under light load; engine misses

[Y2KpewterZ]

5.7 Vortec in OBS 2000 Z71 Tahoe. As title states, engine has a miss under light loads; such as casually taking off from a stop (like a normal person) or maintaining speed while going up an incline. The miss is faint, but still noticeable. Doesn't do it throughout the entire rev band either. Only in lower RPMs. If I accelerate like a pissed of 16 year old its fine, and doesnt skip a beat. I replaced the fuel filter with an ACdelco unit this past summer. I'm thinking it may betime for a tune up. Any other ideas before I invest in all new tune up parts? A buddy suggested possible egr issues, or a failing spider injection?

 

[2000tahoeZ71]

Could be any number of things. I would start with new ignition components if it has never had them. Use AC Delco stuff. Could be a spider. The new system is great but costly. Best to replace it when you are doing lower intake gaskets.

 

[OR VietVet]

No CEL? Like 2000tahoeZ71 said, if tune components are old enough start there first because if old enough then repair your problem would be by doing needed maintenance anyways.

 

[Y2KpewterZ]

Nope, No CEL. I will be using all ACDelco products as well.

41-993 plugs x 8 @$6.49 ea
9718Q wire set @$59.99
D465 rotor @$13.49
D329A cap @$59.49
D577 coil @$65.99

.. Am I missing anything here?

 

[2000tahoeZ71]

Everything looks good except for the prices and the plugs. The AC Delco R44LTS6 plug is the standard plug and is what I would use. Much cheaper too. Look on Amazon.com for the others. I just replaced my coil too and i think it was 25 bucks with free shipping with Amazon prime. However, compare amazon to rock auto as sometimes rock auto is cheaper on parts even having to pay shipping. Rock Auto is a drag sometimes because they will ship your order from 3 different warehouses charging you shipping from each one.

I see now where you have the AC Delco Iridium plug, those are fine too just more expensive. Amazon has them for 4 somethings a piece.

One final thing, now that I think about it my truck (identical to yours) had the same thing kinda going on. I don't know exactly what caused it but I noticed I was losing coolant, and the exhaust smelled rich. Then the CEL came on for catalyst insufficiency. I was burning coolant due failed lower intake gaskets which may have burned out my catalytic converters, or something was going on telling the computer to dump fuel to it which could have caused it. But with 178K on it at the time. I decided I was never going to get rid of it and ended up doing the lower intake, changed the spider out with the MPFI system, and put new cats and O2 sensors on it. Runs awesome now and has for a year. The only thing I wish I had done was change the distributor gear while I had it out as they are nylon and will wear out. However, when they wear out I believe they will throw a timing code due to the +/- 2 degree discrepancy. Not sure. My point being, if you plan on keeping the truck, and know it's never had lower intake gaskets now may be a good time to do it all.

 

[Y2KpewterZ]

I just replaced the cats in it this summer. Y pipe had a crack in it so I replaced it witha bolt on unit. Previous owner did intake gaskets on it already too. Not sure if spider injection was upgraded or not.. Any way to tell? Iirc if I take the throttle body off and look down, the lines will have a larger diameter, does this sound right?

 

[2000tahoeZ71]

The hoses on the MPFI will be clear/opaque covered by black heat shrink like stuff with wires going with it. Toward the end that goes into the intake runner there will be a electrical plug. There is a green connector on mine.

 

[SunlitComet]

Measure your ignition wire resistance and inspect your cap/rotor. The spark plugs on an obs vortec should be delco 41-993 or autolite xp605. Also ensure your wires have no burn thru and are completely seated on plugs and cap.

---------- Post added at 02:18 PM ---------- Previous post was at 02:12 PM ----------

The hoses on the MPFI will be clear/opaque covered by black heat shrink like stuff with wires going with it. Toward the end that goes into the intake runner there will be a electrical plug. There is a green connector on mine.

There is also a indicator in the body itself. When you remove the connector at top you will notice either small round or t-holes above each port. http://www.tahoeyukonforum.com/forum/showthread.php?t=31405

 

[Y2KpewterZ]

Measure your ignition wire resistance and inspect your cap/rotor. The spark plugs on an obs vortec should be delco 41-993 or autolite xp605. Also ensure your wires have no burn thru and are completely seated on plugs and cap.

---------- Post added at 02:18 PM ---------- Previous post was at 02:12 PM ----------



There is also a indicator in the body itself. When you remove the connector at top you will notice either small round or t-holes above each port. http://www.tahoeyukonforum.com/forum/showthread.php?t=31405

The connector at the top.. The large rectangle behind the throttle body? The comparison of the old vs new in the thread posted, the old pic doesn't work.

 

[SunlitComet]

The fuel injection connector harness. the body inside should look like this if it is the newer design.

The old ones IIRC had t-shaped holes instead of the round ones you see here with the white color in them.