[xj_kid]

The stepper motor is on the left, just to the right there is another thing plugged into the TB, what is it? I replaced my stepper moter with a new one and it didn't solve anything.

1990 XJ Laredo 4.0 5spd 180kms

 

[316]

did you clean the seat that the stepper seals on?
Also I just noticed that yours is an older model and a diffrent system than either of my jeeps but the priciple Should be the same ,if the seat is not clean it will tend to stall when the gas pedal is released quickly!


91 jeep cherokee 270000 kms deceased
93 jeep grand cherokee living 213000 kms With
92 cherokee T case drop in!

 

[Andytron]

Jeff, you do have an EGR valve. Or more correctly you are supposed to.

 

[Guest]

Well than what is it, what does it do and where is it?

Jeff

86 XJ 2dr 2.8L auto 140kmi

 

[WilliamA]

My thoughts:
Do throttle position sensors (TPS) wear out? That is the other part on the TB. It electrically measures the position of the throttle plates (via voltage) so that the computer knows what rpm the engine is running at so it can compensate for timimg, emissions, and everything else it monitors. I forget whether or not this is actually open in the TB or not. If it is, maybe some carbon got on it when you were cleaing the TB. Or maybe, this part is not bad but just getting "lazy" from age and wear.
I think there will always be some sort of hesitation as the computer (brain) must "see" the position of the throttle and then compensate for that with increased timing and everything else. Kinda like touching something hot; a signal is sent to the brain, the brain analysis this information, then sends a response to the hand to let go. If this was immediate, we would never get a burn or blister.
I forget what the MAP (manifold absolute pressure) sensor controls but that may be something to look into. I'm not sure where yours is mounted (usually on the firewall) but it has a vaccum line going to it.
At my local Pep Boys, they have a diagram of all the components that make up the fuel injection system. The diagram shows stuff like "if you have this problem, this is the part to look at". Good luck!

Imagine life with no paved roadways!
Billy

 

[WilliamA]

Jeff
I have an 85 cherokee with the 2.8 liter engine and if you haven't changed that fuel filter in awhile, I think you will find a noticeable difference in acceleration. I remember when I changed my fuel filter, it seemed like I had a lot more power.
The filters we have in our carbs are made of paper, and I think that after time the pores get clogged (and dirty).
I know its a pain to get to but you should probably change it every 12000 miles...its cheap enough!
I recommend removing the front valve cover hold down to give you some slack in the fuel line. This is the screw right behind the conglameration of steel lines on the driver side valve cover. I beleive an 8mm deep socket with extension is what you will need to remove it.
I have found it almost impossible to remove the fuel line from the carb without doing this.
How old is your carb? I bought my trucknew in 85 and in 93, I had to replace the carb. It is now 01, and I just had my carb rebuilt by a local carb guy. It runs better then it ever has!!
FYI - I also removed the electric grid plate from under the carb. The carb guy told me this plate isn't really neccessary (it warms the gas for better vaporization on initial startup) and you may have problems as these things sometimes melt down.
And yes, you do have an EGR valve on that vehicle, mushroom shaped object behind the carb.


Imagine life with no paved roadways!
Billy

 

[Andytron]

The EGR(exhaust gas recirculation) valve does just that. At higher RPM's it opens slightly allowing some of the exhaust gas to be reburned by passing through the intake again. I'ts an emissions device. If the EGR valve is bad more than likely it is causing a vacuum leak through it's ruptured diapharm(sp?) and making your engine run crapier.

 

[Guest]

So it is like a turbo kit. But not as good. It uses the exhaust fumes as fuel making the engine more efficient and adding extra horsepower?

Jeff

86 XJ 2dr 2.8L auto 140kmi

 

[xj_kid]

Not quite, the best way to describe a turbo is forced induction. Air entering the engine first passes through an exhaust driven compressor. Compressed air results in a larger quantity of air being forced into the engine, creating more power.

The energy used to drive the turbo compressor is extracted from waste exhaust gasses. As exhaust gasses leave the engine they are directed through a wheel placed in the exhaust flow. The gasses drive the turbine wheel around, which is directly connected via a shaft, to the compressor wheel.

Increased exhaust gas drives the turbine wheel faster, this provides the engine more air, producing more power. A limit is met once a pre-determined boost pressure is achieved. At this point the exhaust gas is redirected away from the turbine wheel, thus slowing it down and limiting the maximum boost pressure. This redirection valve is known as the wastegate.

