Engine boggs on low rpm acceleration
08-24-2014, 01:00 AM
#1
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Year: 90'
Model: Cherokee
Engine: 4.0
Engine boggs on low rpm acceleration
1990 jeep cherokee 4.0
This just happened about a month ago. It first started when I pulled to a stop sign and it about stalled on me. Again later down the road when I put it into reverse it almost stalled. Now its the same when I'm driving at low rpms, like at a stop. When I go to accelerate it typically boggs down and nearly stalls less I fenangle the throttle. I've done a little reading and most posts I come accross address the issue but don't resolve with a solution so I'm gonna put this one out there one more time.
I have redone the engine grounds some time ago, cleaned out a great majority of all engine connections and still haven't a clue. Could someone please help narrow this down with me? Heres a video of the clunkiness.
This just happened about a month ago. It first started when I pulled to a stop sign and it about stalled on me. Again later down the road when I put it into reverse it almost stalled. Now its the same when I'm driving at low rpms, like at a stop. When I go to accelerate it typically boggs down and nearly stalls less I fenangle the throttle. I've done a little reading and most posts I come accross address the issue but don't resolve with a solution so I'm gonna put this one out there one more time.
I have redone the engine grounds some time ago, cleaned out a great majority of all engine connections and still haven't a clue. Could someone please help narrow this down with me? Heres a video of the clunkiness.
08-24-2014, 06:00 AM
#3
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Before I go ahead with the following, I see you have a Renix, and I'm always wrong with those. Cruiser54's Mostly Renix Tips is a roadmap through the wasteland of Renix Issues that gives you a chance to make it through those alive. Find the link in his signature (or in DFLinstone's).
So, having said this, let's take a second and look at some background on this (besides the nice squeeks from the pulley's) just for diagnostics sake.
You open the throttle at idle, your engine stalls. When you open the throttle, what you do is " add more air" to the air/fuel mix. This will need to be followed by the PCM "adding more fuel", otherwise your engine stalls and you'd never be able to accelerate.
The "add more fuel" depends on a few factors and your PCM needs info from things like sensors to determine how much fuel needs to be added. One of the sensors that are involved in this are the TPS (throttle position sensor) and MAP. Faulty sensors give wrong or no info to the PCM, and as a result could lead to the stalling.
The amount of air that is regulated at idle (your 'starting position') flows via the IAC. A dirty/stuck/not proper functioning IAC can cause idle issues, and is related to the throttle body and TB valve. These items could be involved in your issue as well, or add to it. And so is a throttle cable mal adjustment
Also possible; supply can't meet demand. Fuel delivery is another thing in the equation. And your year has a fuel filter.
In a nutshell: several things can cause this stalling when opening throttle at idle.
What I would do:
1) Clean IAC, throttle body and especially area of TB valve
2) replace fuel filter (cheap and easy)
3) Take fuel pressure (at idle)
4) Check your TPS (measure voltage and IIRC the Renix's TPS needs adjusting as well)
5) Adjust TV cable (throttle, not television)
6) Drop a bottle of injector cleaner in the tank (because you need to do somewhat of a ritual thing that makes you believe everything will smooth out now)
MAP sensor I'd just replace, but like stated in the beginning: I'm not familiar with RENIX years regarding this.
Just an idea on what do to first when an issue like this occurs.
Before I continue with chapter 2, ....let's first see how the above goes?
So, having said this, let's take a second and look at some background on this (besides the nice squeeks from the pulley's) just for diagnostics sake.
You open the throttle at idle, your engine stalls. When you open the throttle, what you do is " add more air" to the air/fuel mix. This will need to be followed by the PCM "adding more fuel", otherwise your engine stalls and you'd never be able to accelerate.
The "add more fuel" depends on a few factors and your PCM needs info from things like sensors to determine how much fuel needs to be added. One of the sensors that are involved in this are the TPS (throttle position sensor) and MAP. Faulty sensors give wrong or no info to the PCM, and as a result could lead to the stalling.
The amount of air that is regulated at idle (your 'starting position') flows via the IAC. A dirty/stuck/not proper functioning IAC can cause idle issues, and is related to the throttle body and TB valve. These items could be involved in your issue as well, or add to it. And so is a throttle cable mal adjustment
Also possible; supply can't meet demand. Fuel delivery is another thing in the equation. And your year has a fuel filter.
In a nutshell: several things can cause this stalling when opening throttle at idle.
What I would do:
1) Clean IAC, throttle body and especially area of TB valve
2) replace fuel filter (cheap and easy)
3) Take fuel pressure (at idle)
4) Check your TPS (measure voltage and IIRC the Renix's TPS needs adjusting as well)
5) Adjust TV cable (throttle, not television)
6) Drop a bottle of injector cleaner in the tank (because you need to do somewhat of a ritual thing that makes you believe everything will smooth out now)
MAP sensor I'd just replace, but like stated in the beginning: I'm not familiar with RENIX years regarding this.
Just an idea on what do to first when an issue like this occurs.
Before I continue with chapter 2, ....let's first see how the above goes?
08-26-2014, 07:37 AM
#6
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basic maintenance should always be done, including cleaning sensors with the proper fluids / techniques. Many times that eliminates the problems. Bogging like that could very well be one of the sensors not working or on its way out. Does it repeat the stall or bog every time, whether or not the engine is cold or hot?
08-27-2014, 09:32 PM
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Roller, Gotcha!
CC, I've done a few of the things that Cruiser recommends such as bettering the grounds and cleaning all electrical contacts. Very few were heavily corroded.
I need to get a few testers like a fuel pressure tester and compression tester to do those types of tests as well as a vacuum pump to test the MAP. I'm busy for the next seven days but next weekend I should have replaced a few sensors and the vacuum line tree.
