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Unread 02-08-2010, 07:49 PM   #61
yellowoctupus
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Fair enough laybackman, I'll toss a light on it. Thanks for the heads up on starting a new thread. It's certainly not 180 off in this case, as once it fires it runs like a charm, but it certainly may be off some amount.

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Unread 02-08-2010, 08:56 PM   #62
laybackman
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Originally Posted by yellowoctupus View Post
Fair enough laybackman, I'll toss a light on it. Thanks for the heads up on starting a new thread. It's certainly not 180 off in this case, as once it fires it runs like a charm, but it certainly may be off some amount.
I wasn't busting your chops about placing your question in an old post. It's just that you may not get any response from any one because of the age of the post.

I think the timing light will tell you what may be off in your engine.
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Unread 09-27-2010, 07:36 AM   #63
CJHVN
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Didn't want to dig up an old thread, but I'm having the same issues. Quick background...1985 Jeep CJ-7 with a 1994 Wrangler 4.0L. Engine is in mechanically and wired up correctly. All sensors have been changed to new, all wiring is complete and working, fuel pump is working and have perfect pressure at the rail, all injectors are firing and read perfectly on the ohm test, but I have a weird hesitation when I hit the gas. It idles perfectly, runs great with throttle, but there is a short hesitation when I FIRST give it gas. Any ideas?

Also, I got the engine to TDC, set the distributor, it's running great, but with a timing light, it's running at about 12-14 degrees after 0. Out of curiosity, I just checked my stock Cherokee with the same engine and it's almost exactly the same. Why wouldn't they both be at running at 0? Am I missing something here?

Any help would be great.
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85 CJ-7, 4.0L, twin stick/clocked flat Dana 300, SOA, 36" TSL's, 30/44 locked, Warn X8000i

92 XJ, 4.0L, AW4, Dropped NP231, 30/8.25, 4" DPG Hybrid lift, 33" MT/R's, JKS trackbar, JKS discos, OME Nitro Shocks, stinger bumper, Warn X8000i, etc. (work in progress)
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Unread 09-27-2010, 10:47 AM   #64
laybackman
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Originally Posted by CJHVN View Post
Didn't want to dig up an old thread, but I'm having the same issues. Quick background...1985 Jeep CJ-7 with a 1994 Wrangler 4.0L. Engine is in mechanically and wired up correctly. All sensors have been changed to new, all wiring is complete and working, fuel pump is working and have perfect pressure at the rail, all injectors are firing and read perfectly on the ohm test, but I have a weird hesitation when I hit the gas. It idles perfectly, runs great with throttle, but there is a short hesitation when I FIRST give it gas. Any ideas?

Also, I got the engine to TDC, set the distributor, it's running great, but with a timing light, it's running at about 12-14 degrees after 0. Out of curiosity, I just checked my stock Cherokee with the same engine and it's almost exactly the same. Why wouldn't they both be at running at 0? Am I missing something here?

Any help would be great.
Timing is controlled by the brain. If the distributer is in right no adjustments are possible. Basically, the crank and cam position sensors tell the brain what is where and when to fire or shoot fuel into which cylinder. The throttle position sensor tells the brain how deep you have mashed your skinny pedal.

No matter where it is the timing will get corrected IIRC, BUT your fuel delivery would be off. If the sensors are sending back information then the hesitation could be related to the Throttle Position Sensor (TPS). If it is mounted on a loose/worn throttle shaft that could be your problem.
Keep in mind that you will not get instant response from an engine whose design is basically over forty years old and your mechanical parts are not new either.
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Unread 09-27-2010, 12:24 PM   #65
CJHVN
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I understand that the timing is controlled by the ECM. I'm positive that the distributor is installed correctly. I used the procedure listed in the factory service manual for this year/make engine.

I guess my question has two parts:

1. Why does the timing light indicate that the timing is running near 12-14? I thought this was strange so I checked my bone stock Cherokee with the same engine and it's running exactly the same. Is that normal? Is the ECM adjusting the idle on both engines for some reason?

2. Wouldn't a faulty TPS cause problems anywhere in the throttle? It's ONLY hesitating when I first hit the gas, then it smooths out throughout the entire throttle range. The hesitation is very minor. It's just a little "cough" when you first hit the throttle, then it's fine. It's made worse if I bump the throttle fast and hard.
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85 CJ-7, 4.0L, twin stick/clocked flat Dana 300, SOA, 36" TSL's, 30/44 locked, Warn X8000i

92 XJ, 4.0L, AW4, Dropped NP231, 30/8.25, 4" DPG Hybrid lift, 33" MT/R's, JKS trackbar, JKS discos, OME Nitro Shocks, stinger bumper, Warn X8000i, etc. (work in progress)
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Unread 09-27-2010, 02:57 PM   #66
laybackman
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Quote:
Originally Posted by CJHVN View Post
I understand that the timing is controlled by the ECM. I'm positive that the distributor is installed correctly. I used the procedure listed in the factory service manual for this year/make engine.

