5.3 hesitation, stumble, lean and random misfire codes, worse when cold.

[kleake]

Originally Posted by mogyver69

Hey guys, the problem this guy is having is a vacumn leak from his upper intake manifold gasket.

I have since sold this suburban this past summer, but the problem wasn't as bad as it had been. It wasn't solved as it still had a rough idle, but it had definitely improved from where it had been. I did change the lower intake manifold gasket and it didn't seem to make any change at the time, but I'm not sure what the upper intake gasket is as this is a 1 piece intake. I do see a lot of people that say the gasket solved the problem, but I'm thinking mine either had a crack or some other leak that I never found. I did search all over the place, even spraying carb cleaner and such and never found the source.

[jyount]

Originally Posted by mogyver69

Hey guys, the problem this guy is having is a vacumn leak from his upper intake manifold gasket. Theres a bulliton for this issue but its probly out of warranty... still the bulliton helps the dealer mechanics with what to look for....Nothing bothers me more then someone telling this poor guy to go to the dealer and spend a few bucks.. I have been a dealer mechanic for yrs. 1 out of 10 mechanics actually knows what there doing.. Half the time the other mechanics were in my stall asking me to help them rather then opening a book and reading the scan tools... I commend people for trying to learn on there own.. I own a 99 silverado with the 5.3L with the same issue and I am getting ready to take a look at mine for the same issue. Also check your pcv system the plastic vacumn lines break and leak often. Hopes this helps!

Would have to agree with this guy, true mechanics are few and far between. Fixers are not the same as parts changers. The older LS series engines had intake manifold gasket breakdown from fuel causing this. I believe the old gaskets were orange and the newer ones are green. GM figured it out about the time "flex fuel" was popular. Only problem was the ethanol content was what was eating it and all fuel made now days has ethanol in it. The manifold is not hard to replace gaskets on. I used to be a dealer tech too, if I remember right that is one of the jobs you did ok on since we were paid flat rate. IE it took considerably less time than was billed for the job...

[j cAT]

Originally Posted by jyount

Would have to agree with this guy, true mechanics are few and far between. Fixers are not the same as parts changers. The older LS series engines had intake manifold gasket breakdown from fuel causing this. I believe the old gaskets were orange and the newer ones are green. GM figured it out about the time "flex fuel" was popular. Only problem was the ethanol content was what was eating it and all fuel made now days has ethanol in it. The manifold is not hard to replace gaskets on. I used to be a dealer tech too, if I remember right that is one of the jobs you did ok on since we were paid flat rate. IE it took considerably less time than was billed for the job...

this guy has used airtex replacements so why would you expect the pressure of fuel to be correct. his first post he thought 43 psi was normal pressure ..

YOU USE AIRTEX YOU LOOSE !

[jyount]

Not saying it is ever, and I reread my post, not there. What I will say is that for every pump we replaced in this vintage, we probably replaced 15 intake gasket sets. Multiple problems for the OP? Maybe so, but we will not know because he got rid of it. True both can cause this issue, but hard starts, powering out at higher loads, and stalls are far more common to fuel pressure issues than lean codes are.

[kleake]

Originally Posted by j cAT

this guy has used airtex replacements so why would you expect the pressure of fuel to be correct. his first post he thought 43 psi was normal pressure ..

YOU USE AIRTEX YOU LOOSE !

I am not saying airtex is the best thing out there, but the cost of most other OEM versions of this pump are simply ridiculous! The point is, the fuel pressure running never changed (or at least very little) from the original noisy pump, to the replacment, to the second replacement. I NEVER had any issues when the rpm was above about 1500 or so, and WOT always worked without any cutting out. Wide open performance was fine, which would tell me the fuel pressure was acceptable. Even at idle when I unplug the regulator, pressure would go up to 60 and guess what, the problem still existed with very little change. The lower intake gasket was changed to the newer style and that didn't seem to make any noticable difference at all and I could never find any cracks or leaks of any kind. Just because I couldn't locate any, doesn't mean there isn't any, but I looked pretty hard and used carb cleaner to help search. From everything I can determine, and what I see from others indicates there was a vacuum leak somewhere though. I also read about a re-calibration of the computer on some models, I never had this done, but it very well could have corrected the issue as well. The way I look at it though, if a problem is getting worse, it's not the computer, it's a component failing and a calibration of the computer is simply a patch.

Either way, I can agree that Airtex isn't the best pump out there, but in this case, I am pretty positive that it is not the issue.

[j cAT]

Originally Posted by kleake

I am not saying airtex is the best thing out there, but the cost of most other OEM versions of this pump are simply ridiculous! The point is, the fuel pressure running never changed (or at least very little) from the original noisy pump, to the replacment, to the second replacement. I NEVER had any issues when the rpm was above about 1500 or so, and WOT always worked without any cutting out. Wide open performance was fine, which would tell me the fuel pressure was acceptable. Even at idle when I unplug the regulator, pressure would go up to 60 and guess what, the problem still existed with very little change. The lower intake gasket was changed to the newer style and that didn't seem to make any noticable difference at all and I could never find any cracks or leaks of any kind. Just because I couldn't locate any, doesn't mean there isn't any, but I looked pretty hard and used carb cleaner to help search. From everything I can determine, and what I see from others indicates there was a vacuum leak somewhere though. I also read about a re-calibration of the computer on some models, I never had this done, but it very well could have corrected the issue as well. The way I look at it though, if a problem is getting worse, it's not the computer, it's a component failing and a calibration of the computer is simply a patch.

Either way, I can agree that Airtex isn't the best pump out there, but in this case, I am pretty positive that it is not the issue.

with a 5.3L engine you need 60-62 psi key on engine off. when the engine runs it must be above 52psi. normal psi is 57 psi engine running.

with a vacuum leak the engine will hi idle. rpm at idle should be 650 rpm.

