Bogging at lower rpms
 

Just the other day my Suburban (350 TBI/ 700R4) developed a bog at lower rpms. First noticed it at a stop light. From being stopped and idling until about 10 mph(don't have a tach to know the rpms) there is a serious bog down happening. Once past the 10 mph, it accelerates like it always has. Also, I notice a slight bog when the tranny upshifts to the next gear. Ie: I am accelerating in third, and it shifts into OD and after the shift when I am first in od there is a bog there. Basically does this at the beginning of every gear, but by far, the worst is from a stop.


What should I be looking for? Already tested the egr as it popped up in a lot of posts causing a bog down.

Re: Bogging at lower rpms
 

tps

Re: Bogging at lower rpms
 

TPS tests as good at .747v at idle and 4.37 at wot

Forgot to put in the first post, this problem does NOT occur with the truck in park. Only happens when under load in gear.

Also should add that, I, once every couple of months get a code 32 which is supposed to be an egr problem, but the egr itself is good. I seem to get the code after a long period of consistent throttle, ie doing a perfect 45 for like 10 miles without changing speed at all. I however did NOT get this code since I have had the bogging problem.

Re: Bogging at lower rpms
 

whats the injector spray pattern look like

Re: Bogging at lower rpms
 

Still having this same problem. The injector pattern looks good. I recently started fiddling with the timing in a effort to stop this problem. I used to run the truck at 0, and I worked my way up to 9. It's definitely picked up more mid range power, and the bogging seems to happen less often. Say 75% of the time, vs before where it was like 95% of the time. I don't know if I should bump the timing up anymore, or what. Ideas?

Re: Bogging at lower rpms
 

Check all of the plugs and wires? Look for burned/melted/corroded boots on both ends, etc?

Re: Bogging at lower rpms
 

Keep forgetting to put this in here:

The bogging seems to go away if I sit and idle for a bit before trying to accel. Ie: going thru a fast food drive thru, when leaving it seems to be more willing to take off from the line like is should. Fuel pump weak maybe? The idling allows it to build up pressure to the correct amount?

Re: Bogging at lower rpms
 

I would check to see if the torque convertor lockup switch is working properly.

Re: Bogging at lower rpms
 

Switch in the tranny is less than 6 months old. Had a problem with it, and during the time the switch was bad I had a toggle switch to turn it off completely, let it control on its own, or lock it in place. With it turned off completely, I still had the problem. Could the converter be able to lock up funny even with the switch disengaged?

Re: Bogging at lower rpms
 

So, I've got a new fuel pump now. So fuel pressure is definitely not my issue. However, I was going over my datalog again, and think I may have discovered my problem. It seems that the knock sensor is picking up a lot of knocks at idle during the times where it won't accel nicely. But then when it does accel nicely, the knock sensor picks up at most 1 or 2 knocks in a several minute period. I am going to datalog again today to confirm this. I realize knocks (or what the sensor believes are) are very hard to diagnose. Anyone have any ideas on why I could be getting knocks sometimes, but not others?

Re: Bogging at lower rpms
 

huh.....I just realized that ole stich got the boot!