Runnability issue hardest i ever had to diagnose

This engine used to soundlike a jet from air intake when I blipped the throttle.

If you hook a vacuum gauge up to the engine, and bring it up to about 1500 RPM in Neutral/Park, and hold it steady, the vacuum should hold steady at about 20". If it starts to fall off, that points to a clogged exhaust.

I have a vacuum gauge in route finally hope to have it tested in an hour or so.

this is a longshot -- but find a factory manual and double check the plug wire order. They might be mixed up a little at the coil pack?!? I am grabbing at straws here.

Nah they are good vacuum was 14.5 at idle 15 at 1500 rpm

Trystlore wrote:

Nah they are good vacuum was 14.5 at idle 15 at 1500 rpm

Your vac could be higher, I am thinking exhaust is impaired....

Leaning there as well gonna open it up Tuesday and check engine reaction

Its odd that all of the diagnostics nobody has mentioned to check the fuel pressure. That can lead to all the symptoms you mention and can be as simple as a clogged fuel filter. The next thing has already been mentioned and thats a clogged cat but you will actually loose power the warmer the car gets. GM's are prone to that but the symptoms are very pronounced.

rivi95era wrote:

Its odd that all of the diagnostics nobody has mentioned to check the fuel pressure. That can lead to all the symptoms you mention and can be as simple as a clogged fuel filter. The next thing has already been mentioned and thats a clogged cat but you will actually loose power the warmer the car gets. GM's are prone to that but the symptoms are very pronounced.

It's entirely possible, but rare. Changing the fuel filter is certainly a worthwhile idea, but I have seem OEM fuel filters with 200K on them.

My '05 Yukon didn't even have a fuel filter. They relied entirely on the in-tank pickup screen (sock filter). That's got almost 200K on it and still on the original fuel pump.

deekster_caddy wrote:

rivi95era wrote:

Its odd that all of the diagnostics nobody has mentioned to check the fuel pressure. That can lead to all the symptoms you mention and can be as simple as a clogged fuel filter. The next thing has already been mentioned and thats a clogged cat but you will actually loose power the warmer the car gets. GM's are prone to that but the symptoms are very pronounced.

It's entirely possible, but rare. Changing the fuel filter is certainly a worthwhile idea, but I have seem OEM fuel filters with 200K on them.

My '05 Yukon didn't even have a fuel filter. They relied entirely on the in-tank pickup screen (sock filter). That's got almost 200K on it and still on the original fuel pump.

The lifetime of a fuel filter is entirely based on where you are and where the fuel is refined. Some refineries are dirtier than others hence the reason for a fuel filter but they are all in a sense dirty, lol  Having worked at a fuel station for quite some time a lil while back I got to know the transporters very well and they showed me how to get samples out of the in ground tanks. Nasty stuff before it goes through the pump and the fuel stations that have the screw on style filters at the top of the pump hose, REALLY Dirty!! Something else a lot of people don't know is most of the fuel stations that have three grades just mix 93 and 87 together to achieve 89. (US Octane and method)

Changed fuel filter last week I will throw a fuel pressure tester on it tomorrow before I cracked it open. New fuel filter helped somewhat. But not as much as expected

Trystlore wrote:

Nah they are good vacuum was 14.5 at idle 15 at 1500 rpm

Nope, that isn't normal. I have a vacuum/boost gauge installed on my 153,000 mile 98 Riv. It pulls 20" at idle all day every day. You either have a vacuum leak somewhere or a clogged exhaust.

Went all around the vacuum lines and intake with starting fluid since hose inspection was turning up any leaks.No leaks that we could find. Don't have a smoke machine anymore so gonna temporarily figure no vacuum leak. Weather permitting going to Unbolt the exhaust tomorrow and see if that solves my obvious issues. Though considering an issue I had when I was changing my plugs and a few other things my thoughts heavily lean towards the partially clogged exhaust.

These are my readings, fully warm in Park, at normal idle.

[quote="LARRY70GS"]These are my readings, fully warm in Park, at normal idle.

oh man thats fancy!!!   

I know right =)