1999 Jeep Wrangler boging down when driving

Tiny
MIDATLANTIC1
  • MEMBER
  • 1999 JEEP WRANGLER
  • 4.0L
  • 6 CYL
  • 4WD
  • MANUAL
  • 122,000 MILES
Jeep 1999 wrangler

runs normal standing still when a load is placed on it it boggs down and dies until I let off the accelerator

changed the TPS and The Air intake control valve per computer
50lbs at the rail and steady fuel pressure
changed the filter in the fuel pump
just removed the catylitic converter today obviously can/t tell however,
i ran a hair dryer in the end and no back pressure and it seamed to be coming out as strong as it was going in
but I dont have another way of testing it also put on the muffler just in case and it seamed normal

there are no engine lights
have not checked the injectors for clogging
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Monday, March 30th, 2015 AT 2:00 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
If you're trying to measure back pressure in the exhaust system with a hair dryer, that will never work. Of course what comes out will be the same as what's going in. Where else is the air going to go? A running engine at idle is going to move a hundred times more air volume, and that's what has to be able to get through. The clue to a restricted catalytic converter is you'll tend to hear a steady hiss from the tail pipe instead of the normal "putt putt", and the engine will run hot with low power. If you suspect a restricted exhaust system, there's a tool made for measuring it. This requires drilling a small hole ahead of the converter, then sticking the tool's probe in there.

What led you to the throttle position sensor? That has almost no effect in fuel metering calculations and will not cause low power. Have you checked for diagnostic fault codes? Do you have access to a scanner to view live data from the Engine Computer?
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Monday, March 30th, 2015 AT 3:52 PM
Tiny
MIDATLANTIC1
  • MEMBER
I do not have access to live data the scan tool cost to much I had a obd2 that read a bad tps and aig so I replaced it. Sorry about the hair dryer its a hill billy afternoon I am not hearing hissing sound on the tail pipe and the car did not get to hot normal temp levels now I have removed the cat converter back to the manifold actually the bracket had rusted and needed to be replaced it was very loose at the manifold how about injectors? But my question is could one injector create such a loss in power its not sputtering all the cylinders seam to be firing it idles well

I have not checked wires but cleaned and set plugs to proper gap
rotter cleaned
have not check injectors for voltage or resistance
do I need a live scan? Any other suggestions
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Monday, March 30th, 2015 AT 4:10 PM
Tiny
CARADIODOC
  • EXPERT
The biggest mistake is a common one. The diagnostic fault codes did not say to replace the throttle position sensor. Fault codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is actually the cause of that code only about half of the time. You first have to rule out wiring and connector problems which in this case are much more common.

Be aware too that Chrysler makes reading fault codes yourself much easier than any other manufacturer. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the codes show up in the odometer display.

The reason live data is so valuable is because what you're describing is one symptom of a failing MAP sensor or a vacuum leak. The acceptable range of signal voltage is approximately 0.5 to 4.5 volts. Anything outside that range will trigger a fault code. The problem is a sensor that's just starting to fail can report the WRONG value that's still within that acceptable range. No fault code will be set but since a tenth of a volt change has a big effect of fuel metering calculations, an incorrect signal voltage will have a big effect on engine performance.

In the late '80s and early '90s MAP sensor failures were real common but they rarely took more than a few hours to go from poor engine performance to a total no-start condition. Once the sensor was redesigned, failures are not very common. I'd expect first to find a wiring problem, but that would set a fault code that would turn on the Check Engine light. Since the sensor's signal voltage isn't going out of range, I think I'd start by looking for a vacuum leak.

As far as injectors, that should be the last thing on your list of suspects. GM has a lot of trouble on high-mileage engines with mismatched injectors. Chrysler buys theirs from Bosch in flow-matched sets and they have extremely little trouble with them. Measuring resistance values isn't likely to identify a problem either. If one is partially-shorted, you might develop a misfire, which the Engine Computer would detect, and again, turn on the Check Engine light. All of them aren't going to fail at the same time so if you suspect a fuel-related cause, look to pressure and volume. Those aren't likely to be the cause here either because those typically cause stalling when the largest volume of fluid is flowing, which is, ... During coasting.
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Monday, March 30th, 2015 AT 5:39 PM

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