Jeep keeps bogging. I need help - JeepForum.com
 
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post #1 of 12 Old 10-21-2019, 06:32 PM Thread Starter
Atticus_6147
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Jeep keeps bogging. I need help

Last week my jeep started to hesitate while accelerating. It was like it was being limited on power. And one thing I've learn about our 4.0's is there is no limit to its power.

So when I'm back at the house I check for codes and it gave me code 23 for the tps. No problem. Bought a new tps. Same symptoms as before. So I grab my pressure gauges. Pressure at the rail is low so I swap in a new fuel pressure regulator. No change. Must be the fuel pump. Swap in a new one no change. Find out the o ring tore on the fuel pressure regulator during first install, replaced and perfect pressure.

Now she hold 31psi and holds it for a while after shut off. I use a volt meter on the tps and it is in specs. Iac and throttle body are clean. No vacuum leaks that I can see. Pulled the rail and turn the key to on and no leaky injectors. Thought it was my cat so I drilled a small hole but no change.

The problem. She will start and idle just fine. But when you press the gas, you hear air sucking and it bogs down and wants to die.

What am I missing?

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post #2 of 12 Old 10-21-2019, 07:49 PM
Bigskyj
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I would start by checking for vacuum leaks. Check the vacuum ball things to make sure they aren't cracked or broke. Check the brake booster for leaks. Check intake manifold bolts etc. I like to use a little propane torch to search for vacuum leaks by directing propane directly where i suspect a leak. If the idle changes that area has become my first suspect.
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post #3 of 12 Old 10-22-2019, 04:27 AM
jtec
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what is the voltages at the TPS?
Violet wire?
Orange wire?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 12 Old 10-22-2019, 07:19 AM Thread Starter
Atticus_6147
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I just tested the middle wire. I can't remember which color it is right now. But it was at .79 and at wot it is at 3.46.
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post #5 of 12 Old 10-22-2019, 05:41 PM
88YJtoCJ
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Quote:
Originally Posted by Bigskyj View Post
I like to use a little propane torch to search for vacuum leaks by directing propane directly where i suspect a leak. If the idle changes that area has become my first suspect.



X2 on this.


I also take a little propane torch, just turn the gas on and start waving around different areas (especially the ends of the intake manifold). I found I had a gap from a bolt that shook loose on my intake manifold closest to the firewall. It was large enough for me to fit the straw from my carb cleaner bottle. The Bolt had shaken loose and fallen out completely from the bottom.



Funny enough it would still run, Idle like crap, misfiring but would completely bog down when getting on the throttle by any margin.


Since you hear air, its most likely a vacuum leak somewhere.

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post #6 of 12 Old 10-22-2019, 06:41 PM
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Where is the air sucking noise coming from? A really lean carb or TBI system sound like they are sucking air when they are bogging through the throat of the TBI or carb.

TBI systems often have the symptom of a high idle when they have a vacuum leak.

I agree with checking for vacuum leaks but by your description it does not sound like it is your issue. Your TPS voltage is low at WOT but that could be your throttle cable or brackets etc. not allowing full throttle from the pedal. An adjustment or travel issue.

Drilling a small hole in a cat matters on location of the hole. Not a way I would ever relieve exhaust pressure by any means. A small enough hole that is not intrusive which is what it sounds like you did is not going to alleviate the symptoms of a plugged cat anyways. Either remove the 02 before the cat and drive it quickly or disconnect exhaust upstream of cat and do same. Pay attention though because hot exhaust gasses are escaping in bad places. Can cause other unwanted combustion.... IE a fire or melting of something bad. A plugged cat to me has a distinct sound that I would not call sucking air but could be interpreted as that by somebody not familiar with the sound. Cats can also be diagnosed by doing exhaust back pressure testing which can be done with a fitting in the 02 hole for example and a pressure gauge. Most pressure gauges cannot do this for a long period of time because there is too much heat put into them.

