Drivability Problem

jeffd · Post by **jeffd** » Tue Dec 19, 2006 11:34 am

I have a 99 4 door 4wd blazer. It is having a problem driving over 40 mph. The engine won't rev up and lacks power. If you try to accelerate it wants to cut out a little. I have had the valvebody in the trans rebuilt recently. I also put a new fuel filter in. The fuel pump was replaced 18 months ago. The fuel pressure is 58 psi with the key on and engine off. It is 51 psi at idle. The trans place said it was either the fuel pump, filter or the cat was clogged. I gutted the cat last night and it made no improvement. There is around 107,000 miles on the truck. I have replaced the cap, rotor, plugs and wires about 20,000 miles ago. It idles good and the service engine light has not come on. It seems to me like it isn't getting enough fuel. Is there anything else to check?

Post by **Walt** » Tue Dec 19, 2006 12:54 pm

A friend had a similar problem several years ago, with a 1996 Silverado. He could hit the gas and accelerate hard, but if he completelly floored it, the engine would bog down. It turned out to be the fuel pump, and he'd just had it replaced.

Post by **HenryJ** » Tue Dec 19, 2006 3:19 pm

Might be a fuel pressure regulator problem? How is the fuel pressure when running and dumping the fuel at the bypass?

There is a pretty good thread about all the tests that need to be done here somewhere.

EGR valve condition is another thing to check, as is the ignition coil and ignition module.

jeffd · Post by **jeffd** » Tue Dec 19, 2006 6:32 pm

Is the fuel pressure regulator built in the rail? The crappy Haynes manual doesn't say much about this.

Post by **HenryJ** » Tue Dec 19, 2006 6:56 pm

The fuel pressure regulator is under the upper manifold assembly.
Removal of the upper intake manifold is necessary for access.

They are a commonly replaced item on the V-8. They use the same regulator, but it is external on those engines.

jeffd · Post by **jeffd** » Fri Jan 19, 2007 6:19 am

It was the fuel pump. It an intermittent problem. Everytime I checked the pressure in the driveway, it was in spec. I finally drove the blazer for 30 miles with the gauge sticking out the hood. When it started to act up, the fuel pressure was around 40-45 psi. The only good part about replacing the fuel pump for the second time it that the parts store warrantied it for me.

Grunto · Post by **Grunto** » Sun Jan 21, 2007 4:57 pm

Check your catalytic converter. I could not rev my truck past 3500 at all with a clogged cat.

An easy way to look for a clog in your exhaust is to find someone that has one of those laser reading thermometer things and just go along the exhaust system with it, if the temp is high then drops after a certain point, its clogged.

HCO4x4 · Post by **HCO4x4** » Sat Apr 12, 2008 2:47 pm

i have been having the exact same problem! it is the fuel pump but every month it does this. im on my fourth pump since christmas and its getting old. the guy at the parts store said it could be the regulator but i replaced it and it actually ran a whole lot worse so i took it out. anyone? i also have the cat cut out because i thought that could be it last time.

Post by **HenryJ** » Sat Apr 12, 2008 4:30 pm

Buy genuine AC Delco fuel pump modules. There is a difference.

HCO4x4 · Post by **HCO4x4** » Sat Apr 12, 2008 4:32 pm

thats what i hear. but if all autozone pumps go out in 1 month how can they sell them?

Post by **HenryJ** » Sat Apr 12, 2008 4:36 pm

I don't have an answer. Maybe they figure you will get tired of changing the cheap Chinese pumps and sell the truck?
They can probably buy half a dozen for the price you bought it for.

HCO4x4 · Post by **HCO4x4** » Sat Apr 12, 2008 4:46 pm

yea. ok well i guess ill have to return it and grab a delco. thanks

HCO4x4 · Post by **HCO4x4** » Tue Apr 15, 2008 7:49 am

i got another autozone pump the other day because they couldnt do refunds without a manager and i need my truck. it runs now but this time it isnt getting as much fuel as it should. my 5th pump and this is the first time its done this new. what is the chance it could be the regulator?

Post by **HenryJ** » Tue Apr 15, 2008 8:59 am

Possible.
Testing fuel system
Follow the diagnostic to determine the part needed.

border man · Post by **border man** » Tue Apr 15, 2008 9:46 am

My truck finally stranded me this past weekend, and I ended up buying an Autozone pump. During the replacement process, I kinked the main fuel line. It is hard plastic, so the kink remains. I believe it is restricting my fuel pressure. Truck runs fine, but when I gas it, it seems to hesitate some. Went to stealership yesterday and ordered a new line ($106)