GM Truck Club Forum banner
1 - 5 of 5 Posts

·
Registered
1998 Chevy K2500 Cheyenne 5.7L vortec v8
Joined
·
1 Posts
Discussion Starter · #1 ·
Hi I have a 1998 k2500 Cheyenne with about 305000 miles. It have the 5.7L v8. The issue I am having is that the truck has low oil pressure and idle at a stop. The pressure and idle is fine when you first start the truck but as you go you can the oil pressure drop. It usally drops to around 20 while driving and about 4-7 at stops. this idle usually goes to around 700ish rpms. I've heard that 700 rpm is normal idle but I am not sure. It has recently started doing it in park too.
 

·
Registered
‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
Joined
·
3,811 Posts
Howdy and welcome. Start with checking your fuel pressure. There’s a valve on top of the engine back near the distributor.
 

·
Registered
Joined
·
16,239 Posts
Your idle speed is a little high. In gear at a stop it should be closer to 550. The 700 number would be normal for Park, or Neutral.

You could have a failing oil pressure sensor; I would check the oil pressure to see what it really is.
 

·
Registered
Joined
·
303 Posts
GM trucks are known to have wonky oil pressure sensors/senders during the 90s and early 2000s. I would start with going to harbor freight and buying a engine oil pressure test kit they are cheap and good to have on hand, verify the oil pressure.

You do have 305,000 miles so it has lived a long life so I wouldn't complain if it does actually have low oil pressure however those 350's are known to go much longer especially if maintained.

You could have some worn out cam bearings causing this issue. But start with the simple stuff first and check that oil pressure.

The oil pressure will drop further as the oil heats up.
 

·
Registered
Joined
·
3,992 Posts
do you have a vacume brake booster? is it leaking? when these start leaking it only happens when the brakes are pressed. a slight hiss may be heard in the cab.

I personally believe, all these old boosters are near the end of their life. there have been multiple failures on original boosters over the last couple years.

the thing is, people have idle problems but they dont realize it is because of a brake part. when its really bad you will hear a loud hiss inside the cab when you press the brakes and of you hold it long enough, the truck will almost stall when you try to proceed.

you can test this with an obd2 scanner and while watching the short term or long term fuel trims while holding the brakes if you hold it long enough they will rise all the way to 100%.

Al
 
1 - 5 of 5 Posts
Top