I'm having a rather frustrating problem. I've got a 86 s-10 blazer, 2.8 TBI. It runs beautifully when I first start it up and will do so for as long as 30 or 45 minutes if I just leave it on the driveway running, but after a while it begins to stumble and want to stall out, and it will backfire into the throttle body. If I start it and take off it may run great for a few miles and then it starts stalling and misfiring and backfiring into the t.b. In some cases it will do that for miles, in one case it stalled out completely and refused to start stranding me. So far I've been chasing my tail with this issue. I thought initially it might be a clogged fuel filter, so I changed it out, but it had no effect. At times it will stall out and won't start back for a while. I checked and am definitely getting good fire to the plugs, and I can also see both of the injectors spraying what looks to be the normal amount of fuel that I usually see them spraying. However, once it hits this no start condition it simply will not start unless I let it sit for a while, despite getting fire and fuel. Even checked the timing, which was a bit out, and after sorting it out it does run much smoother when it's running. Sometimes after it begins to stumble and backfire it will do it for a few minutes and then begin running great again. It's very intermittent and quite frustrating. In the process of working out another issue, I've also replaced the ICM and the ECM, but they've also had no effect on this particular issue. I'm starting to run out of ideas short of just randomly replacing stuff, but that's not the proper solution. I'd really appreciate any ideas on this!

Thanks in advance

 

Ahh, I also removed the EGR and inspected it, but it didn't appear to be that dirty and didn't appear clogged, though there was some carbon buildup. Also checked the diaphram and it didn't seem to be broken at all.

 

Update: I checked out the TPI per a suggestion from another forum. I did find that it was out of adjustment (was reading about .32v) so I tweaked it a bit up to about .43v. It's still doing the same thing however. It started acting up just a few short minutes after making the adjustments. Then it ran perfectly for about 20 minutes and then started stumbling and backfiring into the throttle body again.

ACK!

 

Well, though I've gotten 0 replies for this problem, I'm going to go ahead and post the resolution in case it can helps someone in the future.

Basically, I've been chasing this issue for the last week or 2. After much troubleshooting and trying to hit the simple stuff first, I completed a fuel tank replacement a couple of days ago and went ahead and replaced the fuel filter again as well for good measure (replacing the fuel filter was one of the first things I did trying to troubleshoot this problem) and everything is working wonderfully thus far. I went ahead and upgraded it to the 20 gallon tank and replaced the sender/float assembly as well, so it's all brand new except for the pump (which, despite processing the bad gas for a few weeks, is still a fairly new and unused AC Delco pump). Took it for a spin around town last night for about 30 or 45 mins with no problems, and then drove it into work this morning also with no problems. It's running better than ever (not surprisingly). In the process of troubleshooting this mess, I've adjusted the timing, tweaked on the TPS adjustment, revamped my vacuum system, tightened belts, replaced the PCV valve, cleaned the EGR valve, etc etc. and it's all showing now that I can drive it around again.

The sock filter that's attached to the intake side of the fuel pump was so caked up with rust it was unbelievable. Once it dried out I had chunks of rust flaking off of it that was at least a 1/2" or more thick. In hindsight, it's amazing this thing was running at all. The interesting thing is, for the most part my injectors were still always firing into the throttle body even when it wouldn't start or would begin to run badly, so that just goes to show how much the volatility of the gas was being affected.

The installation of the new tank went fairly well, except for a minor snag here or there, mostly having to do with going from a 13 gallon to a 20 gallon tank. The tanks were dimensionally almost identical, but the only real issue we encountered was when trying to adjust the straps that route above the tank to increase the vertical space for the slightly-taller 20 gallon tank. There is a bolt for each upper-strap accessible between the top of the bumper and the body on either side of the license plate that is to be loosened as-needed. Unfortunately the bolts were so rusted up and caked with crap that it was almost impossible to loosen them enough. Despite using penetrating oil and whatnot, I still broke a bolt on the drivers side upper strap, so I just went ahead and broke off the one on the other side as well so I could get the tank on. As it happens, there was still barely enough clearance to get the bottom straps mounted on and the top is pushed well into the body on the topside, so I don't anticipate any play that would cause the tank to bounce around. It was nice and snug. After a day or 2 of driving I'll get back under the truck and try to jockey the tank back and forth to ensure that there is no play. Also, I'm going to let this fuel filter catch any rust left behind in the fuel system for a month or 2 and then change it out again to try and remove as much as possible from circulation.

So, that's that.

 

Thanks for the info...I'm sure it will help out someone down the road, that's what these forums are all about, passing on the tricks and tips we all learn the hard way. Good luck with your ride.

 

hmm i have a 91 4.3 doing the same dam thing and i have also played round especialy with mat sensors and o2 sensors and i had the gas tank fuel sender and lines all replaced brand new i have yet to mess round with the vacum stuff but i think im gonna check out that filter on the fuel pump so thanks for the info

 

Can you tell me if you have any images or advice on getting fuel filter back into bracket on 86 S10 Blazer w small v6 ( 2 wd)
Thanks

 

I relocated my filter on my 86 to the drivers fender well. Much easier to change now.
Steve

 

Any suggestions on getting stock location back in? Do you have a pic you could email me? Our sons blazer not running too well, so have removed stock filter and got replacement ( stock replacement )

 

Are you working on it with FSM? If so is there a site you can refer me to to dl a fsm pdf for 86 2 wd blazer also v6 ( 5 sp )??

Thanks for all the great info you posted, I am new to this forum and hope you can direct or guide me to information please