Ok, here is a new one. After almost a 1,000 mile trip, after the last fuel stop before I came home. All of a sudden on my acceleration to get back on the interstate, I hear this hissing that increases with throttle input. Also seems like there is a drop in power. It sounds like it’s coming from behind the seat! It idles fine, no code, low speed is fine, but as soon as I get on it past about 1/2 throttle, or if it is under a load like going up hill, the hissing starts and increases with the throttle input. It feels/sounds just like a turbo leak on a big turbo diesel! Except it is just a stock ‘91 5.7 Tbi with a 5- speed, regular cab, short bed. I know the fuel tank is just below and behind the cab. Could it be the evap. system is leaking on top of the fuel tank? Exhaust leak? I would think an exhaust leak would just be loud and not a hiss. I dunno, anybody heard of this? Thanks.
Vacuum or air leak?
- Thread starter bowtie-72
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
Thats an odd one. The only time ive heard a really loud hissing noise like that was when my old distributor slipped and it was absolutely fire hosing fuel through the throttle body.
It was actually pretty loud.
The only other thing I can think of is that your fuel filter is right below your seat on the frame rail but I kinda doubt thats it.
It would think that a fuel leak loud enough to hear it would make it run like crap all the time.
Does it only do it while you are driving?
Doesnt really seem like an exhaust leak.
And I dont think an exhaust leak would cause the performance problems you describe
It was actually pretty loud.
The only other thing I can think of is that your fuel filter is right below your seat on the frame rail but I kinda doubt thats it.
It would think that a fuel leak loud enough to hear it would make it run like crap all the time.
Does it only do it while you are driving?
Doesnt really seem like an exhaust leak.
And I dont think an exhaust leak would cause the performance problems you describe
Plugged catalytic converter. That is, a cat that's too plugged for heavy throttle, but not so plugged (yet) that low-speed is noticeably affected.
Had those exact symptoms on an 03 Trailblazer halfway between California and Home. Cost me hundreds of dollars in a small town in the middle of nowhere--they didn't have a replacement cat, had to order it, and I had to buy a hotel room for SWMBO and I until the replacement cat showed up and could get welded-in.
I replaced the O2 sensor when I got home.
Had those exact symptoms on an 03 Trailblazer halfway between California and Home. Cost me hundreds of dollars in a small town in the middle of nowhere--they didn't have a replacement cat, had to order it, and I had to buy a hotel room for SWMBO and I until the replacement cat showed up and could get welded-in.
I replaced the O2 sensor when I got home.
That’s what I was thinking as a possibility, a clogged cat. I never had one go bad before. It only has 150,000 miles on it, but it is 30 years old so anything is possible. Seems odd that it just started after my last fuel stop, but that could be just a coincidence. That’s why I thought it may be the evap system. I thought maybe the venting fuel from filling the tank may have ruptured a 30 year old hose. I was going to try to plug the vacuum line at the vapor canister as a diagnostic to see if it would stop. But as you accelerate, vacuum would actually decrease so that doesn’t make sense. This is a constant symptom as the load increases on the truck.
If you still have the old pellet style cat, you'd wanna replace it anyway with a high flow one.
Probably, but we don’t have any emissions or safety inspections here. I would be more inclined just to drain it out and hollow it out. But my guess is that the O2 sensor would sniff that out and set a CEL. I could drain the contents into a coffee can and take it to a scrap yard and make a couple of bucks off of the “repair”. LOL
Not really, you only have one O2 sensor which is in the left side exhaust manifold. It doesn't care about anything downstream. I just like the idea of being somewhat Eco conscious plus, it'll reduce the smell of your exhaust. Here's what I have, bought it in 08/18
https://www.amazon.com/Thunderbolt-...83-8-2-141--&vehicleName=1988+Chevrolet+C1500
A new cat is $60--$80. Add another twenty for a couple of band-clamps, or for someone to weld it in place. Might as well fix this right. We all have to breathe.
Speaking of which..."I" would not want to be anywhere near the old pellets and the dust/debris you're going to be releasing without a respirator. Tens or hundreds of thousands of miles of fuel residue is not something I want inside my lungs.
Speaking of which..."I" would not want to be anywhere near the old pellets and the dust/debris you're going to be releasing without a respirator. Tens or hundreds of thousands of miles of fuel residue is not something I want inside my lungs.
Thanks for the heads up. I will take this into consideration. I thought new cats were priced much higher. I hear about the crackheads that try to steal them all the time to sell.
