Help with 98 Chevy 5.7 misfire not running right

also to add, i was getting a p300 misfire and a p122 tps sensor code. thought it had a bad sensor thats why i replaced it. sensor code hasnt come back yet but just did that this morning and still messing around with it. could i have a bad spider injector causing the low fuel pressure?

What's the battery and alto stir like? If one or the other is bad it may not be getting enough voltage.

I have a 98 1500 with 5.7. Have same issue. I have replaced everything I can think of and still misfiring. My next move is to replace timing chain. Hopefully that'll fix it. Did you ever figure out your problem?

i had the same problem. i then took it to a shop and they emptied my gas out of my tank, put new gas in, then it worked fine. they told me not to get gas anymore from places with old tanks.

I have the same problem did you find out what was wrong.

Exhaust obstuction?

do a compression check on that cylinder if it is anything less than 110 its probably the valves for that cylinder, but to make sure do a leak down test too.

I have a 99 suburban showing cylinder six is dead but i am getting fire from distributor to plug but cylinder is dead any explanation for this

Ttt

I had same problem 97 5.7 vortec. Replaced cam and crank sensors repaired wiring to crank sensor, much better. I put it on co. Outer and it said can and crank sensors were not in sync with eachother adjusted timing got it down to 2 degrees, it can be - 2 or +2 but no more than 2

Mine is doing the same thing to I replace my spider injector cap and rotor and spark plugs with AC Delco spark plugs and my wires and it still doing the same thing but not as bad And mine had a lot of carbon buildup

Carbon buildup

My only option is the next change the ignition coil and the whole distributor

Old fuel injectors

And I’m still getting a p0300 I’m about done with this truck

99 Suburban, 194,000. Check engine light on for several months, my bad. Ran like crap suddenly, duh. White smoke from tailpipe, smelt of burnt paper. Did pcv, added fuel injector/ carb cleaner two tanks. Improved somewhat, decided to change plugs and wires ( code said #4 cylinder not firing ) Discovered coolant low, very old ( my bad) Flushed & refilled and new thermostat. Running great, but check engine still on. Old oem muffler was rattling at idle for months but still quiet while driving so I put it off. Finally got new aftermarket muffler installed, went out on freeway anf pedal to the metal. Olay! Check engine gone. So after all the above (shame on me) the last fix of the new lighter muffler did it.No more exhaust obstruction.

Oh, with new coolant, added a stop leak to the radiator, white smoke disappeared almost instantly. That was 1000 miles ago. No gasket change done. Hope this helps the original question of hard starts, poor idling: muffler obstruction was impeding idle issue.

Want through this with my 99 Tahoe with the 5.7. hooked my scanner up to and noticed I had a o2 sensor reading low, but not enough to set the cell off. Replaced all 4 o2 sensors and made it a whole different truck.

Went through this with my 99 Tahoe with the 5.7. hooked my scanner up to and noticed I had a o2 sensor reading low, but not enough to set the cell off. Replaced all 4 o2 sensors and made it a whole different truck.

I got same problem with my 96 GMC 5.7 vortec been workin on it about a year I have changed so many things NOTHING works same problem,I just drive it now and then.My classic 1964 nova ss with a 377 cid and No computer runs great.Bobby Howell bobjh010@yahoo.com Thanks

to all who are having a miss fire or lack of power under load replace your fuel press. regauler under the upper intake on the spider injector i had the same prom. for over a year i have been a GM tech for over 20 years i didn't thor parts at it took time to thank that was my prom. and it runs like new now

Did you find out why only 50psi at idle? Mine is doing the exact same thing. Replaced fuel pump. Fuel filter. Spider injector assembly. Tps. Iacv. All 4 o2 sensors. Wires. Plugs. Distributor. Crankshaft position sensor. Cleaned egr valve. Still running rough. Code p0300. Random misfire. Key on truck off. 60 psi. Running. 50 psi. What in the fuck man.... Help me Jesus. With key on amps are reading low on gauge and secondary battery is not as strong as primary battery.