Does your TPS code return after replacing the sensor?

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #7 of 12 Old 10-23-2019, 08:22 AM Thread Starter
Atticus_6147
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Hey

The tos code does return. Is there a way to adjust my cable so my wot reads higher?

Also, I'm with y'all that I may have a vacuum leak causing my issues. Are there any secrets to tracking them down?
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post #8 of 12 Old 10-23-2019, 08:37 AM
88YJtoCJ
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Quote:
Originally Posted by Atticus_6147 View Post
Hey

Also, I'm with y'all that I may have a vacuum leak causing my issues. Are there any secrets to tracking them down?



Wave around an unlit propane torch, or spray carb/intake cleaner randomly around your manifold, by the brake booster connection (try not to spray chemicals on hoses themselves).


The vacuum leak will suck in the propane or the carb cleaner, which is flammable, which will end up in a cylinder and combust, increasing your engine RPMs, so if you find a spot you can spray near and your RPMS increase you found a vacuum leak.


If you have extra flexible fuel line or similar, you can also put one end near your ear and use the other end pointed at different areas to listen for the hiss/sucking vacuum.



If it is a vacuum leak, by far the easiest method I have used is the unlit propane torch bottle, the carb cleaner if you spray it too close to the actual leak and get more liquid than atomized spray can stall the engine or lower RPM rather than raise the RPM. Propane is guaranteed to increase the RPM. Turn the gas on and pretend like your are running a flame (but your not, its UNLIT!) along your intake manifold gasket, blow some propane fumes at and around your brake booster. Keep it pointed away from your air filter, as it will suck in the fumes and raise RPM as it travels through the throat of your

intake.


Also a common missed spot are EGR Valves, when those start leaking they are often times missed for quite some time. Any Vacuum accessory, either on ported or manifold vacuum could be the culprit.


If you can't seem to find anything to make RPM's increase, then vacuum isn't your issue. Beyond mechanical / vacuum reasons my knowledge stops, I have no sensors in my 88.

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post #9 of 12 Old 10-23-2019, 08:58 AM
jtec
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for vacuum leaks - use the old school carb spray technique,

As far as TPS voltage we need the referance voltage - if its low you will have a skewed output.

3.5V SEAMED low FOR REFERANCE @5V IS EXPECTED.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 12 Old 10-23-2019, 06:37 PM
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Quote:
Originally Posted by jtec View Post
for vacuum leaks - use the old school carb spray technique,

As far as TPS voltage we need the referance voltage - if its low you will have a skewed output.

3.5V SEAMED low FOR REFERANCE @5V IS EXPECTED.
Damn good point. Need to verify both reference and ground. VERY GOOD POINT!!!

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #11 of 12 Old 10-23-2019, 06:47 PM
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Quote:
If it is a vacuum leak, by far the easiest method I have used is the unlit propane torch bottle, the carb cleaner if you spray it too close to the actual leak and get more liquid than atomized spray can stall the engine or lower RPM rather than raise the RPM.
This does not actually matter. If the RPM's raise or lower it indicates a significant vacuum leak or a combustible being introduced from a place where it is not supposed to be introduced from.

Quote:
Also a common missed spot are EGR Valves, when those start leaking they are often times missed for quite some time. Any Vacuum accessory, either on ported or manifold vacuum could be the culprit.
This is an awesome point. It brings to mind that some EGR valves were also called positive or negative backpressure valves in that era. I cannot say for sure if these EGR valve were either but a slightly restricted exhaust or even internal EGR port that monitored said pressure could be the culprit. Some issues can be caused by an EGR "tipping in" to quickly. In laymans terms this means the EGR opens too quickly. The EGR does not necessarily have a leak, it just opens up too fast.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #12 of 12 Old 10-23-2019, 10:21 PM Thread Starter
Atticus_6147
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My jeep is a 93 so I don't believe it has an egr valve. I'll give the propane gas a try tomorrow. Thanks for the input.
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