Need help interpreting fuel pressure test

[mudpie]

I had pulled the #1 plug and propped it up next to the brake booster so I could reach in the window and crank the truck and still see the plug. The spark was mostly orange, but a little blue between the electrodes on the plug. Seemed fairly strong, but I'm not a Chevy guy. My Volvo has run with less of a spark, so I assume it's ok, but assumptions are rarely good. Like when I assumed yesterday that my TPS was the problem.

I'm guessing there's a sensor or module of some sort that's causing my problems now. I just have to track it down. The crank sensor gave me some issues about 8k miles ago and it was replaced. Nice thing with that though was that it had a drivability issue, and gave me a code for the crank sensor. Swapped it, and the problem was solved.

My experience with other non-Chevy's has generally been that an ignition module will suddenly die, and the vehicle stops, while other electrical stuff generally goes bad over time and gives you a warning, even if it's a very short period of time. That's why my thought now is the module, but as I've mentioned, I know very little about the quirks of a Chevy.

Autozone has a Wells tester that can test the ignition module, so I'm going to check that out. That leads me to a question though....

I replaced the distributor about 2 years ago, and I recall there being a module in the distributor. What's that one, versus the one mounted next to the coil?

Thanks for posting the troubleshooting info. I'll go through it when I've got more time than a lunch break.

EDIT: I think I answered my own question. The module in the distributor is just the Hall sensor, right?

 

[TruckinAin4Sissies]

Here's a video of when I did mine

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[mudpie]

Long story short. Well, long story not so long....

I found the problem. It was the rotor and cap. Pulled them off to check TDC on #1 and they were corroded inside pretty bad. They were new about 2 years ago when I put the distributor in, so I went on the assumption that there's no way the problem could be that simple. Moral of the story, obviously....don't overlook the little stuff. There was a bunch of moisture inside the cap too, which probably contributed to the problem. Replaced them both under a lifetime warranty and it fired right up.

That was on Friday, two weeks ago. The next day I drove to California for a funeral. I did 1500 miles in 3 days with no issues. Got home, turned the truck off, unloaded my stuff, came back out to run to Safeway and the truck won't start. Pulled #1 plug, set the wire across the master cylinder with the plug close to the booster, cranked it to check for spark and the truck fires right up on 7 cylinders. Put the plug in and it ran find. That was 8 days ago.

Today I'm at Walmart, come out to the truck and it cranks and cranks. Pulled the #1 plug again, checked for spark, and it fired up. Put it back together, get on the highway headed home, get about a mile, and it dies. Just made it to an off-ramp, coasted into a parking lot, and that's where it sits. Tried the plug trick again but it's not working any more. It's fired a couple times but dies pretty soon after.

When I got the new cap / rotor, the manager at Autozone asked me if it was a Chevy. I said it was, and asked why. He told me "they have problems with moisture in the cap". My cap was wet inside. I pulled the new cap off a little bit ago and checked for moisture and there was none. It looks inside like it's firing clean, and the #1 plug I pulled looked nice and light brown like it should.

I tried listening for the fuel pump with the key on, and with a jumper wire in place of the relay, and I couldn't hear the pump running. I can't be sure because it was 5:30 and there was too much noise from rush hour traffic. I'm going now to get a gauge to check fuel pressure.

So, new questions....

Is this moisture in the cap thing actually a thing? This guy at Autozone was telling me they have a customer who drilled a tiny hole in his cap and ran a little vacuum line from the manifold to suck moisture out of the cap. Sounds kinda sketchy to me.

If it turns out to be my pump, this would be a Delphi pump that lasted 2 weeks. I've learned that these trucks eat up fuel pumps, but this seems a bit ridiculous. Why do they die so often? It's got new wiring and a new in-tank filter on it, and I almost never run it low to the point that the pump would run dry.

Any thoughts appreciated.

 

[mudpie]

Well, it looks like I've got fuel pressure issues again. Or still, I don't know

I put a gauge on it and jumped the fuel pump relay. I got 10 psi, and it went up to 15 psi. I only had the jumper in for a couple seconds since I was doing it in a 7-11 parking lot with a paper clip. Wouldn't have been the best idea to leave that plugged in probably.

