1999 Tahoe Misfiring
 

I own a 1999 Tahoe with a 5.7L with 100,000 miles on it. I have been experiencing a misfire after the engine gets up to operating temperature. I then took it to the local Chevrolet Dealership for a tune-up and made them aware of the misfire. They completed the tune up, check the OBD and found no codes and said that they road tested it and could not get it to misfire. I can really tell the misfire when pulling a car trailer. The exhaust echos off of the trailer and it can be heard quite clearly. The misfire could be heard through the right tailpipe. The Tahoe has true dual exhaust. Items that have been replaced during the tune-up and afterwards: distributor cap, rotor, coil, plugs, plug wires, fuel filter, air filter, battery and intake gaskets. I did a compression check and All cylinders are 115 to 120. I even took the truck to the muffler shop to check and see if it could be a baffle in the mufflers...NOT...they did put a balancing tube in the exhaust so now the misfire can be heard in both tailpipes. The power does drop off a little during misfires. I think that about covers it. Any suggestions would be greatly appreciated.

RE: 1999 Tahoe Misfiring
 

Have you had any work done on the upper engine where the upper (plastic) intake manifold may have been disturbed?

We see this sort of thing when injectors are installed in the improper positions.

RE: 1999 Tahoe Misfiring
 

I'm interested in this thread as well. I have a '99 Tahoe, 5.7L, with 115K miles. Recently the intake manifold gasket failed. I had that repaired and also had the distributer cap replaced, new plugs and wires. I now have an engine miss. The misfire is like a rumble at low speed when the engine is cold. Once the engine comes to operating temperature, the miss seems to happen at speeds ranging from 40 to 60 mph. It feels and sound like a thunk and its easily reproducable when accelerating and quickly getting off of the throttle. I took it back to the shop and they want to charge me $400 to replace the injector assembly. I haven't had anything done yet so the more information I can get on the injectors would really help.

RE: 1999 Tahoe Misfiring
 

I did have the dealership relace the intake and gaskets about a year ago. The misfire was there before and after this was done. I have been told that it could be the MAP sensor. Also...after replacing the distributor, rotor, coil, plugs and wires....I had a mechanic check the plug wires with a neat little tool that looks like a pen. You clip it to a plug wire and it will flash as current passes thru. Well...at idle the light will flash somewhat steady but as soon as the RPM's come up the flashes become very eratic. Almost looks like a plug wire is breaking down. Again..these are new wires. This misfire is at engine operating temperature and under a load. I know with 100,000 miles on it this may be a sign of things to come but this Tahoe has been a very good vehicle and I don't have any urges to get rid of it.

RE: 1999 Tahoe Misfiring
 

Normally an ignition misfire will trigger a DTC (light and store a trouble code); this leads me to believe that your problem may be fuel delivery related.
I will list a few things below that address this problem (in no particular order):

1. A deposit build-up on the CSFI poppet valve (injector) ball and/or seat may cause the poppet ball to operate improperly or stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis-fire condition. To correct this problem a professional injector system cleaning should eliminate this, I have also added 4 bottles of Chevrolet Techron fuel system cleaner to a single full tank of fuel and done this on at least 3 consecutive fill-up's with good results afterwards.

2. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit, this repair is spendy.

3. Have the dealer make sure that your VCM has the latest Service Calibration installed, (Calibration Part Number 16241012) would cause engine surge on 1997 models, the bad part # is 16232744 for 1999 models

4. Check all ECM and Engine Wiring Harness Ground straps for corrosion.

RE: 1999 Tahoe Misfiring
 

The dealership cleaned the injectors during the tune up. I often put a bottle of Chevron Techron fuel system cleaner in every month. I will try this again with the next fill-up. I'll check the ECM and wiring harness grounds. I'll check with the dealer about the VCM and the Service Calibration. As for the MFI...I'll wait on that. I'll let ya know what happens. Thanks!

