Hey guys, I have an 84 CJ7 w/ 258 Carter BBD and T-4. It has the TFI upgrade and the Nutter bypass. The motor runs very well at idle and at constant rpm, but when I accelerate it bogs / stalls until the rpms finally catch up w/ it then it runs great. I can put the pedal to the floor (In any gear) and slowly let the pedal back up to about 1/2 and the motor seems to catch back up.
I was wondering what tests I can perform to see if my problem lies within the fuel or the spark? I was trying to avoid just replacing parts until I get the right one. I have the timing set at 9 degrees BTDC.
That is my guess. The accelerator pump gives the carb a little extra squirt of gas when you accelerate quickly. When the engine is turned off you can hear / see it squirt as you pump the pedal. It is also adjustable if you need to have it provide more fuel. Another idea is fuel filter or fuel pump.
I would first unplug and block with a bolt, the EGR line to see what happens.
A dirty gas filter can cause that, especially if it isn't in right side up. It has 2 outlets, the center one goes to the carb, the 'top' one goes to the return line. The return needs to be up top or gas can go back to the tank too easy and can syphon empty causing long cold starts.
Did you port the timing advance? I would use a light to see how the advance works while revving it. Sometimes folks forget to oil the felt pad under the rotor that keeps the timing advance plate moving and it seizes.
How about gas octane? Too much alcohol in the gas will make them run like crap.
Could the carb base plate have gotten flipped so you don't get manifold vacuum routed up into the carb like it is supposed to? The cut outs taper out and up to the carb. Just a thought, have seen that one before.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Thanks guys for the suggestions. When I purchased the CJ 04/04 it was hard to crank when it was cold and had some sort of miss in it that you could easily hear when it was idling, but driving it at highway speeds it had plenty of power and no hesitation when I accelerated but it did ping in 4th gear when under a load. I decided to give it a tune up because I wasn't sure when the last time it had one. I put a new dist cap, rotor, plugs, wires, fuel filter (return line is at top), and had the original carter rebuilt. The miss when it was idling or pinging didn't go away, but it still drove fine after it warmed up so I decided to leave it alone since it was my second vehicle and I only drove it on the weekends.
I have since sold my primary vehicle and decided to make my jeep my daily driver which was about a month ago. I decided I wanted to go ahead and get the motor in great shape and do some mods / upgrades on it that I have read about since I have owned my jeep. I started w/ wanting to get rid of the miss and pinging I kept hearing so I went and did some research and decided to do an ignition upgrade to the TFI set up, set the timing to 9 degrees BTDC @1600rpm, changed from manifold (base of carb) vacuum advance to ported (side of carb), and It worked like a champ, and voila no more miss! I then wanted to do the Nutter Bypass (since I have heard nothing but good things about it) and did it and voila no more Pinging!! However, it was at that time that I could tell a faint acceleration issue when I pressed it all the way to the floor, so I thought well that's just this old carb and I'll go out and buy a new one. I decided to get one that didn't have the stepper motor on it from a 79 CJ (had to change base plate) put it on, and the jeep still idled fine, but the acceleration issue was worse I adjusted the 2 air mixture screws on the baseplate and got it a little better but still was not good at all. I put my old carb back on, adjusted air mix screws, and then it was a little better than the new carb but not good at all. I went ahead and changed the fuel filter again yesterday and still the same thing. I now am having to shift from 4th to 3rd to go uphill (I didn't before). It's like the rpms haved changed. I did hear it mildly backfiring when I downshifted yesterday so maybe the timing is off still? Do I need to retard it some more? The EGR valve has been plugged since I have owned the jeep, and since it ran so well before I started modifying then I wouldn't think that was it. It's like I've fixed a few problems only to discover a new one. Could I be getting too much spark since I'm putting out more volts from the new coil? Would you adjust the float level or Accelerator pump? I'm not sure still where to start. Also, I am using bosch platinum plugs gapped at .045 for the TFI setup. Sorry this was so long, but I wanted to make sure you knew the history.
You know I never thought about that sticker being for the ford emissions computer, and I just set it at that because I read when I setup the TFI to set it at 9 degrees and looked at the sticker and it said at 1600. So you would recommend to set it at 9 degrees BTDC with vacuum line off at idle or somewhere around this? Yes, I set mine at full advance then. Nice. Thanks again for all you help.
You know I never thought about that sticker being for the ford emissions computer, and I just set it at that because I read when I setup the TFI to set it at 9 degrees and looked at the sticker and it said at 1600. So you would recommend to set it at 9 degrees BTDC with vacuum line off at idle or somewhere around this? Yes, I set mine at full advance then. Nice. Thanks again for all you help.
Your mileage may vary. I use 91 octane gas running at 9 as a base and only get a slight rattle when pulling up a long hill too slow for the gear. If I remember right one YJ ran sweetest at 7 and one other at 8.
With that combo, I get 23 US mpg.
If I drop the timing down and try to run regular gas, the power sucks the big one and my mileage drops to 15 mpg or so.
I have the original owners manual and in there it even calls for high test gas to avoid ping when running hot and hard or it says to lighten the load and slow down... This is with the computer and knock sensor working even....
I figure running with the hard top and hard doors on and full of camping gear at 75 mph as pretty hot and hard so.....
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Thanks Mike, I'll set the timing again tonight when I get home and let everyone know how it went. That's about right on the mileage. I put in regular gas and I get about
I re-adjusted the timing to 8 at idle, and it is running like a bat outta you know where right now. However, it has the pinging again. Any suggestions there or should I start a new thread? Thanks to everyone for helping me with this! It's SO nice to have my Jeep back!!
There are two fluids that work well, one is ATF, the other is apparently water. I only have first hand experience with the ATF and that makes the insides of the cylinder in brand new clean shape. I have been told by a 'lot' of folks that the same amount (one pint) of water will do the same.
You take a hot engine, open the air filter and with your hand on the throttle to keep it above a stall you 'slowly' trickle the fluid into the carb. Go very slow and keep the revs up so it doesn't stall. Once the fluid has all gone in and the smoke has cleared so you can see the ground again, you are good to go.
The ATF 'will' put out massive amounts of thick white smoke, so warn your neighbors first or you are likely to see fire trucks coming... ;-)
The water apparently doesn't smoke at all but does the same job if poured in the same way.
When do you see the ping? Do you get any run on at all when the key is shut off?
I do see a ping if climbing a long hill at say 60 mph in 4th gear. That is a normal load ping and is acceptable. It is telling me I really should be in 3rd for that speed and load range. (for my 3.31 gears and
33" tires, it is telling me correct)
If I hit the same hill at 70 mph in 4th, no ping. I tried my timing at
5 or 6 because of overheating and the ping was gone along with the power. My overheating was a water pump with a slipping impeller.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Well I think it's back going good, even with the appropriate ping. I filled it up today w/ 93 octane and there is no ping any more except when I am lugging it uphill in too high of a gear. There is no run on when I shut the key off, so apparently the timing is good. I am going to go ahead and try either the water or the ATF idea to clean up any carbon buildup I might have, but other than that I'm just going to enjoy driving it! Thanks again Mike, you've been a big help! Chris
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