98 Jimmy - Fuel Delivery Troubleshooting

4.3 liter, 4 door, 4wd.

I replaced my fuel pump and fuel filter a month ago. Everything seemed fine until recently when it started acting up. Wife got stranded one day because it wouldn't start. By the time I got there it had started, so she drove it home. I took it to work the next day and just as I got a block away from work it died on me and would not start. 20 minutes later it started up. On the way home from work it did not want to run right, could not get it to go over 45 mph. It wanted to die, and it did when I was halfway home. Waited 20 minutes and no start still, held the pedal all the way to the floor and got it to start. Nursed it home doing 30 mph with the flashers on going down the highway.

I have checked the plugs, cleaned the throttle body and the IAC valve.

So...I got a Fuel Pressure Tester and here is what I have:

Cold pressure = 55 psi
Engine running = 55 psi
Engine off = 55 psi (after 5 minutes pressure is at 49 psi)

I blocked the return fuel line, turned the key to the on position and the pressure pegged up to 95 psi. Immediately turned the key to off.

Is it Fuel Pressure Regulator time???

Isn't 55 PSI the low end of the recommended pressure? Somewhere in my mind 65 PSI is normal. There is a FPR under the upper manifold. Also you may have an injector leaking. Also under upper intake. What codes are you getting? Has your check engine soon light appeared?

The Check Engine light has never come on. I do not have a code reader, but if the light ever does come on I will take it to a shop and have them read it. The range is supposed to be from 60 to 66 psi. 55 is too low. What bothers me is that when I blocked off the return line the pressure pegged way up there. Maybe I didn't properly block off the line. My fuel lines are metal and semi-rigid vinyl and there is no way to pinch the line to restrict the flow. So I had to separate the quick connector of the return line and fashion a stopper to block off each section. I don't know if this was the correct way to do it but that was all I could think of. Maybe someone knows a better way to block the return line to measure the true output of the fuel pump.

I have been using the diagnostic charts from AllDataDIY, but was looking for a second opinion before I commit to buying the FPR. The interior of the upper intake manifold did look like it needed cleaning, and who knows what I may find in there? You may be right! I may have a leaking injector, or the spider may be leaking, or there could be a wiring problem. I have read so many posts from others with similar problems, but there never seems to be a common solution. So I guess I will have to let you all know what I end up with. Thanks for the reply.

If pressure pegs out with return line blocked off and is low unplugged the fuel pressure regulator is bad.
MT

MT-2500,

Thanks for the info. I am going to do the repair this weekend. I will be sure to post back my results.

You are welcome.
Always check pressure cold and hot after 20-30 minute run.
Good Luck
MT

I purchased and installed the Fuel Pressure Regulator. I cleaned all of the fuel injectors and the inside of the plenum and top of the intake. No luck! Did not fix the problem. When I turned the key to the on position the fuel pressure initially goes to 63 psi, then settles back to 56 psi. It holds this pressure for 5 minutes. I started the engine and the pressure remained at 56 psi, just like before.

I did not have a long enough hose to route the gauge to my windshield, so I decide to see if I could drive it 10 miles to the parts store to get one. Bad idea. I got about 8 miles down the road and it started acting like it was losing power. I had left the gauge installed on the shrader valve, so I pulled over in a parking lot and opened the hood to check the pressure. The needle was bouncing erratically between 50 & 60 psi. Got back in, put it in reverse and it stalled. Opened the hood back up and the pressure had dropped to 48 psi. I pressed the button to relieve the gauge pressure and got a paper and pencil to record the readings over the next 50 minutes (that was how long it would be before the wife could get over to me with a tow strap). The following are psi readings taken with the key switched to on/off, (knew it was useless even trying to crank the engine.)

@ 2 minutes - 22/20, @ 5 min - 28/26, @ 10 min - 30/34
@ 15 min - 36/38, @ 20 min - 38/42, @ 25 min - 40/40
@ 30 min - 40/40, @ 35 min - 40/44, @ 40 min - 42/46
@ 45 min - 42/44, @ 50 min - 42/46.

I tried to start it at this time but it just cranked. Anyway, we towed it home and when I got it back into the garage the pressure was up to 50 psi with key turned on, engine off...but it still wouldn't start. One hour later I went out to the garage again and checked. Its back to 63 psi when the fuel pump runs for 2 seconds, and then settles back to 56 psi. Friggin thing did start and run though.

Why would it do this? It almost seems like a heat problem or something. Weird how the pressure slowly builds back up over time to where it will start again.

Sorry for the long post...but I wanted to put in as much info as I can in hopes that someone can point me in the right direction. I am getting frustrated and could really use some help here please!

Weak fuel pump.
The hotter it gets the lower the pressure gets.
About time for a good AC-Delco/delphi replacement.

I was afraid you would say that. The brand I put in was a Carter from Checker Auto. I thought Carter was a reputable brand. Didn't they use to make carburetors? Oh well, at least it will be easier to replace the fuel pump this second time around. I can get a Delphi from O'Reilly for about $100 more than what I paid for the Carter, but add in the man hours spent on having to do it twice, and the cost is considerably more. Thanks for the help!

Carter used to be good several years back but went to pot.
The Airtex came along and took over the market.
They also used to be good but went to pot.
For about the last year they have had a lot of comebacks and bad pumps out there.
Carquest has dropped them like a hot spud.
They have switched all there pumps to Delphi.
Do some checking around for a good price on the AC-delco/Delphi pumps.
My cost on AC-delphi as fuel pump is about 25 dollars over airtex.
My parts place will adjust a warranty on a airtex pump to a AC pump for about 25 dollars more.
Good Luck