MWRacing

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.

ZX1100F1

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.

f7cat

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.

MWRacing

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.

ZX1100F1

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.

MWRacing

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!

shaight

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

ZX1100F1

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.

ackley

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

bdburb

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