Misfiring or stumbling under light load

[laxman21]

99 burb. 175k.

Started to stumble at highway speed with light gas pedal. Runs fine when under heavier load.

plugs, wire, cap rotor all about a year old. This fixed it when it was doing it before.


Mechanic thinks it the spider injector because he gets some black smoke out of the pipe when accelerating. Leaking extra fuel into cylinder.

Any other suggestions or should I just replace the injector with the updated one?


Edit: no codes or SES light


Should I opt for the cleaning before replacing route?

[j cAT]

Originally Posted by laxman21

99 burb. 175k.

Started to stumble at highway speed with light gas pedal. Runs fine when under heavier load.

plugs, wire, cap rotor all about a year old. This fixed it when it was doing it before.


Mechanic thinks it the spider injector because he gets some black smoke out of the pipe when accelerating. Leaking extra fuel into cylinder.

Any other suggestions or should I just replace the injector with the updated one?

Edit: no codes or SES light

Should I opt for the cleaning before replacing route?

check distributor ,,,when bearing goes bad rotor wobbles..

if if starts and runs good at idle the fuel should not be a problem..

black smoke on throttle increase usually ignition ...poor spark,,,at the incorrect time...

[laxman21]

Originally Posted by j cAT

check distributor ,,,when bearing goes bad rotor wobbles..

if if starts and runs good at idle the fuel should not be a problem..

black smoke on throttle increase usually ignition ...poor spark,,,at the incorrect time...

Will check.


Remove cap and check to see if there is play?

[Jeremy-WI]

Have the mechanic hook it up to a scanner and check cam retard, it should be 0 degrees +/- 2 degrees. If it is -5 or more negative, pull the distributor and check the gear, it could need replacement

[laxman21]

So how doies the wobble look

[j cAT]

Originally Posted by laxman21

So how doies the wobble look

hard to tell.....try to get a look at a new one to compare,,,,or go to a scrap yard to check a few..it looks like it does move alot..

how does the cap /rotor contacts look...is the metal distorted where the rotor rides..

[777stickman]

The service manual says there should be no noticeable rotation in the rotor. It looks like you may have enough rotational play to cause your trouble.

[ken_man_1]

I just went through this distributor stuff on a 99 gmc 5.7, and that is what my new gear looked like. The left to right movement should also move up and down as well. The gear is spiral - thus the up/down and left to right movement. They have a little play - and from what I can see on the movie you posted, mine looks the same.

Another little thing to check (since you have the cap off)... Take a wrench and put it on the crank bolt. Move it slowly back and forth and watch the distributor. If it moves pretty fluidly, then more than likely your dist gear is okay. That means that your timing chain is pretty good still, as well. But if it is jerky, then you need to investigate the reason for jerking.

I had to pull the distributor in mine cause the gear was so worn, that 3 teeth were missing. It ran like crap for months on end (this is a plow truck only) until they put me on the job to fix it. It was only under heavy load that it failed tho. Light load was no problem.

I've read somewhere that the fuel pressure regulators like to leak on these trucks. Unfortunately in order to find that out, you need to pull the plenum. However, it's usually easy to spot because underneath the mount for the regulator, it's nice and clean. It it's not leaking, it will normally be pretty dark or black even.

Hope this helps m8!