I just bought a blazer.
Its a '99 4x4 with the Vin W 4.3 v6.

I got it for $500, the only problem is a misfire. The truck as a whole has been kept maintained (has new trans, transfer case, hub bearings, u-joints, and brakes all within I'd say 20k miles from how it sits now).

It has 250K on the ODO.

The misfire is on the #4 hole.

My mechanic and I are trying to get a grasp on what the problem might be before we go tearing into the motor at all.

We have tried:
New plugs/wires/cap/rotor
Compression test (all cyls good, i believe 150? i dont remember)
Fuel pressure test, shows good
OBD scan, no codes (except #4 misfire) --The computer shows a miss-history for cyl 6 as well, but currently its only #4 missing.
Spark and "stress" spark tests for #4 hole, good
We did other things as well (EGR, PCV, etc -- but these all seem like they would effect more than 1 hole).

After running the motor if you pull the plug it is wet with fuel.

We swapped the plugs from #2 and #4, no changes.

we swapped wires from 2 and 4, no changes (#2 shows healthy at all times)

I am beginning to think its a Fuel leak, but why would it only foul cyl #4?

There is a lifter tick on the passenger side of the motor, but not a very loud one by any means.

I have been reading for a while, and It seems that there are a few parts to the injection system on this motor that like to fail, but I still cant wrap my head around it only effecting 1 hole.

Im trying to keep the costs down as much as possible, I will buy any part necessary to fix this, but because the truck is up there in miles, I dont want to just open the wallet and dump cash into it.

I know there is an MPFI Upgrade to this motor, but If Its avoidable, I would like to not have to purchase it. The truck in reality does not need to last that long, maybe a year or so.

Please let me know if you have any thoughts on this, all the other threads I have been reading havent been specific to 1 cyl (if it was a fuel issue) and were fixed by doing something we already tried (short of looking at the poppets, etc).

 

It has poppet nozzles, those are notorious for going bad. If you don't want to dump the cash for the multiport conversion, you can just buy a single poppet nozzle injector and see if that rectifies the situation.

 

What brand and part number of spark plugs are you using?

Check fuel pressure and leakdown. If leakdown is excessive, I'd suspect #4 injector is stuck open. If leakdown is within specs, I'd go for an AC Delco distributor cap and rotor, (don't forget to put silicone dielectric grease on all of the terminals).

Key on, engine off, fuel pump running, fuel pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the pump shuts off.

 

The plugs cap and rotor are all OE replacements. (unless im going for power, like with my LN2 turbo build, i ONLY replace with OE parts, im **** like that)

I dont remember the results of the fuel pressure test, but he is going to administer it again to check it.

Im thinking it is a poppet nozzle, which would be great! its only a $70 part.

Are there any "telltale" signs that a poppet is "going" bad if you look at it at all?

He told me the cost on the MPFI upgrade for him to get it is only $250, which i can live with if its really the cause of this problem. then again if there is no way to tell if the poppets are going bad, i might just replace the one (if its no good). Its easy enough to get in there and do the work and all.

again, this truck only has to last for a year, maybe 2 at the most, and all the other major expensive stuff has been serviced, repaired, or replaced already .

Thoughts on doing the one poppet versus the upgrade given the miles (if thats indeed the problem)?

Im new to the 4.3. I've worked on the GM 3.8, and im building a turbo 2.2, and ive done a few 5.7's, so bare with me lol.

I wont have any updates on the progress for a week or 2, my mechanic is slammed with other cars in front of mine, and I dont have any time (or a garage) to work on it.

I appreciate the input so far!

Thanks!

 

No sence throwing money at it needlessly. Proper diagnosis will find the problem. Fuel leakdown test will tell if the system is holding pressure. If not, it would be possible that a poppet is leaking, along with many other possibilities. If it fails the leakdown test, it only tells you there is a leak... somewhere. Further diagnosis is necessary to determine where. Key on, engine off, fuel pump running, fuel pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the pump shuts off, (GM factory procedure & spec). Harbor Freight has an el cheapo fuel pressure tester for under $20. Not professional equipment by any stretch of the imagination, but it works. Test takes about 10 minutes to do.

 

My mech is actually going to be doing all the work now, and will
be performing that test.

I'm not going to just start dumping parts into it, all I'm saying is it would be great if it
was a cheap/easy fix like that.

I will post up and let you guys know what it was when we finally pull it in his garage.

Thanks!