that hesitation may be something as simple as a fuel filter, check it and replace if it looks nesessary, there only 10 bucks. solved my uncles hesitation and he was complaining of the same thing, right at the touch of the throttle. If its really bad it may be straining that pump thats whining.

 

Sorry for the delay in replying but I have been busy. Good news is I think I found the source of part if not all of my trucks problems.

I was looking under the hood still trying to figure out what was causing that rattling sound and I happened to notice my smog pump/air pump sounded funny when I reved the engine. Problem turned out to be one of the notorious plastic vacum lines was broke. So I replaced it with rubber Vac line.

Then I check my EGR valve and noticed when you put vacum on it , it will open but then leak back shut. Pleas correct me if I am wrong, but isn't supposed to stay in the open position when vacum is applied? I think it has a hole in the diaphram so I am going to compare my finding to a new EGR valve today at the parts house.

The rattling noise I am almost certain is my PCV valve. I noticed the rattling changed with the throttle postion not the engine rpms. So I was pretty sure it was a vacum based problem. I also notice my PCV vacum line was cracked which could explain my hesitation and some times high idle. This may also explain my ALWAYS LEAN trouble code.

So later today I am going to pick up some vacum hose and a PCV valve along with a Fuel filter. I will try to post my results a little quicker this time.

 

It wasn't the PCV valve.

I think it may be the air pipe from the pump. I will just keep checking.

I am going to install the new fuel filter today. I also put a tach in yesterday so I can monitor RPMs. It likes to Idle between 800 to 1000 and sometimes it seems to idle a little rough. Does anyone know if the 4.9 is evenly spaced or oddly spaced firing pattern ( degrees between firing)?

I also forgot about checking a new egr valve for leak down.

Thanks for your help.

 

It is not the fuel filter, changed it and it runs about the same. the filter did have some black sediment in it bu it wasn't full of trash. I still need to check the fuel rail pressure though.

What is the fuel pressure supposed to be?

I am wondering if the Idle Air Control valve is causing my high idle? Reason: I can unplug it when the truck is cold or hot and it doesn't really make a difference. But could that also be a sign of a vacuum leak and the valve is staying closed?

Where can I find a vacuum diaghram?

Sean, I know you have a link.

What is the Vacuum gauge supposed to read when the truck is idling?

The idle when cold is about 1500 then it falls to about 1000-1200 after a few minutes but it never idles low like my other vehicles (750-800). that could be the sign of a vacuum leak, right?

What is the Idle speed for a 4.9L with the manual tranny when the engine is at operating temp?

Can I do away with air pipe ( could be the rattle ) going to the exhaust since it is behind the O2 sensor?

Can I do away with the Airpump and plumbing and replace it with a idler pulley?

or if all else fails.....

I could just turn the radio up really loud no more rattle.

 

The rapid blinks at the beginning of the test is the identification of the PCM. 2 blinks=4 cyl. 3 blinks=6cyl. 4 blinks=8cyl. Agreed, it was really stupid. For the rest, stick with Sean.

 

To clear one thing up, apparently you didn't get a code 33. It must have been code 111- system pass. I don't have any vacuum diagrams. The EGR should hold when vacuum is applied and held. You can get rid of any air pipes as long as you don't have emissions inspections, but you have to leave the control solenoids in place and hooked up. You don't even need an idler pulley to put in place of the pump, just a smaller belt. IAC is a good place to start with a bad idle.

 

There should be a vacuum diagram on the underside of your hood. When your truck is idling, it should be pulling about 23 hg of vacuum.

 

Rattle may be muffler or tailpipe hanger or a cat comming apart. Crawl under (after chocking vehicle) with running and see where sound is from. Might be as simple as a heat shield on cat or exhaust manifold. HTH Timok1

 

Okay I know my EGR valve is not holding because I put a vacuum on it and it would leak down slowly. So I know it is Bad, but could it cause hesitation?As for the deleting air system, are you talking about the vacuum control solenoids like the one for the EGR . I have 3 or 4 on the side of my intake. So I leave those and the EGR valve, but I can scratch the pump and air pipe? I do have a vacuum diagram uder my hood.

I tried cleaning the IAC before but I do not know if it is working properly, I may clean it again.

Also have a new discovery on the vacuum leak and idle. I put a gauge on it and it held about 22 in (my gauge may need calibrating) when I reved it up the vacuum went down to around 15 and when I shut the throttle it went back up to over 25. The vacuum was steady not fluttering. I think it may not be a bad leak if it is one at all. I do know that my vacuum canister will leak if you move the lines. I am going to fix that. But when
I was messing with the throttle and I pushed the it closed really hard and the truck idled down. So I am thinking now maybe my problem is carbon build up in the throttle assembly. I may take it off and clean it.

Guys thank for all the help. I shall report back soon.

 

While you have the throttle body off, you might want to replace the TPS as well, if you have the scratch. I did that and cleaned my throttle body and it smoothed out some of the idle and acceleration.