I guess my question has two parts:

1. Why does the timing light indicate that the timing is running near 12-14? I thought this was strange so I checked my bone stock Cherokee with the same engine and it's running exactly the same. Is that normal? Is the ECM adjusting the idle on both engines for some reason?

2. Wouldn't a faulty TPS cause problems anywhere in the throttle? It's ONLY hesitating when I first hit the gas, then it smooths out throughout the entire throttle range. The hesitation is very minor. It's just a little "cough" when you first hit the throttle, then it's fine. It's made worse if I bump the throttle fast and hard.
Check the throttle shaft that the TPS is attached to see if there is any play in it. It may just be an age related issue. You will not get as fast a throttle response or you might get a minor 'stumble' when you pop the skinny pedal out of an early 90's 4.0 as opposed to a rice burner with MPFI and OBDll electronics. A 94 motor and accessories is 17 model years old.
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Getting older, I have developed some special skills. I have the ability to cough, sneeze, fart and pee at the same time.

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Unread 09-27-2010, 04:14 PM   #67
CJHVN
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I realize this thing is 17 years old and the technology was limited back then.

This is a completely rebuilt engine with all new accessories and sensors. No matter how old the technology is, it still should hesitate when you hit the throttle. It coughs and sputters before it revs up. That shouldn't happen no matter how old it is unless there is an issue of some kind.

I guess that's what I'm trying to figure out. Thanks for your help.
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92 XJ, 4.0L, AW4, Dropped NP231, 30/8.25, 4" DPG Hybrid lift, 33" MT/R's, JKS trackbar, JKS discos, OME Nitro Shocks, stinger bumper, Warn X8000i, etc. (work in progress)
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Unread 09-27-2010, 04:41 PM   #68
Curly5759
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Quote:
Originally Posted by CJHVN View Post
I understand that the timing is controlled by the ECM. I'm positive that the distributor is installed correctly. I used the procedure listed in the factory service manual for this year/make engine.

I guess my question has two parts:

1. Why does the timing light indicate that the timing is running near 12-14? I thought this was strange so I checked my bone stock Cherokee with the same engine and it's running exactly the same. Is that normal? Is the ECM adjusting the idle on both engines for some reason?

2. Wouldn't a faulty TPS cause problems anywhere in the throttle? It's ONLY hesitating when I first hit the gas, then it smooths out throughout the entire throttle range. The hesitation is very minor. It's just a little "cough" when you first hit the throttle, then it's fine. It's made worse if I bump the throttle fast and hard.
1) Your timing is normal.
2) TP sensors are a 'sweep' type variable resistor. The sweep part of the sensor rubs against a resistor. As the throttle opens, the sweep moves along the resistor changing the voltage going to the pcm. Since the sweep must move from idle every time you accelerate, that part of the sensor wears first.
This causes a hesitation in the acceleration of the engine, since the voltage the pcm sees does not relate to the actual amount of air entering, so injection is not correct. (engine goes lean momentarily)

Those of us old enough to remember carburetors knew when this happened, we needed an accelerator pump. The tps is alot like an electronic accelerator pump.

curly
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Unread 09-27-2010, 05:00 PM   #69
laybackman
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Quote:
Originally Posted by CJHVN View Post
I realize this thing is 17 years old and the technology was limited back then.

This is a completely rebuilt engine with all new accessories and sensors. No matter how old the technology is, it still should hesitate when you hit the throttle. It coughs and sputters before it revs up. That shouldn't happen no matter how old it is unless there is an issue of some kind.

I guess that's what I'm trying to figure out. Thanks for your help.
Less older parts means less possibilities for problems. I would sttill look at the maain shaft on tthe TB which the TPS is attached to. If there is any wwar in that shgaft it just might be in the TPS. Or....it is up in the distributer. It is not advacning *** fast as it should and your engine 'bogs' until the timing gets to where it belongs.
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Getting older, I have developed some special skills. I have the ability to cough, sneeze, fart and pee at the same time.