To answer your question, it bogs down at a stop, low RPM's, hot or cold and its more often than not. Some times I'll get the green (traffic) light and it wont hesitate or bog. I just topped of the oil ( it was at add) and also flushed the engine after a 3 day Prestone cleaner treatment (replaced w/ 50/50) and it seems like its dampened the issue, but not wholly. Im curious if a Seafom application will help clean out some engine gunk to aid my issue.... but I'm still certain that the leading cause is sensor related. Will keep you guys posted, thanks for the responses.
CC, I've done a few of the things that Cruiser recommends such as bettering the grounds and cleaning all electrical contacts. Very few were heavily corroded.
I need to get a few testers like a fuel pressure tester and compression tester to do those types of tests as well as a vacuum pump to test the MAP. I'm busy for the next seven days but next weekend I should have replaced a few sensors and the vacuum line tree.
To answer your question, it bogs down at a stop, low RPM's, hot or cold and its more often than not. Some times I'll get the green (traffic) light and it wont hesitate or bog. I just topped of the oil ( it was at add) and also flushed the engine after a 3 day Prestone cleaner treatment (replaced w/ 50/50) and it seems like its dampened the issue, but not wholly. Im curious if a Seafom application will help clean out some engine gunk to aid my issue.... but I'm still certain that the leading cause is sensor related. Will keep you guys posted, thanks for the responses.
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08-27-2014, 09:35 PM
#8
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BIlly Boy, Not really sure its the throttle cable because of the few things I've done lately that's lessened the severity of my problem. How do you check for cable integrity? I have a Haynes manual, perhaps its listed in there.
08-28-2014, 07:12 AM
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when you slow down and idle, the IAC takes over. If its not functioning properly and the RPM is low, then when you hit the gas it may be dumping in fuel too fast for the engine to handle at low rpm, giving you the stumble / bogg until it catches up with enough air. Could be lots of things, but I'd figure the IAC is somehow involved (especially considering how often we see posts about them going south).
09-11-2014, 05:20 PM
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I just replaced the MAP and almost no change at all. I just got my fuel pressure tester so I'm going downstairs to do that, as well as a compression test (Just for ****s and giggles) but I'll be cleaning the TB and IAC as well. I just replaced that item (IAC) like a year ago... wouldn't put my money on that.
I'll also look into replacing the fuel filter today or tomorrow as well.
I'll also look into replacing the fuel filter today or tomorrow as well.
09-11-2014, 06:30 PM
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Year: 1999
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1. Replace fuel filter. They're cheap
2. Definitely test fuel pressure! For your vintage, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Check the vacuum line leading to the FPR; if it is wet with raw fuel, you have a ruptured diaphragm on your regulator.
3. Test your throttle position sensor (see below for Cruiser's procedure)
4. Thoroughly clean throttle body and idle air control (bench cleaning is best)
5. Probably not tuneup hardware related, but for good measure, when was the last time you replaced plugs, wires, distributor cap and rotor?
6. Drink beer
------------------------------------------------------------------------------
RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS, there are two things that need to be done.
1) Be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.
TPS ADJUSTMENT FOR ENGINE ISSUES
Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.
Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.
TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES
RENIX automatic transmission equipped XJs and MJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.
For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced. The square 4 wire connector is just not used.
2. Definitely test fuel pressure! For your vintage, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Check the vacuum line leading to the FPR; if it is wet with raw fuel, you have a ruptured diaphragm on your regulator.
3. Test your throttle position sensor (see below for Cruiser's procedure)
4. Thoroughly clean throttle body and idle air control (bench cleaning is best)
5. Probably not tuneup hardware related, but for good measure, when was the last time you replaced plugs, wires, distributor cap and rotor?
6. Drink beer
------------------------------------------------------------------------------
RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS, there are two things that need to be done.
1) Be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.
TPS ADJUSTMENT FOR ENGINE ISSUES
Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.
Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.
TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES
RENIX automatic transmission equipped XJs and MJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.
For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced. The square 4 wire connector is just not used.
Last edited by tjwalker; 09-11-2014 at 06:33 PM.
09-11-2014, 09:27 PM
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when you slow down and idle, the IAC takes over. If its not functioning properly and the RPM is low, then when you hit the gas it may be dumping in fuel too fast for the engine to handle at low rpm, giving you the stumble / bogg until it catches up with enough air. Could be lots of things, but I'd figure the IAC is somehow involved (especially considering how often we see posts about them going south).
09-12-2014, 12:08 PM
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PROBLEM RESOLVED:
I randomly wanted to replace the vacum harness' so when I had the Intake off to clean the TB, I was pulling vac lines off. When I got to the EGR, somehow I decided to turn over the vacuum actuator. Well, let the photo do the talking. Needless to say, this fixed the problem. I can't imagine how it happened, but she throttles like an adolescent ready to trot. Zero bogging issues at idle gassing. Thanks all for the looks!
Cruiser, will still do all the other recommendations. Oh, wires and plugs replaced just over a year ago. Will swap plugs and rotor soon. How did you do your wire set up? it looks really clean and cool. If that is your jeep from the video you linked to me about the flexplate, fix that is.
I randomly wanted to replace the vacum harness' so when I had the Intake off to clean the TB, I was pulling vac lines off. When I got to the EGR, somehow I decided to turn over the vacuum actuator. Well, let the photo do the talking. Needless to say, this fixed the problem. I can't imagine how it happened, but she throttles like an adolescent ready to trot. Zero bogging issues at idle gassing. Thanks all for the looks!
Cruiser, will still do all the other recommendations. Oh, wires and plugs replaced just over a year ago. Will swap plugs and rotor soon. How did you do your wire set up? it looks really clean and cool. If that is your jeep from the video you linked to me about the flexplate, fix that is.