1990 XJ Laredo 4.0 5spd 180kms

 

[Guest]

I was by Advance Auto Parts ( old Western Auto ) and I saw a vacume pump there for around $15. It may be worth it to check each vac line one at a time to see if it leaks down. Cliff

'87 XJ 4.0, auto, 4-door
Hesco air tube, GDI three core, Borla header,
MSD Offroad w/8mm wires, 31-9.50 BS Duelers AT
headlamps on relays, Hella 550s,

 

[Guest]

Vaccum leaks can cause hesitation problems. A quick way to look for them is buy a can of CRC Brakekleen, green can, not the red since its non-flamable, some carb cleaners will work too) and with the engine idleing, spray around your vaccum lines, intake manifold gaskets and TB gaskets. Any leak will show up as there will be a temporary jump or decrease in the idle rpm.

 

[109]

WilliamA Welcome aboard!!...it is nice to see somebody with a 2.8 XJ that is an original owner besides my self....I've got an 86. /wwwthreads_images/icons/smile.gif

My 86 2.8 doesn't have that plastic grid under the carb. Instead, it has a exhaust manifold stovepipe to help vaporize the fuel in cold conditions. Do you have the "big journal" 2.8? They introduced the big journal engines in mid 1985.

For all:

The function of the EGR valve is to reduce the combustion chamber temperatures. It can reduce them by hundreds of degrees! Since modern engines have to have a cat convertor, the exhaust temp is critical and the engines need to run leaner for the cat to work effectively and not be destroyed. Trouble is lean running engines combustion temps can be so high that they will actually burn exhaust valves to a crisp and wreck the cat. So to reduce the combustion temps, the EGR was used to put a bit of inert exhaust in the cylinder to keep the temps down. The exhaust gas doesn't burn and that cools the reaction in the cylinder. The small amount of EGR gas doesn't noticeably affect the power and torque the engine produces. Some prefer to disconnect the EGR but given the consequences, burned exhaust valves and destroyed cat, I wouldn't recommend it./wwwthreads_images/icons/crazy.gif/wwwthreads_images/icons/smile.gif

 

[Andytron]

Jim you hit the nail on the head. I don't need to explain any further. You get all that Jeff?

 

[Guest]

Yup I got it. Thanks.

Jeff

86 XJ 2dr 2.8L auto 140kmi

 

[109]

So, no, Jeff, the EGR is not like a turbocharger..in a turbo, the exhaust gas and intake air never mix.

 

[WilliamA]

Thanks pooh bah!
I too have the stove pipe coming up from the header. Maybe that grid thing serves some other purpose. But I now have no abstructions for the incoming aircharge.
I'm not sure if I have the "big journel" or not. All I can tell you about internally is that the heads have the "vains" on the intake port. I noticed this when I had to replace the leaky intake gasket that allowed antifreeze to seep into the oil. Not good!
It's amazing what this carb rebuild has done as far as performance goes. WOW! Not that I am tearing up the street but what a difference.
Everyone badmouths this engine but ya know, it's been a VERY RELIABLE engine/vehicle.

Imagine life with no paved roadways!
Billy

 

[109]

I thought that grid was an electric heater to warm the fuel/air mix during cold running after start up. My 1986 XJ 2.8 didn't have one but my nephew's 1982 Camaro 2.8 does.....

Glad you are happy with your rebuild......Tim "the Sandman" has a Holley rebuilt Rochester 2SE on his S-15's 2.8.....he is pleased with his also. My never touched, except for cleaning with carb cleaner spray, 2SE is doing well...I'm getting about 15 MPG city and 20 highway. My XJ has currently 133,000 miles on it./wwwthreads_images/icons/smile.gif

 

[WilliamA]

Funny??
I replaced my original carb back in 93. I started to notice that when I accelerated, the engine would bog and sputter. Finally, on the way to work it just died as I was driving it.
Bought a rebuild for $325 and that ran fine up to about a year ago. The main problem was that the choke stopped working. I had to put an umbrella against the pedal to keep the rpms up so the engine would warm in the morning. And if the engine wasn't fully warmed, the Jeep would buck (and sometimes stall) while trying to accelerate.
The rebuild cost me $185. This was money definitely well spent!
I have 124,000 on my engine/vehicle.

Imagine life with no paved roadways!
Billy

 

[2423]

ok i have no clue where the other post on hestitation went so i'm bringin this one back from the past..........

heres what happens to mine...

i have hesitation during parking lot driving and if i have my foot completely still on the petal, not accelerating, just trying to go at a set speed... my jeep will buck and drop rpms.... the engine seems to be having alittle trouble getting power... now this only happens when i'm goin like under 45 mph

 

[2336]

I just had the same problem after I replaced my temp.sending unit. At some time during the install I cracked the vaccum line that goes to the MAP sensor. Fixed the line works great.

Jody