1999 4.3 misfiring

gmoncrief
0

Asked by gmoncrief Jan 05, 2009 at 12:22 PM about the 1999 Chevrolet S-10 2 Dr STD Standard Cab LB

Question type: Maintenance & Repair

I'm running out of ideas on a problem with my 99 S10 4.3
The truck will start and idle fine however as soon as you feed a little gas it starts to miss.
Giving it even more gas is either covering up the misfire or it is clearing and seeems to run better.
I've just replaced cap/rotor wires and plugs.
The problem seems to get worse whenever it gets even slightly wet/humid.
I had Cragen hookup a analyzer and it gave a "random misfire" error code.

Does anyone have an idea of where to look?
Thanks Greg
gmoncrief@hotmail.com

15 Answers

Michael McGrail
5,705

I would look at replacing your coil, moisture will commonly mess them up if they have a crack in them. If the coil is going out, the more you require from it, the more the engine will miss. It would create the code given. That would be my best educated guess from the information you gave.

1 out of 1 people think this is helpful.
Danny Wang
2,665

Just as a possibility I may also suggest trying a MAF cleanner, it should be about $8 a can. If it improve significantly, then I recommend replacing the MAF. Even though the frequency could be operating within specification, if it does not change as quickly as load on the engine changes, the engine may not be able to fire at the right time.

1 out of 1 people think this is helpful.
Jeremy Prchlik
45

your problem is a bad throttle position sensor, i had the exact sme problem, changed everything out but that sensor and it finally stopped doin that once i replaced the TPS. same exact conditions, whebn it got humid or after a rain it ran like shit lol

3 out of 3 people think this is helpful.
chevyfan88
0

I have this same problem with my 99 s10 4.3. the code reader says miss fire cylinder #2... so I replaced wires, plugs, distributer cap and rotor. after 2 days this problem got worse. again I read the codes and it read the same code, cylinder #2. good old GM I guess

FRANKENTRUCK
20

I know this an old thread, but seen alot of questions across these forums while searching for an answer to problem that seems to be irritating all of us 4.3 vortec owners. "The dreaded mystery coldstart misfire." I like many others had the shudder between 1500-1800 rpms until the engine came up to operating temperature. I just found the root of all evil hiding under the EGR valve. Removed EGR to clean and realized there was a blow by in the gasket. Removed gasket and noticed it was on the topside and underside of the gasket. Scraped the remainder off, cleaned the surface, and installed new gasket with original EGR valve. Instant success! I can see why people got rid of the issue when replacing spider injector because they probably removed and reinstalled new gasket when replacing EGR. Less than an $2.00 fix compared to the $300.00 cost of new injectors.(I still need to replace injectors as mine has over 300,000 miles on original but thats another project) Also remedied some annoying valve chatter. Worked for me...hope this information helps others!

2 out of 2 people think this is helpful.
wmdg
0

I have a ? I have a 99 s10 blazer that is doing the same thing. idels great but misses bad when taking of even when your going about 65mph it wil wanna miss and jump. punch it down and runs great. and cheap fixes possible? Id sure appreciate any info

FRANKENTRUCK
20

Have you checked your EGR gasket? I would start there.

wmdg
0

On a 99 where is its location? I've been told by several that is typical for the 4.3. Egr valve

FRANKENTRUCK
20

Its on the front of the intake. When you raise the hood, its a smaller cylindrical part with a plug with two wires I think. Two bolts and it lifts right off. You will need to have replacement gasket, scrape and clean old gasket off, blow carbon out of EGR and replace. Maybe a 10-15 minute job

wmdg
0

I sure appreciate it. i hope that solves it.

FRANKENTRUCK
20

I hope it fixes your problem. Please let me know. Thanks

wmdg
0

Does the gasket on egr valve require rtv?

FRANKENTRUCK
20

No rtv. It is a graphite gasket

wmdg
0

I cleaned the egr very well and the plunger worked good and did have carbon but not bad. put new gasket and still same problem . idels good and ribs up good. misses taking off and in neutral about half throttle it misses. put the coal to it and just fine until you plain off and it goes to jumping . I'm looking for the nxt remedy?

FRANKENTRUCK
20

I should have asked earlier. Is your check engine light on or have you been able to get any codes?

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