q-jet tuning

[diesel4me]

dies under load??..

I've had bad rotor and distributor caps cause an engine to run OK in neutral ,but crap out and stall,stumble,and backfire as soon as I put it in drive..they had "carbon tracks" in them,that let the spark jump to ground,or to a different cylinder than the one that was supposed to be fired!..I went koo-koo chasing this problem,and replaced a LOT of things before I changed the cap and rotor (they appeared to be perfect to my naked eye,but evidently had SOME problem!)..seemed to act up more on rainy or damp days..

A defective ignition module can cause backfiring and poor performance under load too..pick up coils too!..many times they only act up intermittently,and are hell to diagnose...replacement is the best "test",especially if they are old or original..The ignition coil may have a crack,or low output..poor spark will blow out under load,and that can cause the same symptoms....


AC-Delco modules are the best ones--dont be cheap when it comes to the module!--I've learned many "cheep" bargain brands lack the dwell advance curcuit,and not having one really robs power and mileage...they fail easily too..I get ribbed for robbing used GM modules from junkyard cars,but I've never had to walk home because of one yet..

 

[az-k5]

Cap is new and has a new module on top. The guts are a bit dirty (as mentioned). Been playing with it and it is getting better. Still a bit of a stumble and backfire. Some of it might be my getting used to the truck manual and I think I found an exhaust leak.

 

[az-k5]

Figured out most of it. Played with it for a while (adjust a little - drive, adjust a little - drive, repeat) and got it semi normal. Drive fine backfires a bit when letting off. I found two things. The mufflers don't have enough back pressure (pretty old) and the P/O put in Bosch platinum plugs. Well those don't work for crap. Then with the rich fuel issue and lack of timing an already crappy plug fouled out. I can punch it if it hits on certain cylinders so I am pretty sure it is down to a plug issue. I am gonna put some AC Delco truck plugs in and be done with it (I know they work, they fire in oil in the truggy).

Thanks all for the help.

 

[pauly383]

TJ didn't like the Bosch either . I took a chance and tried the Bosch with the multiple tips , and so far so good . But it just feels all weird inside me not using Delcos , or Autolite 145's .

 

[diesel4me]

toss those plugs!..

We've had several chevy's come in my friens shop that had those cursed Bosch spark plugs..as soon as we put AC plugs in,the cars ran way better---he now refuses to install Bosch plugs in GM vehicles, if customers bring them to him--they only seem to work in some applications specifying platinum plugs,mostly on Fords..Chevies dont like them !--we've seen several GM motor SKIP when we put in Bosch plugs--like they had a "dead" cylinder!..one customer refused to pay him,said his car was WORSE after we "tuned it up"..we put the OLD AC plugs back in,and it ran great!...we tore our hair out before blaming the "new" plugs too..wasted a lot of our time!..

 

[az-k5]

Aaaarrrrrgggggg!!!!

Got the plugs changed. It runs better. Heck I could drive it all day but if you get on it at the wrong time it backfires and spudders like mad. I have played with the APT, idle and timing. Just can't get it to hit the sweet spot.

Is this just one of those things you have to minor adjust -> drive -> repeat?

I can feel it is so close to perfect. It is 1000 times better than when I brought it home.

 

[pauly383]

Its gonna kick your a$$ . But in the end when you can play with it at will , and adjust it from driving nice to passing emissions every couple years it will be worth it .

I spent several days driving , popping the hood , counting turns .

You may want to do yourself a favor , and pull those probably not working vacuum switches off , and run EGR and spark straight to the carb . If it looks nice and the required stuff is there , they don't care as long as you sniff good .

 

[az-k5]

Yes the vacume switches are not working. I figured that out last night. That accounts for the high rev release backfire. Now to figure out the mid throttle backfire under load.