Yes I’m having same problem I have a 1997 Chevy k1500 5.7 vortec I put be MPFI, new fuel pump,new fuel line and filter,new MAF Sensor ,clean gas tank when installing fuel pump.new plugs wires cap and rotor.one morning when it was cold I went to start truck and i wouldn’t fire up.i then replaced fuel pump filter and line and it did start Drove it around block but kept falling in its face and sputtering and lack of power.i then put new multi port fuel injectors in and gaskets and it seems to be worse.the service engine light is flashing and it sounds like it’s not running on all cylinders.i Havnt done fuel pressure check as no don’t have gauge but just holding to hear some feed back .im think of doing cat delete and installing new 02 sensors

Just looking if anyone has anymore info on what’s going on with their vehicles I have 99 5.7 Burban doing everything of the above and I have changed out everything and still get codes 0339,0339 0102,0507,etc starts fine isles at 900rpm fixed wiring at crank did away with that 0300 code motor tranny have 80,000 crate motor just different things keep popping up ecm maybe ???

I have a 99 Tahoe with all the listed codes on this page . the Fix is replace your fuel presser regulator . this will fix the miss fire the lack of power when towing or under havey load it took me a year to find the problem with OUT replacing parts this is the fix i been a GM tech for over 20 years its not in any book or well know . the fuel press. reg. is under your upper intake on the side of the spider injector $20 part.

I have a 2005 Chevy Silverado 4.3 liter V6 changed ecm, distributor,cap,wires,plugs,coil,fuel pump assembly and still getting code p0300, and injector circuit,etc. So whoever is giving advice on the problems YOUR FULL OF CERTIFIED SHIT. PULLING OUT THE JUNK AND GOING BACK WITH OLD SCHOOL 350 MOTOR AND TRANS

Have a 97 2500 chevy van, had the same problem. Would not run right. Missing out bad. Replaced everything I could think of. Finally it sent a code. Crank position sensor. Runs great

Have 1999 tahoe 5.7 runs great other than when under load or heavy acceleration. Replaced distributor replaced fuel filter plugs wires cleaned maf sensor still same problem. Trying fuel pressure reg. Next any advise would be appreciated

I have a 1998 Chevy K1500 5.7 Vortec that ran perfect with no engine codes, it has 140k on truck, my intake starting leaking, no oil in water or water in oil, it happened at my house so truck temp never got above half way, I replaced the lower intake gasket and put everything back together, I marked my distributor but I think it’s out of time, I know with the Vortec engines you HAVE TO HAVE A SCAN TOOL IN ORDER TO GET THE CAM RETARD SET BETWEEN -.02 to +.02, could I have set my distributor wrong??? The only code it’s giving is a PO300, it has no power on the highway and misses badly, if the truck is out of time with it give a po300 code????

You don't have to have a scan tool to set the distributor. Look online, there is some articles where you have the crank position on TDC and the mark on the tab on the timing cover. There is a number under the rotor bug on the distributor. Line it up and when it seats into the oil pump it'll be timed. I didn't have a tech 2 and did this and it worked. No codes and runs strong. Just use google, there is a good article somewhere. This below is it I think. http://www.gmtruckcentral.com/articles/distributor.html

My Tahoe 1998 Chevy Vortec 5.7 had the same problem at everybody saying and my Cadillac converter with clogged one of them got the Cadillac converter off put a straight pipe and it runs perfect now so all you people that saying you have misfires check your Cadillac converters I bet you any money the clogged

Sorry wrong photo

Good thing you didn't load up the nudy photos, this would have went from a auto site to porn in a new york second

https://www.youtube.com/watch?v=YT2UO9Rg-ig watch 18:50 - 20:00. a default bank fire would cause all of these problems including slightly lower fuel pressure. also my experience with these is bad grounds both body and circuit due to age. the wires get brittle then melt to each other. the ground intermittently jumps into other circuits. plus when your body grounds are bad the communication is poor between the modules, check pid data for irregular waveforms.

Check your ground straps (body to frame and engine to frame) replace if needed, check the cap and rotor for corrosion or burn thru change if needed, clean or change mass airflow sensor and pigtail...... I have a 1999 Chevy Tahoe 5.7L vortec that had the same issues, I did just what I listed and my problems went away