Lack of power first minute after startup.

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.

throttle body may need cleaning

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

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


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.

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.


See my post here:

http://www.automotiveforums.com/vbulletin/showthread.php?t=384839&highlight=throttle+body

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.

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.

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.

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,

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.

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

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

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.

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,

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.

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

Sorry!

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

Sorry!

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.

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.

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.

There is a service port on the fuel rail to connect your fuel pressure gage. Like I said before, mine was running around 20 psi, I think the spec is 60-65.

There is a service port on the fuel rail to connect your fuel pressure gage. Like I said before, mine was running around 20 psi, I think the spec is 60-65.

Thanks dcountiss, I'll see if I have something that will connect and check it.

i'd pull off the cap and rotor from the distributor and see if theres any burn markings or anything like that (its a little hard to get to) it could be a number of things like , 1-2 cyclinders not getting the a good spark causing a sensor in who knows where to read wrong etc. I'd try the basic though, check fuel pressure, check condition of cap and rotor and spark plug wires (easy to replace if needed), check the pvc valve (helps control idle like $3 for a new one at napa).

My 99 4.3L would kinda do the same thing , it would run fine for awhile , then sometimes it would hesitate starting up , or not start at all. Brought it to a garage who replaced fuel pump and a few other things and still didnt fix it. I eventually found out that there was a very tiny nick on a spark plug wire causing it to die down when it hit the engine block, but also the pvc valve had some dirt in it causing it to run rough at start ups

its a little hard to get to the distributor because it doesnt have one...

i think you have a fuel pump going out or a vacuum leak..... good luck i hope you find out whats up with it...

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.

Well, I checked my fuel pressure, and as soon as I hit the key, it jumped to 55 psi. and didn't change much at all after running for a bit. Instead of bringing it into a shop, I picked up a fuel pressure guage from Autozone for $36.00. I can't imagine that is as accurate as the ones in the shop, but I figure it is close enough to see a problem that will cause the chugging problem that I have. Anyone have any idea if +/- 5 psi. would cause this problem? Thanks.

no it shouldnt.....was it running rough when you got the 55psi reading???

no it shouldnt.....was it running rough when you got the 55psi reading???

It was running fine, but it doesn't typically misfire when it is idling anyway. I'll have to try it again, and have the wife powerbrake it this time when I am checking it...I hope she doesn't run me over!

jack up the rear end

no it shouldnt.....was it running rough when you got the 55psi reading???

I checked my pressure again, actually a few times. It is usually right in the 48-52psi range. While checking it, I pulled the vacuum line off of the fuel pressure regulator and it jumped to 58psi. I would be interested in trying to drive it around a bit with this hose unhooked and plugged. Will I cause any damage running it like this?

Even though you already replaced the fuel pressure regulator, are you sure the replacement regulator is not bad?

Marmot

Well, I have been fighting this for awhile with no luck. I had it to the shop and they put the scan tool on it. There are no trouble codes, and there is nothing that they could see that would be causing the problem. I had a fuel pressure gauge hooked up, and drove it while watching the gauge. The pressure stayed the same, whether it was stumbling shortly after startup, or I had driven it for awhile. Another person in this forum has the same problem, but I didn't see any resolution. I am baffled. Any help?

The other forum can be found here:
http://www.automotiveforums.com/vbulletin/showthread.php?p=2442274

i have the same problem and i have no idea what it is

i have the same problem and i have no idea what it is

I had my truck to the GM dealer tonight, and I think I stumped them. I told him what the fuel pressures were, and he said they were in range. I told him everthing that I checked and tried so far. He hooked the scan tool to it, and while it was running, the MAF senson seemed to be out of range a bit. He said that I could try and clean it with brake cleaner, but no guarantees. He applied a computer update (Bulletin # 010604006), but it didn't help at all. I'll try and clean the MAF sensor tomorrow and see what happens, and I will let you know the results.

Well, I cleaned my MAF sensor, and it didn't make one bit of difference. I have a question though. If it was my MAF sensor causing the problem, and I unhooked it (which I already did) and it didn't seem to have the hesistation anymore during the first 30 or so seconds, would that be a good indication that it is causing the problem. Any other way to diagnose the MAF? Thanks.

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 one. It solved my problem, and my truck once again runs great.

Wonderful! glad you're rolling again, and thanks for all the info.