bog at 100% throttle, not at 95%

[lxadeuce]

like the title says, i have a hesitation when i'm cruising along at about 70mph in 4th, 5th or 6th and i punch the throttle to 100%. but if i push it to 100% and then just slightly let off, it accelerates much quicker. it feels to me like it's running too rich at 100% but but even after a couple seconds staying at 100%, it clears up and pulls as hard then as it does at the 95% mark. any ideas on how to fix this or what it could be? car is stock

 

[Slithr]

Brett, my guess is your throttle body needs to be cleaned? But, I'm sure some "real" experts will chime in soon.

 

[plumcrazy]

wires ?....

 

[99 R/T 10]

Plugs/wires first, but it could also be your TPS. Are you getting a CEL?

 

[Martin]

If you're getting the hesitation/rough running at 100% throttle and not at 95%, it's WOT related, and occurs when the computer goes into 'open loop' mode. When the computer goes into 'open loop' it's basically ignoring a bunch of sensor inputs and injecting fuel according to a pre-set fuel mapping that's a lot richer than 'closed loop.'

As noted above, the first thing to do is check the simple things like throttle body cleanliness. Also check simple things like the air filter and the plugs. If it were me, I'd put a bottle of injector cleaner in the tank and see if that helps (Techron or Red Line SI-1 are my favorites).

The year also matters, as I'm sure some will chime in

If simple things don't sort this out, the next things to look at are the throttle position sensors and throttle cable adjustments. Depending on the year of the car, you might have one sensor thinking it's in WOT mode, and the other at 95% - which can confuse the computer and cause some stumbling.

 

[lxadeuce]

If you're getting the hesitation/rough running at 100% throttle and not at 95%, it's WOT related, and occurs when the computer goes into 'open loop' mode. When the computer goes into 'open loop' it's basically ignoring a bunch of sensor inputs and injecting fuel according to a pre-set fuel mapping that's a lot richer than 'closed loop.'

As noted above, the first thing to do is check the simple things like throttle body cleanliness. Also check simple things like the air filter and the plugs. If it were me, I'd put a bottle of injector cleaner in the tank and see if that helps (Techron or Red Line SI-1 are my favorites).

The year also matters, as I'm sure some will chime in

If simple things don't sort this out, the next things to look at are the throttle position sensors and throttle cable adjustments. Depending on the year of the car, you might have one sensor thinking it's in WOT mode, and the other at 95% - which can confuse the computer and cause some stumbling.

ok, the car is a 96 GTS. I just put in a bottle of injector cleaner and i changed the plugs and wires yesterday. the throttle body was cleaned about 4 months ago when i had it off. i was wondering if it was some type of sensor that may cause this. i guess it could be the throttle cable but is that adjustable on this year model?

 

[Martin]

Hopefully it's just gunked up injectors. In case that doesn't solve it, here are some additional troubleshooting questions:

How many miles, and are the cats still stock? Also, when you removed the throttle bodies for cleaning, did you remove the throttle position sensor? Finally, did you put the 'synchronization' bar back exactly as it was (with the little dab of white paint still on the synchronization screw)?

A couple of things come to mind - the cats could possibly be on their way out. If they're partially plugged, you can sometimes get that WOT bog until they heat up enough and burn the gunk out.

If you removed your throttle bodies, you could have messed up the throttle position sensor. It's easy to check with a voltmeter as follows: turn key to 'on' (but obviously don't start the car), connect the hot side of the voltmeter to the middle conductor (and the other to ground, of course). At the 'idle setting', the sensor should read somewhere around a half volt or so. At wide open throttle, it should read about 4 volts. If someone has the service manual handy, they can give you the exact values - those are what I remember from past trouble-shooting. I think there's an 'acceptable range' that the manual provides.

Finally, if you 'broke the seal' on the synchronization bar screw, there's a chance you might have one throttle body opening up more than the other. That would normally lead to all kinds of driveability issues (bucking, etc.), but it is something to consider.

All in all, probably something minor. Even at 15 years old, these cars are pretty bulletproof.

 

[KNG SNKE]

Stock car or modded?

 

[Jack B]

Your assessment of 95% may not be accurate, you should hook up an OBD tool to verify the actual numbers. In addition, the engine goes into open-loop well before 95% throttle. It probably doesn't matter, in either case it appears you are in open-loop. In affect, a predefined fuel/load/rpm table is running the engine.

If it is ignition related a wideband a/f log will show excessively lean at your trouble point. You will see large lean spikes on the log. If it is fuel you it could show lean or rich, but, probably will not see the large short time deviations. If you try to isolate the problem via the a/f, you must make sure that the a/f software averaging is shut off or at a minimum.

Good luck with the trouble shooting.

 

[DrumrBoy]

I've seen trouble at WOT when the PCM learned that position with the carpet in and then the driver took the carpet out (because you now will go past the originally "set" WOT position).

I don't think this is your issue, but if you did mess around with the carpet or put new mats in, you might want to reset the PCM ad teach it where the real WOT position is.

If you made no changes to the carpet, ignore this post! Just another variable.

 

[lxadeuce]

I've seen trouble at WOT when the PCM learned that position with the carpet in and then the driver took the carpet out (because you now will go past the originally "set" WOT position).

I don't think this is your issue, but if you did mess around with the carpet or put new mats in, you might want to reset the PCM ad teach it where the real WOT position is.

If you made no changes to the carpet, ignore this post! Just another variable.

to reset the PCM i diconnect the positive cable from the battery and ground it, is that correct?

 

[Catwood]

I'd check Voltage on the TBS. Sweep it with the car off, key on and see what happens,

 

[agentf1]

I am NO expert but I have always heard if you do not have a really good battery it can cause different drivability issues.

 

[DrumrBoy]

to reset the PCM i diconnect the positive cable from the battery and ground it, is that correct?

That's the start of it. Once power is restored, there's a specific procedure for teaching the PCM where WOT is. It involves turning the key to the On position and slowly depressing the go pedal to the floor and back a couple of times. Apologies for being vague on the specifics, I have it written down but its in the car and not here at the moment.

Perhaps others with better memories can chime in on the specifics.

Its an easy thing to check, but unless you've lost power or changed the carpets, there's no reason for this to wig out.

Best of luck with the remedy.

 

[lxadeuce]

Hopefully it's just gunked up injectors. In case that doesn't solve it, here are some additional troubleshooting questions:

How many miles, and are the cats still stock? Also, when you removed the throttle bodies for cleaning, did you remove the throttle position sensor? Finally, did you put the 'synchronization' bar back exactly as it was (with the little dab of white paint still on the synchronization screw)?

A couple of things come to mind - the cats could possibly be on their way out. If they're partially plugged, you can sometimes get that WOT bog until they heat up enough and burn the gunk out.

If you removed your throttle bodies, you could have messed up the throttle position sensor. It's easy to check with a voltmeter as follows: turn key to 'on' (but obviously don't start the car), connect the hot side of the voltmeter to the middle conductor (and the other to ground, of course). At the 'idle setting', the sensor should read somewhere around a half volt or so. At wide open throttle, it should read about 4 volts. If someone has the service manual handy, they can give you the exact values - those are what I remember from past trouble-shooting. I think there's an 'acceptable range' that the manual provides.

Finally, if you 'broke the seal' on the synchronization bar screw, there's a chance you might have one throttle body opening up more than the other. That would normally lead to all kinds of driveability issues (bucking, etc.), but it is something to consider.

All in all, probably something minor. Even at 15 years old, these cars are pretty bulletproof.

i just checked the TPS, i got .8 at closed throttle, 3.8 at wide open. i have looked all over but can't find the acceptable range