RE: 1999 Tahoe Misfiring
 

Misfires are common on these engines with most aftermarket dist caps. Use DELCO or Napa premium(brass contacts)

RE: 1999 Tahoe Misfiring
 

Under the GM dealership franchise and SPO agreements you would expect that the Chevrolet dealer performing the tune-up would have used a Delco dist cap on a GM built vehicle.
If the Tahoe had a miss-fire when you took it in and still has a miss-fire after changing out those parts I would look to a different source for the trouble, especially since a distributor cap based miss-fire will trigger a DTC 99.9% of the time.

im having the same problem, no codes poping up and miss fire on cyl. 4. even tried a gm cap and rotor with no results, i did plugs, wires, cap, rotor, coil, fuel pump and filter. my lights also dim when it miss fires and its crazy cause it only started missing firing over 40 mph

My dad has a 98 gmc 5.7 and his was doing the same thing. After many replace parts, I finally put another set of intake gaskets in. Problem solved

so it was a upper intake leak? i found that intake leaks, bad distibutors (teeth) or sticikng valves from dirty injectors seem very common on these engines

Intake leaks are very common on the 5.7 vortec. My dads was leaking at the lower gaskets between the intake manifold and the heads

I have a 99 5.7 with 170k miles that has a major problem with misfires when cold and under load. The DTC code is always #4 cylinder. The vehicle actually bucks when this happens and it takes a few seconds for it to calm down. I have changed everything and checked the cam retard angle only to find it at 0-degrees. This does not happen once it is up to operating temp.

po303 misfire, need help
 

Hey guys, I haven't posted anything lately but I got another Tahoe and yes I'm glutting for punishment but what can I say I love the Tahoe. I just replaced my intake gasket due to antifreeze pouring into my oil and I knew I needed to do the spider update. I was trying to hold off until after Christmas but it didn't hold up. About a week before Christmas, I was on my way home from work when I noticed that my temp hand ran up to 210 and I was thinking maybe I need to stop and check my antifreeze. I did and it just wouldn't fill up to the top of the radiator and I limp it home. It got up to 230 and wanted to cut off so it did and coasted home to my driveway. After it cooled down I had to get it up my driveway I added water to it. I then pulled the oil dip stick and OMG milk up to the top of the stick. Well, I have another tahoe that I had put the new updated spider on and never got it inspected for the emission requirement for NC. So it was just sitting in my side yard. Good news it that the other Tahoe engine had started knocking the week before when I had moved it. Now it's become the parts vehicle, so there is my new spider that I had put on with all the new parts. So, I went ahead and yanked the intake off of both Tahoes and fixed it to the 99. The 99 started a few months ago with po303 and 174, 171,131,151 and the all famous po300. Well since I was doing the intake and I was watching it as I had it all back together I knew that the O2 sensors were shot. I just replaced the 2 pre converter o2 sensors I found a fuel line with a hole in it. I did smell fuel for a couple of months but I was thinking it was the spider. So, parts Tahoe got robbed again. Now I have been getting the po303 since the spider change. Tonight I ran the seafoam trick and it didn't fix my problem. I connected my timing light and noticed that number 3 was firing and then it would stop hence my misfire condition. Now I'm looking for any new ideas, I'm going to check the dist cap tomorrow which the cap came from the parts Tahoe that only ran for maybe 120 miles. I am also going to change out the control module and ignition coil. Any other ideas I might be missing. Thanks in advance. Jerry

Update
 

Hey guys, just a quick update to my issue with my 1999 Tahoe and my po303 misfire. About 2 weeks ago I took it into my local Chevy dealer and they gave me some of the worst news I've ever had with the Tahoe. They took it into the bay only to come to me that I had a burned valve on the cylinder number 3 that was the cause for po303. I wasn't going to except that for my cause for a misfire and I was running out of time due to vehicle inspection being due. I did another tune up with cap, rotor and finally wires and plugs. I kept checking with my ob2 scanner to see if my ready codes were set and ready for inspection but never ready and kept getting po303. Well, I finally checked this evening with my scanner and all my ready codes and now I can get my inspection tomorrow. I just wanted to share with you guys. All of this started after I did my spider upgrade and intake gasket. I found during the update on the spider I found a fuel line leaking, that had been leaking for a couple of months. I hope this helps....