Exhaust changes causes problems
 

I just replaced the stock exhaust with B&B and X pipe. The car seems to stumble in low rpm and hesitates a little during acceleration. The car acts like it wants to backfire, but doesn't. Any ideas?:pray

Re: Exhaust changes causes problems
 

Did you remove the factory cats?

Re: Exhaust changes causes problems
 

No. The factory cats are still in place.

Re: Exhaust changes causes problems
 

Hmm well if they were I would suggest a chip change however since they are not Im assuming a stock chip?

Re: Exhaust changes causes problems
 

I have a Chip from Marc Haibeck. It was tuned for a stock setup. Would an exhaust change like this require a reprograming? I figured I wouldn't need a reprogram until I put headers on it.

Re: Exhaust changes causes problems
 

I am getting ready to put headers on. Watson's I think. I have the Haibeck chip and am expecting to have to have it reprogrammed. I have heard I can expect backfiring without cats but that can be programmed out.

So far:
K&N with Open lid
Flowmaster Catback
Haibeck Chip

Once the headers are on (a couple weeks) I'll post the results.

Re: Exhaust changes causes problems
 

I would not think so with the cats one I would ask Marc if it is his chip

Re: Exhaust changes causes problems
 

I believe that mark pulls just a little fuel out of his base prom. . if you got the 3in bandb you could be running just alittle lean . are you using 91 or 93 oct fuel . also remember that this time of year they put more ethanol in the fuel this is a winter thing .

Re: Exhaust changes causes problems
 

also you might want to ck your fuel pressure to see if everything is ok . how long has it been since you changed your fuel filter ? hopes this helps

Re: Exhaust changes causes problems
 

Good idea. I just got the car back in July. How hard is it to change the fuel filter?:icon_scra

Re: Exhaust changes causes problems
 

20-25 min job flare wrenches make the job easier

Re: Exhaust changes causes problems
 

One thing to check as well is for exhaust leaks. Those will create some of the problems you are describing as well.

Re: Exhaust changes causes problems
 

Roger, the fuel filter is over on the frame rail on the right side next to that cat....well sort of next to the cat. Ya can't see it too clearly as there is a heat shield that hides most of it.

I usually do that when I do my season "get ready" so I have the car up on 4 stands, makes for one trip to do all my underside stuff. Anyway, one stand under the right front rail where it turns in should do it.
Remove gas cap.

bleed off any pressure at the front of the right fuel rail schrader valve with rag to catch fuel or if ya got a gauge with a bleed line your gold.

Use a catch basin under the filter anyway, or a rag. I always get some spillage.

Take off the two bolts that hold heat shield....mm, 10 or 13.

Using Line wrenchs on the filter and line 19 & 19 or 19 & 20 mm(?). Hold filter with one wrench and undo the line with the other wrench at "in" & "out".

Remove the filter band clamp bolt, 10mm & remove filter.

Reverse to install new filter. Leave car up and KOEO to test for leaks. Heat shield back on. Lower car.:wink:

Go for test drive, then have beer!:mrgreen:

:cheers:
Tom

Re: Exhaust changes causes problems
 

Good point !

Re: Exhaust changes causes problems
 

Jeffs got a good idea too. you might want to test for the exhaust leaks when you do the fuel filter. that is only if you jack the whole car up in the air with 4 jackstands under the car . do you have the zr1 bible (helms manual) they are just over a hundred bucks and very worth it . also worth considering is a scann tool to dk for codes that may pop up from time to time. congrats on your new ride . these are very special and cool rides:thumbsup:

Re: Exhaust changes causes problems
 

I appreciate everyone's help. I talk to Marc H today. He thinks it may be a sparkplug or ignition problem. He doesn't think that what is going on is a result of the new exhaust. Since I had recently changed the sparkplugs he said it might also be fuel related. He said to hook up a long hose and a gauge and drive it around to see what the fuel presure measures. If someone could give me an idea how to pull this off, I would like to try it. BTW I just drove the car for about 15 minutes and it didn't seem to hesitate as bad(then it started snowing). Don't know if this means anything or not. Looks like the fuel presure is as good a place as any to start. Please help.:pray

Re: Exhaust changes causes problems
 

roger,

When you say that it feels like it almost wants to backfire, what exactly do you mean by that? What is it doing? Can you be more specific?

Re: Exhaust changes causes problems
 

In talking with Marc, the backfire issue doesn't seem to be a problem. I am use to hearing the stock exhaust. He said what I was hearing had always been there, I just didn't hear it as bad. The real problem is that in low rpms the car seems to hesitate more and at WOT it was stumbling at around 4500 rpms. Once past that it was fine. It almost seems like maybe the engine isn't getting enough gas, I don't know. I feel stupid not being able to describe the situation better or know more about what is going on.

Re: Exhaust changes causes problems
 

What kind of plugs and where did you gap them?

