I have a '96 T10 Blazer w/ 4.3 - 155,000 miles

I bought it last summer here in Arkansas and drove it to Nova Scotia, Canada and back with no problems. Since it's gotten colder here though I came up with a dead #1 cylinder when the engine is cold (and even until I drive 20-30 miles).

I start it at 5AM to go the 28 miles to work and it runs on 5 slugs the whole way. When I leave work at 3PM it runs perfect from the start all the way home. I get a flashing SES when it's running bad that reads "Misfire #1 and O2 sensor problem" (presumably from unburned gasses in the exhaust).

I replaced the fuel filter, all vacuum lines, cap, rotor, wires and plugs. (BTW, I hate the (#3) middle plug on the drivers side :-) I replaced the #1 wire and plug again just to be sure, checked all the connections I could find and it's still the same.
Throttle position or RPMs make no difference at all to this problem, if it wants to run well it will. There are no fuel, or any other smells or sounds that go with it, just a solid dead lope. The SES light goes solid as soon as #1 starts firing when the engine is hot (again, never before 20 miles if it's cold out) and goes off completely the next time the truck is started.

When the cylinder decides to work it fires on - and - off in spurts for a few minutes before it's all the way better, then it's fine all day until next time it's cold.

Thanks in advance for any insight here... I can't afford to replace all kinds of things just to try it. I have a new coil sitting on the bench but it's unopened and I'll return it if I need something else.

Carl.

 

i'm not sure if the '96 4.3 is CPI, if it isn't it's possible you're dealing with a clogged injector. have you tried running a couple of bottles of fuel injector cleaner through or checked the injector wiring?

 

I checked the wiring for the injectors, I was thinking they would be more of a constant issue than temp. related. I'll throw a bottle of cleaner in this weekend though... Can't hurt!

O'Reilly auto priced the injector "spider" at over $300! hopefuly I won't need that!

 

Possible that you have a sticking poppet valve. Run some Chevron w/ Techron through it. You can get 2 12oz bottles for the price of 1 at Advanced Auto. I would run it in the next 3 tanks and see how it goes.

Another area to check is that the spark plug boots are actually connected and not working their way off of the distributor cap terminals. If you used dielectric grease, trapped air in the boot could cause them to work their way off of the terminals and cause your misfire. I ran around this problem on my Bravada right after a tuneup. My solution was to use an ice pick I have in my tool box while I push on the boot. This allows the air to escape while you push it onto the terminal.

Check all of your wires on the cap this way.

Also, did you check the gap on the plugs before you put them in?

If the coil were bad, I would think it would be all over the place as far as the mis-fire code is concerned...

 

so the '96 4.3 is MPI? the CPI engines have problems with leaky fuel delivery/return lines, but i'd think that would present itself as a misfire on more than one cylinder (and hard starting, too).

are you getting spark at cylinder #1 when it's misfiring?

 

'96-'02 or '03 are all SCFI. I believe it was mid year '02 that they switched to the MPI with injectors at the end of the spyder tubes where the poppet valves are in the SCFI.

If the plug is not firing, it should be wet from unburnt fuel.

 

excuse my ignorance, but what is SCFI? i was of the understanding that my '97 4.3 was MPI.

do you mean CSFI?

 

MPI = Multi Point Injection which technically speaking, the SCFI is.

SCFI = Sequential Central Fuel Injection. (or is it CSFI = Central Sequential Fuel Injection... one of those...)

The difference between what I would call MPI and our SCFI is that MPI typically has the individual injectors pointing directly at the intake valve. While the SCFI (in our case) has all 6 individual injectors in a centrally located injector pack. Tubes then direct the fuel down to poppet valves (mechanically actuated by the opening of the electronic injectors and the subsequent fuel pressure increase in the tubes) that point at the intake valve.

There is a retrofit that can be done to update the SCFI unit to a true MPI unit. I would only advise doing this in the event that something is wrong with your injector spyder as it is quite costly. If you are contemplating replacing your injection spyder, let me know. I think I posted the PNs somewhere awhile back...

*EDIT* - I thought I would also add the main difference between the CPI and SCFI systems. The CPI system uses ONE centrally located fuel injector which then pressurizes 6 tubes running down to poppet valves. This system batch fires the main injector. In the SCFI, the injectors are fired in the optimum time for their respective cylinders.

 

Mine has the one injector for six tubes. I did check the spark plug boots on both ends for being in place very well and have re-checked them several times.
The #1 plug is dry after running bad, even looks about the right color funny enough.... I am getting the O2 code, which I was attributing to a load of fuel / air mix in the exhaust each cycle of the engine, but it could just be air if the fuel isn't getting in there.

The injector spider is sounding more likely now.... But why just when it's cold out? Perhaps too lean a shot to ignite with dense air??

Magtec, thanks for the reminder... I still didn't get around to checking for a spark on that cylinder. The engine is always warm enough to run well when I get home..... I did check the gaps on the plugs when I installed them though.

I'll run the Techron through and let you guys know what happens in about 14 days :-)

Does anyone know how much the $tealer charges to pressure clean the injectors with - um - Nitrogen I think?

Thanks for the help so far!!!!