PCV and vacuum lines are replaced with any cracking which will cause hi idle.

a low rpm idle is from the IAC / throttle body dirty . stumble and random misses would be low fuel and or a restricted exhaust.

since you dumped it that is a sure fire way to solve a vehicles problem.

[kleake]

Originally Posted by j cAT

with a 5.3L engine you need 60-62 psi key on engine off. when the engine runs it must be above 52psi. normal psi is 57 psi engine running.

with a vacuum leak the engine will hi idle. rpm at idle should be 650 rpm.

PCV and vacuum lines are replaced with any cracking which will cause hi idle.

a low rpm idle is from the IAC / throttle body dirty . stumble and random misses would be low fuel and or a restricted exhaust.

since you dumped it that is a sure fire way to solve a vehicles problem.

Idle was always 650 and was never above or below by more than 100. Throttle body was cleaned, although I had not dipped it. Exhaust didn't seem to be an issue because high rpm power and performance was excellent. The only issue was rough idle and low rpm /heavy load miss, which I agree would indicate fuel. I don't think it was pressure though, but possibly dirty/fouled/worn injectors.

And I didn't dump the vehicle to solve the problem, I don't do that. I am upgrading to a 5th wheel trailer and a suburban just doesn't tow that very well. I had the Suburban for 9 years and we liked everything about it, except for this issue which we would have dumped it looong before now if that had been a show stopper. I upgraded to an 08 F250 diesel. We was tempted to keep the Suburban as a 3rd vehicle, but opted to sell it anyway as it would get very minimal usage and we have enough vehicles to drive already.

[j cAT]

Originally Posted by kleake

Idle was always 650 and was never above or below by more than 100. Throttle body was cleaned, although I had not dipped it. Exhaust didn't seem to be an issue because high rpm power and performance was excellent. The only issue was rough idle and low rpm /heavy load miss, which I agree would indicate fuel. I don't think it was pressure though, but possibly dirty/fouled/worn injectors.

And I didn't dump the vehicle to solve the problem, I don't do that. I am upgrading to a 5th wheel trailer and a suburban just doesn't tow that very well. I had the Suburban for 9 years and we liked everything about it, except for this issue which we would have dumped it looong before now if that had been a show stopper. I upgraded to an 08 F250 diesel. We was tempted to keep the Suburban as a 3rd vehicle, but opted to sell it anyway as it would get very minimal usage and we have enough vehicles to drive already.

what do you think about the 08 ford ? how does it compare with the GM new new style trucks 2007-2014

[kleake]

Originally Posted by j cAT

what do you think about the 08 ford ? how does it compare with the GM new new style trucks 2007-2014

I didn't get a chance to drive one of the newer GM trucks before I bought this one since I couldn't find any on any lots. All that I did see were gas and not diesel. My brother in law has had 2 Dodge diesels and loved the power, but they rode rough and he had many issues with death wobble. He bought a low mileage 08 Ford and loved it and after I rode in it I agreed that it fit what I wanted. I did a lot of searching and found this one loaded with tuner, full delete and dressed just like I like. I can say I have no issues, even with 180k already on it. The thing has ungodly power! There is a hill near our house that is really steep, the suburban pulling our camper up would be in first gear, foot to the floor and would just hold about 25-30mph. This thing will be in 3rd gear gaining speed without any problem at all. There really is no comparison of power whatsoever. It pulls very smooth and I can't even tell my small boat is even hooked to it. The bigger boat gives it a decent load, but still pulls great. I do hear the GM trucks get better mileage, and may have more creature comforts, but I also hear they don't have the power nor the reliability, but I can't confirm that. I do know that I am 100% happy with my purchase so far.

[j cAT]

Originally Posted by kleake

I didn't get a chance to drive one of the newer GM trucks before I bought this one since I couldn't find any on any lots. All that I did see were gas and not diesel. My brother in law has had 2 Dodge diesels and loved the power, but they rode rough and he had many issues with death wobble. He bought a low mileage 08 Ford and loved it and after I rode in it I agreed that it fit what I wanted. I did a lot of searching and found this one loaded with tuner, full delete and dressed just like I like. I can say I have no issues, even with 180k already on it. The thing has ungodly power! There is a hill near our house that is really steep, the suburban pulling our camper up would be in first gear, foot to the floor and would just hold about 25-30mph. This thing will be in 3rd gear gaining speed without any problem at all. There really is no comparison of power whatsoever. It pulls very smooth and I can't even tell my small boat is even hooked to it. The bigger boat gives it a decent load, but still pulls great. I do hear the GM trucks get better mileage, and may have more creature comforts, but I also hear they don't have the power nor the reliability, but I can't confirm that. I do know that I am 100% happy with my purchase so far.

the ford does have the power and most all install the tuners with these ..since most use these diesels to tow campers etc..

the gm trucks do appear to have a nicer interior but the reliability on the 2007-?? is not very good.

[kleake]

Originally Posted by j cAT

the ford does have the power and most all install the tuners with these ..since most use these diesels to tow campers etc..

the gm trucks do appear to have a nicer interior but the reliability on the 2007-?? is not very good.

I have heard the same, but overall I had much less feedback on the GM since there aren't nearly as many on the road. It's funny, I typically will see only 1 or 2 GM diesels (3/4 ton variety) in a given week. I will see 5 or so per day of ford or dodge. That in itself told me how the reliability must be. And yes, the difference in power from my brother in laws low mileage in stock condition to my high mileage tuned truck is so much different, it doesn't even feel like they are the same truck. I have seen dyno reports of trucks with nothing more than exhaust, cold air intake and a tuner putting out 600hp and 1000ft/lbs of torque.