Pete

Re: Exhaust changes causes problems
 

They were the recomended AC DELCO part. I can't remember the part number. The mechanic said they were the right ones. I also had a new spark plug wire set to put on the car, but the mechanic said the ones on the car where ok. I wish he had changed them, at least I would feel better about it knowing the wires were new.

Re: Exhaust changes causes problems
 

Roger,

Its possible that the less restrictive exhaust may have caused the AFR to lean out somewhat. Can you get a scantool on it? The 4500rpm region is where you might expect Knock Retard to come in and the hesitation could be the ECM pulling timing out.
Just possibilities which need to be verified by a scan.

Re: Exhaust changes causes problems
 

I am new to all this, I will see if any of the z guys around me have a scantool that might be willing to help. I just ordered the Helms manual, so that shows you I am little behind.

Re: Exhaust changes causes problems
 

you might want to invest in a setof ngk irridiums. i switched to them and just love em

Re: Exhaust changes causes problems
 

Hypertech makes a fuel gauge with a hose long enough you can gently shut the hood on it and still see the gauge while you drive. Screw one end on the shrader valve (make sure it dont leak) and watch the gauge under load.

Re: Exhaust changes causes problems
 

Thanks for the info. Sounds like something I can pull off. Where is the best place to buy a Hypertech fuel gauge? I have looked on line and can't find one for a 91 corvette.

Re: Exhaust changes causes problems
 

I think I bought mine from Mid America Motororks, Im sure there are cheaper places some of the guys know of but thats where I got mine.

Re: Exhaust changes causes problems
 

lazy 02 sensor.
New free flow exhaust, 02's are not warming up as fast or staying cool.

Just a guess.:wink:

Re: Exhaust changes causes problems
 

Correct me if i'm wrong,we have heated O2's and they are on the OE CAT/manifolds.

Also to run lean with CATS on i don't think that would be unless bad pump filter or injectors.
Our Z's run a bit rich from the factory around 12.6-12.8 AFR
I don't really think his running that lean to cause it with just an exhaust install since he also kept the CATS
Look at Marc H's web site on this.

Heck i ported the heck out of my intake,heads,63mmTB,headers,B&B's
X-pipe no/CATS and still didn't need to adjust fuel.

Pete

Re: Exhaust changes causes problems
 

Something else I didn't think too much about was the last couple of times I was letting the car warm up, it died. This has never happened before, but I just thought it was the cooler weather. The thing is it died after about 3 minutes. Could this be fuel related rather than cooler weather related?

Re: Exhaust changes causes problems
 

Sounds like primary fuel pump problem. When cold started, both the primary & secondary fuel pumps operate until the coolant temp reaches 167F, then the secondary pump shuts off.

You need to run the fuel pressure check described above.

Re: Exhaust changes causes problems
 

BINGO. i agree with the above . ebay has a real deal on fuel pump assemblies. but i remember in the bible it talking about one of the fuel pumps turning off as stated above . good catch :thumbsup:

Re: Exhaust changes causes problems
 

If it is a primary fuel pump, would I need to drive it to get the fuel presure or would it show the problem at idel. The reason I ask this is that I am having a hard time finding a fuel presure gauge that has a long enough hose to drive and check it.

Re: Exhaust changes causes problems
 

Try this first,hold both heater up & down arrow buttons for 5 seconds you will see 00 let them go and just hit the up arrow till you see 16 now hit auto button that will be your engine temp in celcius let your car idle till it hits 75 celcius if it dies then the primary pump is gone.
We have 2 pumps both are on at cold start up @ 169 F secondary shuts off.


Pete

Re: Exhaust changes causes problems
 

great explanation on how to use the airconditioner for temps i allways wondered how to do that =D>

Re: Exhaust changes causes problems
 

Well, all you really need to do is pull the secondary fuel pump fuse and keep a gauge on the rail and key on. Pump should run for about 2-3 seconds and pressure should be between 48-5 psi and hold after the pump stops running.

If you can find just a gauge, and hydraulic hose shop can build you a custom length hose.

Re: Exhaust changes causes problems
 

My way is the lazy way just sit back listen to tunes and have a beer.:p

Pete

Re: Exhaust changes causes problems
 

:sign10:

Re: Exhaust changes causes problems
 

I did what you said Pete(pretty cool btw). The car didn't shut off at 75. I decided to take it for a drive with the power key off. It drove like sh**. When I applied the gas, the car shuttered and vibrated for a couple of seconds then smoothed out. My question is even though the car didn't shut off at 75, can the primary fuel pump still not be preforming correctly. Just wanted to see if this rang a bell with anyone. I plan on getting a guage tomorrow and trying what Jeff said to do.

BTW I appreciate everyone's help trying to educate my ignorant a**.;)

Re: Exhaust changes causes problems
 

Roger,

Have you checked injectors?

Re: Exhaust changes causes problems
 

Injectors were all changed in August.