Just to make sure I had a gauge that worked, I hooked it up to the Ford Ranger I had borrowed to get me there. It showed 60 psi. Gauge is good. I put the gauge back on my truck, turned the key, and it went up to 15. Cranked it and got nothing more for a second or two, then it slowly went up to 50 and started. When I revved the engine, the pressure went up to about 60 just like in the video above, but the idle pressure was exactly 50. Two weeks ago when I put the pump in the idle pressure was 53.

I had an old Alfa Romeo once that would die after a couple hours, then start after it sat overnight. I put a fuel filter in it and it ran great. All I could figure is that there was sediment in there that would settle overnight, and after a couple hours of running got stirred up enough to clog up the flow. That's about the only thing I can think of now. Fuel pump is new, in tank filter is new, FPR is new. What else is there? I know I overlooked the obvious with my rotor and cap, but the fuel filter has maybe 10k miles on it and the inside of the tank is clean. I find it hard to believe it's the filter. Especially since I drove the truck 1500 miles to California and back a week ago with no problems.

So is this pump maybe overheating somehow and the pressure drops below 50 and the truck dies? I'm grasping at straws....

 

[shamrock246]

Have you checked the condition of the gray wire and voltage drop back by the pump that is the power wire coming from the relay up front.When it's running pull the relay out of the socket and it should remain running (power being fed by the oil pressure switch) How is the ground connection on the frame rail by the pump i ran a ground wire from there up to the battery.

 

[mudpie]

I haven't checked the voltage drop. I'll try to do that today, and pull the relay. The ground on the frame should be solid. I spent a considerable amount of time with a wire brush on a drill cleaning up the frame, the bolt, and the connector on the cable when I put the pump in two weeks ago.

 

[mudpie]

Went by on the way to work and tried to check the relay. It wouldn't start at all. It started last night after I cranked it for a while, when I was checking the fuel pressure. Wouldn't go today. I would barely fire, and sputter like it's running on a couple cylinders, for about 2 seconds, then die. I'm assuming fuel pressure has dropped to just slightly under 50, since it was at 50 last night, and I've been told 50 is the absolute minimum it needs to run.

Gotta get it home and jack the bed up again. Good thing I only put 4 bolts back in in last time.

 

[mudpie]

I jumped the relay and it starts. Pulled the jumper wire and it ran for about another second and died. Put the relay in and it won't start.

I have another relay that's been in the glove box since I bought the truck. Put that in and it starts, so at a minimum I've got a bad relay I guess. Pulled the second relay and it dies again in about a second.

I haven't checked fuel pressure yet with the 2nd relay. I'm doing this in the rain at the moment. If it's supposed to stay running when I pull the relay, but it doesn't, what should I be learning from that?

 

[mudpie]

I guess it was the relay. Drove it home 4 miles with no trouble. I pulled over a couple times and shut it off just to see if it would restart and it did, instantly. At one point I stomped on it going up a hill and it didn't hesitate at all. Hopefully this ends my troubles.

A few remaining questions, if anybody has any thoughts...

If I pull the relay, it dies. It was indicated above that it should continue to run. Should it? If so, any thoughts on what I should be checking?

I put the gauge on it before I drove it home and it read zero psi running. I put the gauge back on the same Ranger as yesterday and it read 60 psi. Are these trucks known for having any issues with the schrader valve in the fuel line? I looked at the pin in the valve and it doesn't appear bent, but something is going on. Most of my problems seem to have originated from not getting accurate readings from what I thought was a faulty gauge, but now I'm thinking maybe wasn't. The valve has had the cap on it for at least the 3 years I've owned it, and doesn't appear dirty or damaged.

I appreciate all the input and suggestions. If any of you ever find yourself in Olympia, WA, I'm more than happy to buy pizza and beer.

 

[east302]

The VCM energizes the relay coil to get voltage to the pump. If you pull the relay, to me that kills the voltage to the pump but I’ll defer to others on that.

With engine off, press the Schrader valve to see if you get fuel out of it. Other than that, I’m not sure how you would test for proper function.


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