JeepForum.com

JeepForum.com (http://www.jeepforum.com/forum/)
-   YJ Wrangler Technical Forum (http://www.jeepforum.com/forum/f12/)
-   -   What's causing rpm to raise? (http://www.jeepforum.com/forum/f12/whats-causing-rpm-raise-1249826/)

provinT13 08-07-2011 03:09 PM

Cruise control redline!!!!
 
*EDIT* (I had made this thread originally on the symptoms he was describing, but now I got to see what was really happening so I am editing it)

My friend was describing a few problems he was having with his 1991 Sahara YJ, 4.0L, manual trans. I got a chance to drive it and this is what is happening. When cruise control is on, and he puts it in reverse, with the clutch still depressed, the cruise control takes over and opens the throttle all the way to red line. The only way to kill it is to take it out of reverse. With cruise control off this does not happen and it is only in reverse. He had a friend put on some tail light guards on a day before this started happening. I looked at his work and he had cut the wires to the lights, didn't re-crimp them, and just taped the wires back together. I figured something was getting crossed at the reverse lights so we re-wired everything correctly but it is still happening when he puts it in reverse. For now I have unhooked the cruise control linkage, but I need to know how to chase down this electrical problem. They must have fried something when they taped the wires back together because they were touching, maybe something with the reverse lights since it only happens in reverse? Something is telling the cruise control to give it more gas when it shouldn't be. Is there a relay or something that may be stuck? I don't know much about the YJ cruise control system.

Noltz 08-07-2011 03:26 PM

Easy thing to check on is the IAC being sticky. Use some throttle body cleaner in park and see if it cleans up at all.

roklok 08-07-2011 07:40 PM

Quote:

Originally Posted by noltz (Post 11982631)
easy thing to check on is the iac being sticky. Use some throttle body cleaner in park and see if it cleans up at all.

iac?

R3V413 08-07-2011 09:37 PM

Quote:

Originally Posted by roklok (Post 11983763)
iac?

Idle air Control Valve. They are normally mounted right before the throttle body, but I dont think the 91's have an IAC. The only thing that comes to mind is a vacuum leak, or sticky EGR valve. Make sure you check ALL the vacuum lines for hole, cracks or even dry rot. With the EGR valve, you can check it by letting the vehicle warm up, and when it is place 2 fingers on each side of the valve and have another person hit the accelerator and hold it at 1500 RPM. While they are doing this, you need to feel to see if the diaphram of the valve is moving up due to vacuum. If it isnt then push up on it with all 4 of ur fingers and it should start to run rough or even stall. If not then you need to replace the valve. If you dont feel it move then its not getting vacuum, but if it dont make the engine run rough or stall then its not holding vacuum. Make sure you check the lines before you check the valve.

Good Luck with it!

provinT13 08-11-2011 04:15 PM

He told me a friend said it was the tps sensor, it will be over here Saturday so I will get a good look then thanks guys

oldtime_ironman 08-11-2011 05:26 PM

Quote:

Originally Posted by R3V413 (Post 11984457)
Idle air Control Valve. They are normally mounted right before the throttle body, but I dont think the 91's have an IAC. The only thing that comes to mind is a vacuum leak, or sticky EGR valve. Make sure you check ALL the vacuum lines for hole, cracks or even dry rot. With the EGR valve, you can check it by letting the vehicle warm up, and when it is place 2 fingers on each side of the valve and have another person hit the accelerator and hold it at 1500 RPM. While they are doing this, you need to feel to see if the diaphram of the valve is moving up due to vacuum. If it isnt then push up on it with all 4 of ur fingers and it should start to run rough or even stall. If not then you need to replace the valve. If you dont feel it move then its not getting vacuum, but if it dont make the engine run rough or stall then its not holding vacuum. Make sure you check the lines before you check the valve.

Good Luck with it!

Just FYI the 1991's *do* have an IAC in the throttle body. But other than that, your post is spot-on.

provinT13 08-11-2011 06:34 PM

I didn't think there was an EGR valve on the fuel injected 4.0L

R3V413 08-11-2011 11:58 PM

Quote:

Originally Posted by provinT13 (Post 12007259)
Is there anything that sticks out of it only acting up in in 1st and reverse gears? I didn't think there was an EGR valve on the fuel injected 4.0L

Yes there an EGR valve, it is mounted on the intake manifold. And if it is a TPS problem, it would constantly be reving up when at an idle state, no matter what gear your in. One thing that I forgot to mention before, is a real easy way to check your vacuum lines (besides a visual inspection) is you can spray brake cleaner, carb cleaner, starting fluid, or anything of that sort on the line and if you hear it rev up, then you know where your leak is.

pasinbuy 08-12-2011 07:38 AM

Quote:

Originally Posted by R3V413 (Post 12008967)
Yes there an EGR valve, it is mounted on the intake manifold. And if it is a TPS problem, it would constantly be reving up when at an idle state, no matter what gear your in. One thing that I forgot to mention before, is a real easy way to check your vacuum lines (besides a visual inspection) is you can spray brake cleaner, carb cleaner, starting fluid, or anything of that sort on the line and if you hear it rev up, then you know where your leak is.

Brake cleaner and carb cleaner, are ok to use.

I would never use starting fluid, way too dangerous.

Que89YJ 08-12-2011 01:06 PM

No egr on the Multi port fuel injections, only on our Throttle body injections. See if its really spiking or if the rpm indicator is pegging. I would check the crank sensor. It gives the output for the RPM. I bet its loose or going bad.

provinT13 08-13-2011 10:04 AM

Turns out it's the cruise control, I have edited the OP

provinT13 08-13-2011 05:11 PM

bump


The time now is 03:40 PM.

Powered by vBulletin Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.