One Backfire then Stumble and surge issues

[ingrammc]

I started My 98 with a 5.7 liter Engine. soon after Startup the Engine Backfired and then began stumbling and Surging. It runs better but the RPM's are elevated when I disconnect the MAF sensor. I replaced the MAF Sensor but that did not fix the problem. it also stops stumbling and surging when driving normally I would say RPM's over 1500. so something that is affected by the MAF and only working during IDLE is somehow malfunctioning... I just don't know what that thing is. I have seen a lot of similar issues but none exactly like I am experiencing. I have also not seen any actual ends to discussions that result in it being solved.

 

[Frank Enstein]

Perhaps a leaky fuel injector.

Doesn't effect as much at higher engine speeds because the extra fuel is a smaller percentage of the fuel used at higher rpm.

Try a Berryman's B12 Chemtool and a Redline Si-1 fuel system cleaner. Run those through a tank of fuel and see where you are after.
The Berryman's cleans with solvents and the Redline cleans with detergents

Walmart and Autozone have the Berryman's and Summit has the Redline.

Red Line Synthetic Oil 60103 Red Line SI-1 Complete Fuel System Cleaner | Summit Racing

Free Shipping - Red Line SI-1 Complete Fuel System Cleaner with qualifying orders of $109. Shop Fuel System Additives at Summit Racing.

www.summitracing.com

 

[TreeGeared]

Anytime I have seen backfiring it is one of two things. Excess fuel in the exhaust (leaking injector maybe) or timing (cam or crank sensor, but should throw code). Do you have a scan tool that you can look at the 02 sensor reading or any codes?

 

[Schurkey]

Connect scan tool, look at the data stream.

Verify fuel pressure including the ability of the system to hold pressure after shutdown.

 

[ingrammc]

thanks going to get the chemicals and run them through a tank of gas because i still need to use the truck. while i am at the parts store i will have them scan it and get the codes. had it done once but forgot the codes

 

[Schurkey]

Codes can be useful.

Better to study the data stream--and they're not going to do that at the parts store.

 

[Frank Enstein]

thanks going to get the chemicals and run them through a tank of gas because i still need to use the truck. while i am at the parts store i will have them scan it and get the codes. had it done once but forgot the codes

I like to alternate them. One or the other every oil change and alternate between.

I would still do the double whammy the first time due to the suspected leaky injector.

 

[ingrammc]

So only code was P1701 the suggestion the parts store computer gave me was to change my intake Manifold Gasket.... Not going to do that. looking for vacuum leaks on or leading to the intake Manifold. then moving on to fuel air ratios. would replacing the Fuel filter help that? I am probably going to do that anyway. then there is the ever popular Oxygen sensor, does that come up with every code? Already replace MAF sensor. Could use any suggestions if my train of thought is flawed. I am also going to keep running the Chemicals in the gas. I will keep everyone updated on my progress.

 

[ingrammc]

I am an Idiot,

Found the exhaust leak in under a minute. A vacuum hose was completely disconnected from the intake manifold. Simply plugged it back in and the truck was running great again. I should have seen it, right on top, however I was concentrating on the passenger side of the vehicle where the Air intake box and MAF sensor where. As soon as I moved to look at the engine as a whole it stood out on the top of the engine Intake manifold on the driver side. I am just wondering if the hose somehow came loose or if the pressure from the backfire may have blown it off...