hello everyone here is my problem i have a 1999 4 door blazer 4.3 motor i replaced the spider injectors, the fuel pump, the throttle body, the distributor cap and rotor the spark plugs, the wires, i hollowed the converter due to no emissions here in our part of pa, i replaced the air filter, the fuel filter and now heres the strange part i put my hand over the air intake and choke it out, it runs great but when i take my hand away once it gets to 3000 rpms it bogs down and it wont go over 40mph up hill, i am going crazy what else can cause this? please help thanks in advance!

 

Sounds like a vacuum leak. But gutting the Cat was a waste of a good converter. These trucks run better with the cat than without them. What you should of done IMHO is removed the muffler & left the Cat. Or installed a straight through muffler as I did. You will find that by gutting the Cat you will loose low end torque badly, & most likely see "Check Engine Lights" often if not all the time. Not to mention loose gas mileage. I'm always amazed that auto manufactures spend Billions of dollars on R&D to get vehicles to perform in all perimeters of driving to get max fuel mileage & performance. Then people without any engineering think they can improve their vehicle by doing as you have done. I'm a retired OLD mechanic that worked with top racing people in my day. The work that went into getting vehicles to perform at their peak in just ONE area was always a challenge. If you ever noticed ENGINEERS are what NASCAR & INDY teams employ more than anything else.

 

thank you for your reply, i hollowed the converter because it raddled around all the time it was'nt like there was no problems with the converter, i think you may be right about the vaccum line but i can't find anything leaking? i was going to change the distibutor and the computer next but someone said that it could be the mass flow sensor but i have no idea where that is on this vehicle?

 

ive never had to deal with this, but some guys on here have talked about the intake tube becoming soft and collapsing when the engine is under load. just an idea...

 

thanks for the reply checked that already its good, do you think it can be the cpu?

 

i dont think so, seems like you would have a alot of other problems. mass airflow sensor sounds more logical to me but i am a novice. its easy to do. be sure to get Mass Air Flow Sensor cleaner. heres a how to https://blazerforum.com/forum/article-submissions-discussions-47/how-maf-sensor-cleaning-discussion-thread-18620/

 

i will try that, it is really strange that if i hold my hand over the tube while it tries to suck air in, it runs great, i take my hand away and it runs bad like its getting to much air?

 

sounds like you have a leak or something is sucking air thats not supposed to. try another intake or buy a cheap cold air kit and see if that remedies it.

 

No Service engine light? It almost sounds like the EGR is stuck open or commanding too much at higher RPMs

Out of all that, I only get the check engine light. Truck runs better. Still get around 17.8 mpg out of every single tank doing 70/30 city/hwy driving. Didn't lose low end torque, either. Running a 2.5" Dynomax catback w/ no cat at all. Just a straight pipe.

And then went and ran a 15.88 with a 2.2 60 ft with 170k miles and 80psi compression on one cyl.