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Unread 09-27-2010, 05:29 PM   #70
CJHVN
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Quote:
Originally Posted by Curly5759 View Post
1) Your timing is normal.
2) TP sensors are a 'sweep' type variable resistor. The sweep part of the sensor rubs against a resistor. As the throttle opens, the sweep moves along the resistor changing the voltage going to the pcm. Since the sweep must move from idle every time you accelerate, that part of the sensor wears first.
This causes a hesitation in the acceleration of the engine, since the voltage the pcm sees does not relate to the actual amount of air entering, so injection is not correct. (engine goes lean momentarily)

Those of us old enough to remember carburetors knew when this happened, we needed an accelerator pump. The tps is alot like an electronic accelerator pump.

curly
1. Why does the timing read so high at idle? Shouldn't it read closer to 0?

2. That makes senses to me. But, if I recall the TPS on mine is fairly new, but that's not saying there isn't an issue with it. I'll replace it and see if the problem goes away.

Thanks for the help. Good answers guys.
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92 XJ, 4.0L, AW4, Dropped NP231, 30/8.25, 4" DPG Hybrid lift, 33" MT/R's, JKS trackbar, JKS discos, OME Nitro Shocks, stinger bumper, Warn X8000i, etc. (work in progress)
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Unread 09-27-2010, 05:33 PM   #71
CJHVN
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Wow! Just went out and looked under the hood. My buddy installed the distributor and the #1 post is at the 1 o'clock position if you're looking at the engine from the passenger side.....maybe that's the problem....duh!

Working with friends is tough sometimes.....

I'll still change out the TPS though. I'm sure that must be what's causing that slight hesitation on throttle up from idle.
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85 CJ-7, 4.0L, twin stick/clocked flat Dana 300, SOA, 36" TSL's, 30/44 locked, Warn X8000i

92 XJ, 4.0L, AW4, Dropped NP231, 30/8.25, 4" DPG Hybrid lift, 33" MT/R's, JKS trackbar, JKS discos, OME Nitro Shocks, stinger bumper, Warn X8000i, etc. (work in progress)
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Unread 09-27-2010, 05:51 PM   #72
laybackman
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Quote:
Originally Posted by CJHVN View Post
Wow! Just went out and looked under the hood. My buddy installed the distributor and the #1 post is at the 1 o'clock position if you're looking at the engine from the passenger side.....maybe that's the problem....duh!

Working with friends is tough sometimes.....

I'll still change out the TPS though. I'm sure that must be what's causing that slight hesitation on throttle up from idle.
At mechanical TDC where is the rotor relative to the no1 post on the dist. tower? THAT is what is important.
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Getting older, I have developed some special skills. I have the ability to cough, sneeze, fart and pee at the same time.

"If we cannot afford to take care of Veterans, then we should stop making them."
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Unread 09-27-2010, 06:09 PM   #73
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Quote:
Originally Posted by CJHVN View Post
1. Why does the timing read so high at idle? Shouldn't it read closer to 0?
That is not an unusual number for ignition timing. Base timing on a lot of Fords is 10* BTDC and GM's at 12* BTDC
You have to remember the piston is really moving very fast in the cylinder, even at idle. If you fire the spark plug at "0", by the time the mixture ignites and creates pressure in the cylinder, the piston is already on its way down.
Firing the plug before "0", give the mixture more time to burn, creating more psi in the cylinder, more mpg and less emissions. This is why timing automatically advances as engine speed increases.


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Unread 09-27-2010, 07:54 PM   #74
CJHVN
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Good info. Thanks for the advice guys. I'm learning!

Keep it coming.....
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92 XJ, 4.0L, AW4, Dropped NP231, 30/8.25, 4" DPG Hybrid lift, 33" MT/R's, JKS trackbar, JKS discos, OME Nitro Shocks, stinger bumper, Warn X8000i, etc. (work in progress)
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Unread 09-27-2010, 07:55 PM   #75
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Quote:
Originally Posted by CJHVN View Post
Wow! Just went out and looked under the hood. My buddy installed the distributor and the #1 post is at the 1 o'clock position if you're looking at the engine from the passenger side.....maybe that's the problem....duh!

Working with friends is tough sometimes.....

I'll still change out the TPS though. I'm sure that must be what's causing that slight hesitation on throttle up from idle.
You can in fact set up the distributor to work properly in 6 different positions. Just make sure that you either know what you're doing if you don't like the "factory designated" position, or follow the factory service manual instructions that I posted very early in this thread.

From my "read" of your problem, it's not timing related. If you set up the distributor improperly with #1 at TDC, the engine either wouldn't start at all or it would start hard and run very poorly because the setup would be approximately 27 degrees retarded. As a quick guess, your hesitation is throttle body/sensor related. Have you checked the fuel pressures?

I recommend that you start a new thread, this one is way too long & you won't get too much attention - no one likes re-reading this much old history.
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