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Hard starting/hesitation on accel

Cottontail

Cottontail

Three-De Off-Road
Location
Nashville, TN
In my 1990 from cold, I need to hit the gas and hold the key over several seconds in order for it to catch. It still doesn't catch immediately when it is warm either.

Then, when it starts it revs to about 2500 rpm before dropping back down to about 500/600.

FYI...plugs and wires, battery and cables, distributor are all new and the igintion timing is dead on.

Could it be as simple as needing a new starter? I am not certain how old the starter is, but the truck had 169xxx on it and the starter has about 1/4 inch of grease and oil on it.

Also, occasionally I will get some stumbling/hesitation when accelerating. Sometimes it is from a stop, sometimes at 20-25 miles an hour, sometime going from 60-65 mph. There is no real constant. It seems to hesitate anytime it feels like it!

I have swapped out my IAC and it helped some, but not a lot. I am still in my first full tank of fuel since we got it running, so I am trying to get 20 gallons of "good" gas through the engine to clean things up.

Someone mentioned the throttle control switch should be set at about 14 degrees or 14%, I can't recall. How do I find out if it is at 14 degrees/14%?

Thanks y'all.
 
Cottontail said:
In my 1990 from cold, I need to hit the gas and hold the key over several seconds in order for it to catch. It still doesn't catch immediately when it is warm either.

Then, when it starts it revs to about 2500 rpm before dropping back down to about 500/600.

FYI...plugs and wires, battery and cables, distributor are all new and the igintion timing is dead on.

Could it be as simple as needing a new starter? I am not certain how old the starter is, but the truck had 169xxx on it and the starter has about 1/4 inch of grease and oil on it.

Also, occasionally I will get some stumbling/hesitation when accelerating. Sometimes it is from a stop, sometimes at 20-25 miles an hour, sometime going from 60-65 mph. There is no real constant. It seems to hesitate anytime it feels like it!

I have swapped out my IAC and it helped some, but not a lot. I am still in my first full tank of fuel since we got it running, so I am trying to get 20 gallons of "good" gas through the engine to clean things up.

Someone mentioned the throttle control switch should be set at about 14 degrees or 14%, I can't recall. How do I find out if it is at 14 degrees/14%?

Thanks y'all.
Click to expand...

Maybe also a TPS? Run a bottle of Lucas Fuel Injector Cleaner as well. Does not sound like a starter though.
 
When I said throttle control switch, I meant throttle position sensor. That is what I talked about with the 14% or 14 degrees. There are too many acronym parts under the hood!!!

As far as the fuel injectors, they are brand new, with less than 100 miles on them, so I am not sure Lucas will do any good...

Thanks for the ideas though.

Anyone else???
 
Cottontail said:
When I said throttle control switch, I meant throttle position sensor. That is what I talked about with the 14% or 14 degrees. There are too many acronym parts under the hood!!!

As far as the fuel injectors, they are brand new, with less than 100 miles on them, so I am not sure Lucas will do any good...

Thanks for the ideas though.

Anyone else???
Click to expand...

OK, then try your TPS. Also they cannot be "set" they come in a certain place, and that's about it. It's a $28 part, and maybe 5min to install using a T-15 bit. I would start there, I had similar problems in a ZJ I had a few years back, the TPS solved everything. They can be tested though, by back probing the connector and seeing if it is sending the correct reading to the ECU.

OPERATION

See Figure 1

The throttle position sensor is mounted on the throttle plate assembly and provides the ECU with an input signal of up to 5 volts to indicate throttle position. At minimum throttle opening (idle speed), a signal input of approximately 1 volt is transmitted to the ECU. As the throttle opening increases, voltage increases to a maximum of approximately 5 volts at the wide open throttle position.

A dual TPS is used on models equipped with automatic transmission. This dual TPS not only provides the ECU with input voltages, but also supplies the Transmission Control Unit (TCU) with an input of throttle position.


