'96 4.3L S-10, misfires or hesitates at constant speed

[j cAT]

Originally Posted by bigmak5996

ty fish i will do that this weekend will let you know how it works out

getting the codes is a good idea before spending money on other items. what you did so far is just routine maintenace. these items need periodic replacing before you have problems. on replacing these items inspection of the wire resistance plug color cut open fuel filter checking for restrictions etc arcing inside the cap. all this helps you to determine whats going on.

items that can be defective are the oil pressure fuel switch and the ICM. with the age of this vehicle these components are in most cases not working correctly. often these items are ignored as the engine performance slowly suffers.

[theo715]

The same problem on my 98 4.3L s10 the code is random missfire and Ive changed to a AC/Delco, new wires and plugs and still does this. No cat smells or anything. So im thinking maybe a bad enjector on a cylinder or something?

[copdills]

my 98 s10 is doing the same thing random misfires when checked runs great as long as you give it gas , but I have noticed when I fill my gas tank up it runs great until I get back to 3/4 full and it starts missing again at constant highway speed and the ses light comes back on , I can drive 30-50 more miles light ses light goes out runs good for another 50 miles or so and starts missing again at constant highway speed , Thanks for any replies

[Blue Bowtie]

Have you retrieved the DTCs? That will remove a lot of guesswork.

There is a chance the EVAP system has a problem. My '96 Sonoma also generated P0440 codes with a partial tank. Replacement of the purge valve on the EVAP canister and several vacuum lines solved it.

[21sprint]

Got a 1997 with same problem. !st off changed wires, plugs, cap and rotor with AC DELCO parts. Still same problem. Checked fuel pressure with key on 65 lbs and driving 55lbs. Tried a rebuilt Distributor, another set of wires, plugs and cap and rotor. plus a new EGR valve, MAP senor and MAF sensor. The truck seems to run better with EGR unhooked. I replaced intake gasket(it was bad) and thought I had it, no. I just replace both upstream 02 sensors now and no help. This truck sort of falls on it's face and bucks and jerks, only codes in missfire and EGR pintle.I watch my computor and it shows missfires on every cyl. but never says if one cyl. is the problem. I wonder if the pump is not really putting the volume to injectors. I've went way to far on this truck to stop now. I can't beleive it's the pump though, it starts fast and holds fuel pressure for 30 minutes after I turn key off.

[copdills]

I can fill mine up with gas and it doesn't miss for about 80-100 miles, I had it tuned up 7 months ago with orginal parts my mechanic told me it might be my gas gap, replaced that no luck if I fine my problem I will let you know , please do the same for me with yours , I hope you het your truck running right , I bought mine new and would like to get it fixed
thanks Randy Dills copdills

[Tech II]

It's not really rocket science.....

If you do not have access to a scan tool that can pinpoint which cylinder is misfiring, first thing is check spark output at the end of each ignition wire with a spark tester......

An old trick is to cut small pieces of washer fluid hose, and insert them between the wire and the distributor......this hose is high in carbon.......now with the car running, take a test light, ground it, and then touch each piece coming out of the distributor.....this kills a cylinder......now, if you kill a cylinder, and rpms drop you know that circuit is firing.....if there is no difference, then you've found your bad cylinder......if you have good spark at the end of the line with a spark tester, and compression is good, it's leading towards an injector....those spider assemblies were known to have stuck poppet valves, that caused misfires......

With CPI, there is one injector and the whole assembly has to be replaced....the next generation was CSFI, with 6 individual injectors, so the whole unit did not have to be replaced, only the bad injector......Second generation uses a MAF sensor......make absolutely sure there are no air leaks between the MAF and the intake.....

[21sprint]

I'm using a old Snap On computor and mine shows missfires jumping around, new Spider injection and new rebuilt distribtor didn't help, This truck feels like its losing power when you hold it down and when you back off a little it just starts surging badly if you hold it in that position.

[Tech II]

Cat could be plugged....

[j cAT]

Originally Posted by 21sprint

I'm using a old Snap On computor and mine shows missfires jumping around, new Spider injection and new rebuilt distribtor didn't help, This truck feels like its losing power when you hold it down and when you back off a little it just starts surging badly if you hold it in that position.

remove the upstream O2 sensor .if with the hole open and the engine is running better then the exhaust is restricted.

[21sprint]

Originally Posted by j cAT

remove the upstream O2 sensor .if with the hole open and the engine is running better then the exhaust is restricted.

Cat was stopped up. I've never had a truck nor car act like this one, but that was the problem.Thanks

[j cAT]

Originally Posted by 21sprint

Cat was stopped up. I've never had a truck nor car act like this one, but that was the problem.Thanks

hopefully the unburned fuel issue was fixed. this is what normally cause the cat converter to get damaged/plugged.

the O2 sensor removal trick is a well known fast way to determine the issues you have .. your vehicles operation is 90% of what the restricted exhaust would do ..

good luck ...

[snakeongrass]

i had this problem (jerking on freeway at constant speed). if there is no engine light on..the problem is more then likely your crank shaftsensor.rightunder harmonic balancer.. this fixed my problem for two years. i am having this same problem two years later . this timeit isnot the sensor. inow have a transmission code..it can be either one ..snakeongrass

[snakeongrass]

hey i just found this .. i think its my spacer for crankshaft sensor this time ..https://www.youtube.com/watch?v=KLC0E7N47Lw
if you dont get link . there is a youtube video talking about needing a spacer for new crankshaft sensors.. i am 99% sure you guys have a crankshaft sensor out.i have replaced one years ago for same symptom in the same truck .. this guy says that chevrolet has made a notic about needing shims. snakeongrass