hey guys, short time member first time poster, but here it goes

(unimportant back story part

i saw a 98 chevy blazer ( it's a 4 door 4 wheel drive LS version btw) on craigslist and thought it might be decent so we drove on down there and looked it over. the origional ad said 2100$. when we got there it started and idled fine, but when we took it for a test drive, it barely made it around the block. it sputtered and backfired at any throttle past about 1/6th of the pedal travel. the seller acted suprised when it barely made it back, we believed him at the time, he said he hadnt run it in a little while. so i jumped on it for 1000$

(end unimportant story part


we towed it back home and tried to start it up, it started and idled, but way rough, we shut it down and wiggled the distributor and it seemed to run beter.(it seems to run better when you shut it off for a litle while then start it back up, but doesnt last very long) we figured it was just worn, the points were kinda square and we replaced it with a new cap and rotor the next day. it ran great when it was cold, but when it warmed up, to normal operating temp, it still idled just fine but it started acting up when you floored it, first at about 4500 rpm, then at 4000 rpm, so on till you couldnt drive it because all you can pretty much do was idle it back home,(we just took it around the block). since we have borrowed my uncle's obdII reader it came back with a couple of codes about a MAP sensor low input, so we hooked up a multimeter to it and checked it according to the haynes auto manual. was giving some funky readings so we replaced it,we erased that code, but then we got some codes for the MAF (low input again), we took it apart and cleaned it and it looked all right, we put it back together and it didnt come up with any more codes. we already checked that the lines going to all the before mentioned sensors and they were all steady at 5 volts through running cold and good or hot and crappy

all the things we have done: replaced the fuel filter, distributor cap and rotor. checked the fuel pressure and that was in line and didnt drop too quickly after key was off. put new good gas in it (figured it might have been a bad gas issue) checked the spark plugs, no fouled out ones, all looked good. put a spark checker dealie on the #1 spark plug and it didnt look like it was missing or anything.

when we started working on it we looked underneath and the cat converter was taken out and a straight pipe welded in, we figured this guy that sold it knew about the problem and tried a couple of things first. also the fuel filter looked new, but we figured, meh its cheep and that might be the bad piece in this puzzle.

if i've missed anything, im sorry but ill fill it in and take any advice at all, im just anxious to get this beautiful truck on the road.

thanks for looking and reading,

brian

 

I am surprised that you are not getting a catalyst efficiency code. The previous owner may have put in an O2 sensor spoof or had the PCM edited to remove the B1S3 codes. You may want to consider installing a replacement catalytic converter

Have you monitored fuel pressure while you are experiencing the drop in power?

Does the drop in power seem heat related? If so, it could be the ICM heating up, which could cause it to malfunction.

 

we tried a couple things like unplugging the o2 sensors and it came up with low input code on the o2 sensors we have monitored the fuel pressure and it falls in the parameters of the Haynes repair manual scale (don't have it with me right now). about the icm heating up, if you shut it down and start it back up it runs for probably 30 seconds with ok throttle response but then it starts acting up again.i guess it could be the problem still right? thanks for your help on this problem, i have seen a couple other bogging problems on this forum and they all seem to be a little different. it would be nice that there is a universal fix for the problem. btw the icm is the thing with the heatsink on it right? mines next to the coil on my engine.

thanks again,

brian

 

hey guys, great news my dad read somewhere that it might be the MAF sensor and we followed the advice of unplugging it when the engine was off and started it up. we drove it a good 5 or 6 miles with absolutely no problems. accelerated perfectly. no backfires or anything.

thanks for your help, swartlkk, and thanks to the great blazer forum for allowing me to post my problem.

thanks all,

brian

 

Before you go and plunk down the $$$ for a new one, try cleaning it.

 

i sprayed the old one that was on it with contact cleaner, it looked like it was pulled from a junkyard cause there was yellow numbers scribbled on it.

it didn't fix the problem completely, however, we were pretty sure that we had fixed the problem, but i got about 3/5ths of the way to work (about 3.5 miles) and it started acting up again backfiring and loss of power, we got it back home using the ol' slip it into neutral, shut it down and restart it, then back to drive.

we thought it might be the fuel pump. it kind of makes sense that this fixes the problem cause it kinda sends a slug of gas down the line. we decided to run it after work and check the fuel pressure again and we noticed that there were air bubbles in the gas line. we figued it was the fuel pump had a air leak or something in it and was forcing air down the line. i know that that if there were a hole in the fuel line it would spray gas outta the line and not bring air in, but is there any way that there is a leak inside the tank, above the level of gas?

i lowered the spare down and the lines looked new on the fuel pump. we think it might be worth it to take down the tank and look at the fuel pump. see if it is a decent name brand one. all the autozones near me carry are "airtex" brand, never heard of it. a lot of people suggested like an ac delco pump. we might check it this weekend or maybe tomorrow if this tropical storm clears up in my area.

thanks for the help

brian

 

try to replace fuel pump, i had same problem: it was worn out fuel pump

 

hi guys, thanks for your help, it was the fuel pump. aparently it was pumping enough volume but it was falling within the pressure guidelines. when we plugged in my uncle's fuel pressure checker, it said it was the right pressure. but when we hit the release pressure button when KOEO the engine would die. we replaed the fuel pump and it didnt die when we pressed the button.

thanks all

brian