Fig. 1: Throttle position switch (A) used on vehicles with manual transmissions and (B) used on vehicles with automatic transmissions



TESTING

  1. Unplug the connector at the TPS.
  2. Check the voltage between the black and grey wires with the key ON. Voltage should be approximately 5 volts. If the proper voltage is not present, check the harness for shorts or opens.
  3. Engage the wire connector to the TPS. With the key ON, and the throttle plate closed, check the voltage between the blue and the black wires. Voltage should be approximately 0.8 volts.
  4. If voltage is not correct, loosen the screws securing the TPS and adjust until 0.8 volts is present.
  5. If adjusting does not bring sensor voltage to specification, replace the TPS.

Good luck,

Todd
 
Last edited:
mine is doing the same thing and is the same year model but with the 5 speed and inline 6 i went to check it and there is a blue and brown wire but not what you listed are those the correct wires to look at??
 
Have some one test your fuel pressure. I had the same problem hard start and no power / hesitation. It turned out to be the fuel pump. I took the pump out and the internal fuel hose slipped off causing the fuel pump to suck air and lose pressure in the system. I hope this helps. Keep us posted on what you find out.

Chad
 
i went and bought a new tps yesterday and installed it today.. but the thing is terrible..... when i start the truck the rpm goes sky high and just stays there I adjusted the tps and there is no change if i unplug the tps the idle drops back down then when i plug it back in it idles normal until i shut it off and turn is back on..... what the heck is that about??????
 
I have this same issue on my 89 4.0, and it just started recently. I have to hit the gas when it is cold to get it started. Sometimes it will die as I hit the gas to get going, but only once, and right after it has sat all night. I can drive around the rest of the day with many stops, and not have another starting or hesitation issue. I haven't had time to mess with it yet, but I will let you know if I find anything out.
 
keg0900 said:
i went and bought a new tps yesterday and installed it today.. but the thing is terrible..... when i start the truck the rpm goes sky high and just stays there I adjusted the tps and there is no change if i unplug the tps the idle drops back down then when i plug it back in it idles normal until i shut it off and turn is back on..... what the heck is that about??????
Click to expand...

I'm pretty sure that means you got a faulty TPS.
 
Mine acted up again this morning, but I also noticed a puff of white steam/smoke when it failed to start. I saw it rise from the driver's side in the front. When mine behaves like this, I sometimes get a high-pitched farting noise from the engine compartment. (not sure of a better way to describe it) This only happens for less than a second. That is what I heard just before the steam/smoke rose. This was a cold engine that had been sitting all night. I am thinking this has to be pressure escaping through the induction system, but I am still not sure what is going on. This happen to any of you guys? BTW, I got it started, and everything ran fine.
 
Mine is doing the same thing.

Ok, here I am yet again.

Well I have yet another problem with my '91 Cherokee Briarwood. Now for some strange reason my rig won't start. There is no juice going to anything inside the rig. Any ideas of what could be causing this

The only thing that works is the brake lights when you step on them, and my emergency lights

And my buddy has this too add

My guess is it's a piece... oh wait. lol
We've looked at this thing & I just can't figure it out (but electrical is by far not my expertiese). Here's the situation:

First, he had a short somewhere that caused the rear hatch wiring to short on the right hand side where the harness plugs into the rest of the hatch. Looked to be part of the defrost and wiper motor. I figured it was due to the crappy wiring of the speakers that someone else had done, so I got a new harness for him and plugged it all up. Most everything was working after that. On his way home, apparently it did the same thing, and this time fried (literally) his fuse box. The park lamp fuse is literally melted, so no brake lights except when actually hitting the brakes, no park lamps, no wiper, no speakers, no defrost, and no guage lights (not sure how that was connected, but it was). However, the Jeep still ran & started.

