Hello Everyone, I am a new member to the site, although I've been reading topics on here for years. I recently bought my second blazer and I'm having some issues with it. The previous owner installed a Lunati mild street cam on it. When I bought it, it had a CEL light on. I pulled the code and it was for the O2 sensor as well as the code for the MAF sensor. I replaced the MAF sensor and the O2 Sensors. The MAF code disappeared, but the CEL is still on for the O2 sensor even though I replaced both of them in one shot. I also had to get a tune from PCM for less which made it idle better due to the street cam it has installed. I also did some routine maintenance on it, changed Spark plugs, wires, EGR Valve, IAC valve, PCV valve, Throttle body/Gasket ( previous owner tampered with the blade), MAP sensor. I am having an issue where the truck seems to lack power, idles rough, and it bogs while accelerating along with backfires. Any help would be greatly appreciated, Ive worked on these trucks for years since I also have a 96, but never had this type of issue.

 

backfiring where, exhaust or intake, intake backfires are messy and indicate either METRIC TONNES of unburned fuel in the cylinders still, meaning check your intake runners inside the plenum for washout from leaking fuel, pressure regulator, and make sure you're on an MPFI system, its a 1998 so you can upgrade. OR, since its had a cam swap check mechanical timing, to my knowledge these engines pretty much will not run unless they are on the mark but who knows. If its an Exhaust backfire its the same problem but less serious, check for washout, figure out why you have more fuel then you should being delivered, could be related to the tune and the cam not being quite matched up or it could be a wiring gremlin. Lots of routes to chase, check for vacuum leaks too, cap off the manifold ports if you must.

 

Thanks for the response, I apologize for not elaborating. It's an exhaust backfire. Before the tune it used to idle worse, It could actually be a fuel issue, but I was also thinking the oil pump may need to be replaced. Its got a slight tap, not sure if its a lifter tick or a broken manifold. Im going to check that soon.

 

Why replace the engine oil pump? are your pressures lower then 18-20PSI at idle when warm? and if so then by how much.

Anyways, may want to see if PCMforLess can give you more info on your tune, pull your fuel trims too and post them up, need both banks Long term and Short term.

 

I was thinking the engine oil pump due to fluctuations in the psi. I know that 18-20 PSI is considered normal, but it tends to idle like trash once it reaches normal operating temp. I have already reached out to PCMforless. I will keep everyone posted.

 

thats pretty normal, my rig does that when its just warmed up and the engine RPM is inconsistent, the oil pressure gauge seems to be better then the tach at telling what the engine is doing at idle.