I've been driving my new 94 Blazer (vin W) around for almost a week and loving the heck out of it. Last week I drove down to Puyallup to visit my grandfather and when I left it wouldn't start. It would turn over but wouldn't fire. After cranking it several times I decided to call AAA and have them bring it home for me. I got it home and it started right up. Puzzled, I decided to replace the coolant temperature sensor and the sender for the gauge. Replacing the sender gave me a functional gauge on the dash.

Today I drove the Blazer again and it refused to start twice. The first time I waited about ten minutes and it fired right up. The second time I waited an hour and it started. I was able to get it home.

I parked it right in front of the garage, changed my shirt and went to work diagnosing the problem. I put the fuel pressure gauge on the fitting and turned on the key. First time it only went up to 20psi. Second time it went to 40. Third time it pegged at 60 and held there for five minutes after I turned off the key. That suggested to me that the fuel pump is bad.

I wanted to verify the pump's operation so I disconnected the wiring harness from the relay. I used some old wire terminals and a jumper wire to jump the hot lead coming in over to the power wire going to the pump. The pump immediately came on and pegged at 60psi. My first thought was that it was a fluke. I tested it at least twenty more times and every time the pump came on at full strength at 60psi.

That made me question the relay. I took it off and tested it with a nine volt battery. Every time I touched the test wires to the battery the relay clicked. I hooked up my multimeter to the other terminals and every time the relay closed there was continuity with 1Ω resistance. The relay appeared to check out.

Next I tested the wiring going to the relay. The ground checked out. I tested the voltage on the control wire going to the relay. I had my daughter turn the key on while I read the multimeter. I got 12.3V from the control wire for about two seconds each time she turned the key on.

Based on my testing of individual components the fuel pump appears to be OK when it gets 12V directly. The relay appears to be OK. The voltage and ground to the relay appears to be OK. If all of those things are functioning properly individually they should work OK collectively, right? The only variable I can think of is whether the fuel pump or relay got overheated and malfunctioned. When I first got home I only took about fifteen minutes from the time I hit the driveway until I had the fuel pressure gauge on it. By the time I was finished testing it was two hours later and quite a bit cooler outside.

Could the oil pressure switch be faulty? I haven't suspected any kind of leaking injector/line problem because the previous owner replaced the spider just prior to me buying it. Also, since the system didn't pump up to full pressure on some of the tests that leads me to question the fuel delivery system more than the injectors.

Give me your suggestions. I'm open.

 

Could be a weak ground to the pump. Sometimes grounds will check out fine when you check the continuity of the wire, only to fail when attached to a load. Had this happen to the rear wiper motor of my buddies 03 Tahoe... left me scratching my head for a week.

 

That's exactly the kind of suggestion I was looking for. I hadn't considered a bad pump ground. Do you know offhand where the pump ground is located? I'm hoping I won't have to drop the tank to fix this thing.

 

I'm not really sure as I've yet to mess with the fuel pump on an s series truck, but you might be able to get away running a test ground to the pump with gator clips hooked up from the pumps connector to a good ground source nearby. Be careful not to make any arky sparky!

 

Update: I spoke to an electrical engineer friend of mine today. He suggested that the relay may degrade under load causing the kind of intermittent fuel pump problem I've been having. I swapped the relay with a good one from my wrecked 94 Jimmy. So far the Blazer has been starting and working flawlessly. I'll have to drive it out on the freeway and get it really warm and see how it does under those conditions. I'm hoping it's just the relay. That would make me very happy.

 

Here's the latest on my Blazer:

I drove it up to Bellevue again today. When I restarted it after I had been parked for a few minutes it didn't want to start on the first crank. I cranked it over a second time and it started. I drove it back home and tested the fuel pressure. The first time I turned the key on the fuel pressure went right up to 60psi. When the pump shut off the pressure dropped down to nothing immediately. The second time I turned the key on the pressure went right up and stayed there after I turned the key off. I continued testing the fuel pump by turning the key on and letting it pump up and then shutting the key off after the pump quit running. Sometimes the line would hold pressure after the pump quit running, sometimes it would not. When it held pressure it would hold it for at least twenty minutes. When it did not hold pressure it dropped immediately.

So far the Blazer hasn't stranded me anywhere which makes me happy. My grandmother is having surgery tomorrow so I really don't want to get stranded in the rain somewhere. I'll have to drive it more and see if its behavior changes. In the meantime, what might cause the intermittent loss of pressure? It seems to me if the FPR is bad that it wouldn't hold pressure perfectly some times and lose it completely other times. Is there a check valve somewhere in the pump assembly that might be failing? Give me your ideas.

 

Your possibilities are the check valve in the pump, the FPR, or the 'nut kit'. I agree that the FPR & 'nut kit' should be consistent leaks, but stranger things have happened before. I would adapt your pressure tester to the line coming out of the pump and into the filter under the truck to isolate the pump from the rest of the system and see where that gets you.

 

For now I'm going to drive it and see if it has the serious problem it had before. If I can replicate the non-starting condition then I'll drop the tank and/or fuel filter and get some fitting adapters and test the pressure back there. I also ordered a Light Duty Fuel & Emissions manual from eBay today which should give me a little more info on the fuel/emissions system on my Blazer.

I appreciate everyone's collected wisdom. You've all been incredibly helpful.

 

My '91 S-10 Tahoe had sat for several years and wouldn't start. When I pulled the fuel pump the rubber hose from the pump to the metal outlet tube had turned to putty. New hose...started right up. Seems old S-10's don't like the "modern" gas in California.

Bob
San Diego
San Diego

 

it should be on top of the end frame rail running paralel to the rear bumper. just a eye and bolt clean the frame well when you unbolt it, and scuff it down either with a file thats what I used or wad of 80 grit paper mine was badly corroded when I blasted my frame for painting , although mine was a 93 blazer should be identical