bwforum

Almost every time I start my 99 5.3L Silverado, whether it has sat all night, or for 15 minutes, it stumbles or hesitates on acceleration for the first 30-60 seconds. I usually jump in, hit the key and throw it in gear and go. I can actually put the pedal 3/4th of the way down and it just won't pull, and sometimes hear a backfire or popping under the hood. The check engine light has never come on since I have owned it. After the initial stumbling, it comes right out of it and runs perfectly, with a very slight hesitation. It currently has almost 99,000 miles on it and I bought it with 50,000 miles almost 4 years ago. I have replaced the fuel filter, plugs and air filter recently and the fuel pressure regulator about a year ago after experiencing the hard starting problems. Any help or suggestions would be appreciated.



UPDATE ON 5/26/2005---IT'S FIXED!!!

After dealing with this for quite some time, I finally solved the problem. It was the Mass Airflow Sensor. I finally unhooked the connection, and the hesistation problem after startup seemed to go away, so I decided I would drop the $200 on a new MAF. It solved my problem, and my truck once again runs great.

Thanks to everyone for their suggestions.

drumminjer

throttle body may need cleaning

Faze3

Definitely clean the throttle body if you've not done it yet.

bwforum

I clean that about every 6 months, when the throttle body gets a little sticky. I bought some spray from GM, and spray it in when it is running, and also give it a good dousing and wipe the butterfly area with a rag. Is there more to cleaning it than that? Thanks for the suggestions so far.

Faze3

See my post here:

http://www.automotiveforums.com/vbul...=throttle+body

bwforum

Faze3,

I tried your recommendations on the throttle body cleaning this weekend, and although the throttle body has never been smoother, it still runs the same. I paid a little more attention to how it runs this weekend as well. After starting, for the first little bit, it just chugs and pops a little. Then just like you throw a switch, it comes out of it, and it runs great. Almost like there something that is sticking, that all of a sudden lets loose, and then it is fine. I have seen some posts of people cleaning the EGR valve and the MAP senson, should I try this, and what do they look like and where are they located? Maybe the Seafoam trick, where you dump a little into the brake boosters vacuum line might help. I am still open to suggestions.

One other thing, if my check engine light has never come one, could there still be codes stored in the computer?

Thanks again.

intel_guy

I have a 99 4.8L with the exact same symptom. It does not do it every time, and sometimes does it even starting the motor warm (like when I'm out at the store). Haven't really looked too far into it yet, but I plan to this week.

intel_guy

I do notice the battery gauge fluttering low when it happens. I bought the truck about 2 months ago with 126k miles on it and am wondering if it was flooded (no history of that on carfax). There was a lot (1") of caked dirt inside the rear wheel well and dirt/grass inide the bumper which I did not notice when I picked the truck up.

bwforum

intel_guy,

Mine actually seems worse when the motor is warm, like if I park for 20 minutes during lunch, then go. Sometimes it is so bad, I hesitate pulling out into traffic, fearing that I might not get up to speed soon enough. I'll have to check the voltage when it is doing this, thanks for the tip.

jethro_3

So are you sure it is not a manifold leak?????

__________________

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Cam in and Low 14's happening at the track

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bwforum

No, I have no idea if it a manifold leak or not. How do you test for it. Will WD-40 sprayed around the manifold with the engine running show up as an RPM increase/decrease? I don't know the symptoms of the leaky manifold problem, but I would be surprised if the chugging/hesitation would go away as instantly as it does. It is just like you flip a switch...it is cough, sputter, chug, then bam it runs like a top and doesn't do it again, until it is shut off for a little while and restarted.

intel_guy

Oh yeah...one other thing I noticed when it started happening is my SES light came on and gave code for Random multiple cylinder misfires. Could be the plugs???

Faze3

Damn, I'm clueless at this point. I'll have to defer to someone who knows more than me.

Sorry!

dcountiss

Have you checked your fuel pressure at start-up? My fuel pump went out on my 2000 Tahoe a while back, it was putting out around 20 psi instead of the 65 or so that it was supposed to put out. When I would start it, it would stall and sputter until it got past around 2500 rpm's for the first time, then it would run just fine. It turns out that it was taking the fuel pump that long to catch up with engine demand. After the new pump went in, it felt like I had a new engine.

bwforum

Is there anyway to check fuel pressure, other than bringing it into a shop? Labor is way too expensive, besides, I enjoy fixing stuff myself.