My '94 Blazer (W) has had a slight miss under load the last couple weeks. I decided to do a tune-up since it was due. I bought it last year with 140,000 miles on it and now it's up to 163,000. The previous owner had used Bosch Platinum plugs (yuck!) and cheap wires. The Bosch plugs were covered in crud when I pulled them out. I was surprised they even fired they were so crusty!

I ordered all AC Delco parts from Rock Auto and put them in today. I got a new cap, rotor, plugs, wires and fuel filter. The miss is now more frequent and more pronounced. It's fine at idle; it only misses under load while driving, not while sitting in the garage. What's the diagnostic procedure? I will verify pump pressure first. What should I check next? Vacuum leaks? I put my scanner on it tonight and found a code 38 (brake switch stuck off) but I doubt that has anything to do with it.

 

Well typically when there is no engine light set off its cause its a fuel related issue. So you are on the right track. Get yourself a pressure tester for 40 bucks and post up your results. You are probably going to be due for a spider and nut kit, depending how much you wanna spend. The whole works can be had for around 200 bucks online. A fuel leak would explain all the crud built up on your plugs too.

You want around 58-60 psi running, key on the pressure should go up and hold, key off it should not drop off fast at all.

Pretty much all of us that have these trucks have had to do this by now. If thats the original injector (all black legs) its done pretty good in its life.

Another option if you dont need to drive the truck for a couple days. Pull off your old injection unit, and take it to a local guy to repair. Here we have a "Fuel injection plus/battery doctor" shop and thats what they do there.

 

I replaced the spider and nut kit on my wife's '93 Jimmy so I'm well familiar with it. I have a spare spider from my wrecked '94 Jimmy that I could swap in if necessary.

In June I replaced the fuel pump in my Blazer. I tested the fuel pressure many, many times because the fuel pump was having an intermittent problem. Every so often when it was warm out the fuel pump wouldn't come on after sitting for a while. To verify the problem was the pump I drove around all day with a fuel pressure gauge on the line and a fused, switchable lead going to the fuel pump prime connector. After I verified the problem I replaced the pump. Once the pump was replaced I tested it again and the pressure was fine, 58-60psi, held for 10 minutes after the key shut off.

Since it's an Airtex pump I'll test the pressure again. I have a Delphi on the shelf waiting for the inevitable failure.

 

My sister had a baby on Christmas Eve so I wasn't too concerned with the Blazer for a couple days.

Yesterday I got back to work on it and discovered that when I installed the new cap, rotor and wires I knocked the vacuum hose off the back of the intake. Duh. I was surprised that the idle didn't go up as a result. One of the screws holding the cap onto the distributor had come loose and the cap wasn't sitting snug on the distributor. Once that was fixed the Blazer returned to its old, powerful self. I did a WOT run over Graham Hill and it flew over the top at 70MPH.

I also checked the fuel pressure and did a leakdown test and the results were satisfactory. The pump delivered 60psi and held at 58 for at least 20 minutes. I also checked the Manifold Tuning Valve and found both sides of the intake to be nice and black.

Now back to working on my '84 Park Avenue...