I was wondering if anyone has had this issue ,after i installed the updated mpi spider fuel injection system the truck stumbles slightly off idle when accelerating !!! I installed a new cap and rotor (ac/delco of course) also i replaced the plugs with the recommended plugs!! Its not that bad but kinda annoying !! I thought maybe a vacuum leak ??? I will check that when i get a minute !! any ideas???? Thank you!!!

 

I forgot to mention that i no longer have spark knock with regular gas !! I was running midgrade and premium to avoid that !! $$$$ costly!!

 

You didnt mess with the throttle stop screw, did you?

BIG No-no!

And I assume you didnt mess with the distributor. So maybe just needs to relearn. But it does sound a lot like a little vacuum leak.

 

No i didnt remove the distributor or mess with the throttle stop screw !! it runs goods i wish the idle was a little smoother but i know these 4.3 motors are rough runners!!

 

vac or air intake leak after the mass air sensor. like o=ring on air intake at tb? vac hoses vents look it all over. i suspect more a leak before tb than anything. remember if the engines using air the mass air isnt detecting itll run lean and hesitate. check that vac tree by the pcv valve too, the one that turns into the upper plenum with a 1/4 turn make sure u put the o ring on it (the brake booster hooks up here)

 

???? They are? Cant prove it by me. What are you comparing it to? And what is your idle rpm?
Can you see the engine move at idle.. or feel it? Another symptom of vac leak.

 

I will have to check for leaks !!! i think your 100% right on that!!!

 

From what i have heard the balance on these motors give them a slighlty rougher idle!! The idle is like 600-700 rpm!! i do feel a rough idle but it doesnt feel like a misfire and runs great when your rolling !!! it seems to be getting better gas mileage (slightly) i will know when i fill it back up!!! I did not replace the pcv valve to intake o ring , but i will now....

 

i think not understanding, of course check everything. but main concern imo is the big 4'' oring on the plactic air horn on top of the tb going to thr air cleaner. check it all but if runs ok and just hesitates then i would look first for a leak between tb and mass air sensor,making it lean and hesitant

 

Thanks i never thought about the tb to air cleaner connection i just assumed it was never gonna leak there !! i will check that !! by the way i just checked and i got 17.5 mpg about the same as i was getting with the old spider!! but if i can find out what is causing the stumble maybe that will help mpg!!