bryzuky

ok been trying to figure out whats going on with my 94 GC , runs great at normal driving , starts up everytime like it should , prob i have recently started haveing is when i am going uphill and get on the gas ( enough for trans to kickdown into lower gear) it starts missing and stays like that for a little while even if i get off the gas right away then after a short time it will go back to normal , will even do it if im on flat ground and go to pass someone


have done the cap , rotor , plugs ( wires are fairly new so left those alone) plugs were super clean due to motor only haveing 114,000 miles on it and checked fuel pressure ( without motor running ) just with key on and pressure is around 45 and stays there also have changed fuel filter

im thinking it might be the TPS and that is what is next on my list to try

wonder if anyone can think of anything else that might be causeing this ??

Bustedback

I would take a second look at the plug wires and check the fuel pressure while the engine is running under a heavy load.

bryzuky

yea i was rethinking about the plug wires early this mornin when i went to bed , might be not giveing plugs enough spark at heavy throttle and higher RPMs to ignite the extra fuel

dave1123

What are your plugs gapped at? You may not have enough voltage to jump the gap at higher cylinder pressures. Low voltage, bad wires, and large gaps can all contribute to misfiring under heavy load. Unless you've got a plugged fuel filter, there should be enough fuel pressure. The only ways I know of to check pressure under load are to run a guage on a hose into the cab, or put it on a chassis dyno.

bryzuky

plugs are gapped at 35 , ill have to check the coil pack on it to see if its putting out enough voltage , and also i had something come to mind and that is it might be the fuel return diaphram that isnt closeing at high rpms going to do a vacume test on it lil later this morning and go from there i guess

Brambles

I had plug wires do that to me once, breaking down under load

bryzuky

yea i have had that happen on other rigs so changed them and wasnt the case , even changed out the fuel pressure regulator and no luck, so got mad and it and really started looking at it and found that the factory vacume line that goes up to MAP sensor had a crack in the elbow and was not geting proper vacume to it so changed it and seams to be ok now , but havent had a chance to really run it hard up the hills yet

Bustedback

That line to the MAP sensor is often over looked.

dave1123

X2. Many vacuum lines are overlooked. Often they crack with age and even the plastic elbows or tees can crack. Often the vacuum signal is not strong enough to cause an audible whistle and are hard to find.

Case in point; Years ago, transmissions had vacuum modulators on them. They are under the car and the little piece of hose that connect them would crack or get soft causing the transmission to not shift properly. People thought they needed a new transmission when a 5 cent piece of hose fixed it. I wonder how many people got stung by that one?

bryzuky

well still no luck, think im goin to run a fuel pressure gauge inside and see what it does when it starts to cut out on heavy pull ,

fuel pump might just not be able to keep up at higher RPMs i did notice when i had my gauge on it ( under hood ) the fuel pressure would drop a good 10 pounds when you nailed the throttle so idk , i would think it shouldnt do that

going to swap out the relay this morning and try that ( couldnt hurt to try lol )

zjrog

I recently had a similar issue. Had proper fuel pressure with no load. But had a similar issue a few years ago with an XJ and it was pump related. In my ZJ's case, it was infrequent, but becoming more regular. Swapped the pump and no problems in the last 2000 miles. Good luck.

bryzuky

yea i still think it might be the pump just not able to keep up , swapped out my map sensor and cam sensor on the distribitor so will find out if it was one of those this afternoon when i head to work

TPS tested fine on my volt meter so its down to the fuel pump now if it still does it lol

vadergator

two other things i didn't see anybody mention that could also be culprits. one, your IAC ( idle air control ) can cause problems going up steep hills when it's dirty / clogged / or going out. when mine started going bad, that was the first symptom to show up. later, i started having stalling issues and low rpms. second thing might be a stretch, but, check your speed sensor also. there's quite a few symptoms listed for it. the one that stands out to me is a sudden loss of power. might not be either one. the uphill struggles of your motor is what caught my eye and reminded me of my IAC experience. no codes or engine lights either with the problem. hope this helps.

bryzuky

yea the IAC has been on the back of my mind also that could be causeing it , luckly i have another one from my parts rig i took the motor out for my driver ( had to use the old motor throttle body due to newer motor being a 97 and my old one was really dirty and i cleaned it up some when i installed the motor but it was really nasty before and possable it is nasty again so going to swap it out this morning and try it sence its really easy to get to it cant hurt to try

zjrog

Fuel pump won't throw any specific code. It did throw codes that led me to change the O2 sensor, MAP sensor. I had changed the CPS earlier. But the ZJ had given me indications the pump was going, I had ripped the cat out thinking it was clogged, nope. Final straw was when my daughter and some friends were taking it for a trip and they didn't make it. They stopped for the night and the thing was just fine the next day.

Skid plate and receiver hitch makes dropping the tank a bit tougher if you are by yourself...