TFI is it all it is cracked up to be?

[DerekC]

What was the last year for cherokee to have the 2.8 gm engin

I did the TFI swap yesterday, wanted to do something OTHER than the freeze plug that is leaking...maybe this weekend on that one. Anyway, yeah it does seem to smooth out a LITTLE better. I was really hoping for more though. Still hard to start. I thought maybe the carter crapcarb. i know alot of guys do the idle tube cleanup but to be honest, my rig does not run bad after warmup and does not sputter ect at idle...after warmup. It does run REALLY rich ALL THE TIME and gas mileage is in the tub. new plugs ect with TFI swap timing is on the money...any input is welcome.

-D-

 

[GaryMB]

RE: What was the last year for cherokee to have the 2.8 gm e

Does the carb have a stepper motor? If so, my best guess is something with the emissions system...the emission system works the hardest at warmup. Also, how many miles are on the carb? I would pop the hood and watch the choke as the engine warms up. There is also that pnuematic/electric choke thing on the drivers side of the carb. As for the TFI, I imagine dirty spark plugs could take away some of the extra spark.

 

[lah2420]

Re: RE: 2.5L question

I noticed a small difference with the TFI. Not really enough for the money though. I'm running a Weber right now too. Mileage and starting are no better than with the Carter. Maybe even worse. I'm considering trying the 2100 swap to see if that helps on the starting.

 

[Inspector-Gadget]

RE: some pics of the stuff on

GaryMB wrote:

...the emission system works the hardest at warm-up

Gary, I must respectfully disagree. I would state, to the contrary, that the Carter BBD emissions system works the least during engine warm-up.

Why?

The Carter BBD stepper motor and the associated emissions control computer are not active until such time as the engine achieves normal operating temperature.

As I understand the operation of the steppered BBD and associated controls, the sequence of startup events with a cold engine goes something like this.

(1) Ignition key to “On.”
Computer powers up in “open loop” mode (because of cold engine) and centers the BBD stepper motor controlled jets. If you watch the BBD needles at cold engine key-on, the BBD needles go all the way forward, then retract to center and stay there.

This action is analogous to an “ink-jet style” computer printer hunting for and finding the “home position” for the print-head on printer power-up.

(2) Cold engine started. The BBD needles do not move because the computer knows from sensor input that the engine is cold. Engine air-fuel mixture variation is controlled primarily by the automatic choke during the warm-up phase of engine operation.

(3) The running engine eventually achieves normal operating temperature, and the automatic choke butterfly is fully open. The emissions control computer is notified of engine normal operating temp via sensors. Only then does the computer go into “closed loop” mode and take over active, real-time positioning of the BBD stepper motored needles.

The BBD needles will now change position constantly under computer control as the feedback system monitors the exhaust stream (and other aspects) of the running engine

In short, assuming the emissions control system is totally functional, the BBD and associated computer play no part in cold engine operation beyond setting an initial and fixed air-fuel mixture.

That said; I could be wrong. Perhaps my understanding of the system is incorrect. Nevertheless, that is my take on the Jeep 4.2, I-6, Carter BBD emission control system operation.

I should also state that I deliberately omitted the actions of several other things like the air-cleaner air intake flap and yada, yada to keep my discussion centered on the actions of the Carter BBD and emissions controls.

Regards,

Gadget

 

[DerekC]

Girl doing jumping jacks

I must confess, I am new to my CJ and look forward to our relationship. that said, I know the smog pump is not working ( the belt is off )And is there a computer on the 80 model? I have been under the dash and not seen one. I am a Toyota tech, but my expirience with carbs is little. Why not remove the emmisions system totally? I know it is illegal and am not asking for endorsement to get anyone in trouble, but if it were removed all together???As for emissions at startup, gotta go with Gadget on open loop vs. closed loop, but that again infers there is a 'puter on my rig. more discussion and input is welcome.

-D-

 

[GaryMB]

The computer on my '84 is to the left of the glove box under the dash, sort of sandwiched between the heater and some other componet. It's pretty small. If you have an '80 though, you don't have a stepper motor, and i dont know if that means you have a computer or not. I've been told that removing the emissions system will increase performance and hp, though i can't vouch for that since my jeep has never had a functioning smog system during my ownership . I does make sense though that some of the emission things don't help performance, like the egr and catalytic converter. The smog pump does take a few horses to turn, too.

 

[DerekC]

RE: rear end

Ok no stepper motor, one less thing to factor in. Will peek in locale you said for 'puter, do not think I will find one(hope and pray.) thanks for the info.

-D-