16 even at idle and actually went rich at about 5500 rpms. I'd also be concerned with the afr being that lean, was he also trying to tune it or were you just getting some numbers for the headers. From looking at where he placed the sensor that could be the problem. My Magnaflow exhaust is alway richer in the center tips as thats the mandrel bend that come out of the muffler, the other tip is always leaner and cleaner looking as its just welded to the mandrel bent pipe. You may be getting false readings from the sensor which is showing its lean. Look at your two tips and determine which is richer then the other and see if that could be the cause, my tuner said they always have more problems with the dual tips. To get the most accurate reading you need to have a bung welded on up front to hook it up correctly, you won't get false reading like you may be getting now.

tommie

the shop that did mine removed an o2 sensor and screwed in a wideband for their dyno... I asked about this, and they said that they always get false readings when just using a probe in the tailpipe...

Blow Torch

Tim

I think it would definitely be worth your while to have a O2 bung welded in right after your header so you can get a more accurate reading. The makeshift "sniffer" being that close to the mufflers (or resonators on the new system if it has them) might be some of the issue

Skinny Kid

I had this same problem with the wb in my Z. It ended up being a cracked sensor. I replaced it and no more problems.

Justin

Chevy Guy

I'll tell you right now, that car was NOT "running fine". The huge dips in the power correspond with the AFR freaking out. If I saw that graph just once, Id shut the test down.

tstar

I had one added to the system. ;



Lesson learned on tailpipe sniffers!!!! Thanx everyone for picking up on that!!! The outside tip is certaily always cleaner then the inside one, so that makes sense...

Tim

tstar

The Tech was certain it was the software reacting to the false AFR sensor readings... Certainly I would have felt a drop in power like depicted on the graph, expecially that mojo one at 5.1k!

BUT now you've got me worried!

Tim

Ikester

If the AFR was truely that high, wouldnt you hear massive pinging like marbles in a can?

tstar

I would certainly think so... but nothing. Car pulled strong till I let off at 6k. And I was on edge too because I've never driven on a Dyno before, freaked me out to be honest!

Tim

tstar

Update: The AFR was 12.8/9:1 consistantly until exactly 4.2K RPM then it shot to 19:1...

Tim

Chevy Guy

Good point, I would say definitely. Interesting that the guys didn't hear any. The plot thickens.........