We went to Slaughterhouse on the 2nd, everything went fine, made a few stops on the way back, and ended up at my place to look at the pics from the day. On his way out, wouldn't start. Battery is fine, even tried jumping it & nothing. No juice anywhere, but as Blaze said, the flashers and brake lights will still work. No headlights, horn, interior lights, locks, windows, etc- nothing (as if there were no battery). All the fuses seemed to be inline (with the obvious exception of the melted ones). He has a wierd security feature on the Jeep which I think might be cutitng power, but I can't even get power on to test the theory. Any ideas?
 
DKBlaze said:
Mine is doing the same thing.

Ok, here I am yet again.

Well I have yet another problem with my '91 Cherokee Briarwood. Now for some strange reason my rig won't start. There is no juice going to anything inside the rig. Any ideas of what could be causing this

The only thing that works is the brake lights when you step on them, and my emergency lights

And my buddy has this too add

My guess is it's a piece... oh wait. lol
We've looked at this thing & I just can't figure it out (but electrical is by far not my expertiese). Here's the situation:

First, he had a short somewhere that caused the rear hatch wiring to short on the right hand side where the harness plugs into the rest of the hatch. Looked to be part of the defrost and wiper motor. I figured it was due to the crappy wiring of the speakers that someone else had done, so I got a new harness for him and plugged it all up. Most everything was working after that. On his way home, apparently it did the same thing, and this time fried (literally) his fuse box. The park lamp fuse is literally melted, so no brake lights except when actually hitting the brakes, no park lamps, no wiper, no speakers, no defrost, and no guage lights (not sure how that was connected, but it was). However, the Jeep still ran & started.

We went to Slaughterhouse on the 2nd, everything went fine, made a few stops on the way back, and ended up at my place to look at the pics from the day. On his way out, wouldn't start. Battery is fine, even tried jumping it & nothing. No juice anywhere, but as Blaze said, the flashers and brake lights will still work. No headlights, horn, interior lights, locks, windows, etc- nothing (as if there were no battery). All the fuses seemed to be inline (with the obvious exception of the melted ones). He has a wierd security feature on the Jeep which I think might be cutitng power, but I can't even get power on to test the theory. Any ideas?
Click to expand...


This sounds like a serious electrical issue, but this is a different issue than the one in this thread. How are your ground wires looking? Take a look at your ignition switch, too. That could be fried. It is on top of the steering column.
 
I had another issue this weekend which makes me think the TPS is the culprit. I started it up after a cold night, with the aforementioned starting symptoms, and I put it in gear(AW4) and took off. The tranny would not shift out of first for a few blocks. It did this twice. Only when cold, and after a few blocks, the trans was behaving normally. Anyone care to chime in?
 
when replacing the TPS, how do you know where to set it? so it's in the right position? I have replaced the 1 on my V8 Fiero, but i have an aftermarket fuel managment system and the programmer for it. I have nothing in the way of comp equipment for my 89 XJ (it's a 4L/AW4 as well)

thanks
 
Rather than going thru a lengthy process here, try doing a search for TPS adjustment. Every Renix that I know of takes a few secs. to start, don't know if thats what you have.
As for the TPS mine started doing the "a gizillion RPM's" after start thing too. Checked the TPS and it was out of adj, luckily I could get back in limits and this worked until it went altogether. Mine is an AW4 so it it was more evpensive, somewhere around $70 from NAPA. Replaced, adjusted and all is well.
 
as it turned out my TPS was waaaaay out of adjustment, i found a great link on how to check and set it properly. now it purrs like a kitten, no more rough idle and not a hint of hesitation
 
Glad to hear you fixed it. party1:

I still need to do this, but I have to get a DMM. I think my foot has been trained to feather the gas while I start it.
 
colin said:
as it turned out my TPS was waaaaay out of adjustment, i found a great link on how to check and set it properly. now it purrs like a kitten, no more rough idle and not a hint of hesitation
Click to expand...

Hi - could you send me the link to the article you read on adjusting a Renix XJ's TPS??

Thanks,
Ted
 
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