This is the truck that was Dad's (RIP). I drove it home from E. Oregon last summer, towing a car on a trailer, without a hitch. Then it sat all winter. I tried to start it back when we had the big freeze, cause it has better tires than mine, but it would not crank.

So here's where I'm at. I've checked and cleaned up all the battery terminals and connections. I can turn the key on and everything comes alive like it should. Dash warning lights, radio, heater fan, the works. I can turn the key over to start and everything acts like it should but it won't crank. I can leave the key on, go around front and jump the hot lug on the starter relay to the coil lug and it'll crank right over and start.

I have the factory service manual subscription from AllData. From what I'm seeing in the diagrams, power comes off the hot lug on the solenoid, over to the power distribution block, through a fuse (that I did check), through the ignition switch, through the clutch safety switch if you have a manual, or through a jumper if you don't. (I don't), through the Transmission Range Sensor if you have an automatic (I do), to the wire that connects to the relay lug. I'm not getting any power to that wire. So I think I'm down to either the ignition switch or the Transmission Range Sensor.

So today I figured I'd try to get to the Transmission Range Sensor. The ignition switch is pretty new and easier to get to, but I figured if I could get the sensor plug off and check for power on the start circuit to it, I could kill two birds with one stone. So far I haven't figured out how to get that damn plug off. But that led me to another problem.

I decided it'd be easier to work under there if I put the front up on ramps. So I got out my ramps, put them in place, locked the hubs and put it in 4WD, got it started, put it in drive and gave it a little throttle and nothing happened. No throttle response at all. I swear I can't catch a break.

Now I need a little help diagnosing. I haven't looked at the manual yet but I know there is a throttle position sensor and an idle switch. (I think there's an idle switch). I think the best way to diagnose this is going to be to get the OBD connector and download Forscan. So my first question is, which connector do people prefer. I've never used this software before, I used to have a license for AutoEnginuity, but it's long expired and I think to renew it I'd have to upgrade that connector. It sounds like Forscan would be easier.

There are two mentioned on the Forscan website. The OBDLink EX is $60 (give or take) on Amazon and I can get it overnight. The Vgate vLinker FS is only $35, but I can't get it until the 15th to the 17th. I'd appreciate any feedback people might have with good reasons why I might prefer one over the other.

My other question... I know if the Throttle Position Sensor is malfunctioning that you won't get throttle response. Is there anything else, like any other engine error condition that would cause the engine to stay at idle even though I'm stepping on the go pedal? This is why I'm thinking to get the software. To check for codes and I assume you can see live data like I used to with AutoEnginuity to see what's going on with the TPS.

Thanks ahead for any advice.

David Chamberlain

 

It sounds like you’re on the right track to me. One thing I might add is that I would imagine that an idle validation switch malfunction could cause lack of throttle response.

 

I don't have any input on another cable, but I'm using the Vgate vLinker FS and it's working well with ForScan to do both scans and datalogs on the road on a Windows laptop.

 

could be starter relay or bad ground on it
sometimes the PCM output goes bad, check its pin for power change

IVS can be cleaned with contact cleaner and bent back to where it needs to go if not set right
There is a way to make the PCM re learn the pedal
To recalibrate the PCM and accelerator pedal, the ignition switch must be in the ON position and then the accelerator pedal must be slowly and fully depressed from idle to full throttle. Repeat the procedure three times. Procedure complete.

 

Thanks. I'm pretty sure the starter relay is OK, because I can turn on the key and jump the hot post of the relay to the coil post (the one where the little wire connects) and it'll crank right over and start. So the relay has to be closing and providing the power to the starter.

The information about re-calibrating the pedal is good. I didn't know that and I'll try it.

 

So... continuing the saga of trying to diagnose the no throttle response problem.

I got the OBDLink EX cable from Amazon yesterday. I had tried a much cheaper Bluetooth adapter that someone had recommended in another thread, but it wouldn't pair to my laptop, so rather than fight it (I've found Bluetooth anything can be really finicky sometimes), I went ahead and opted for the USB cable.

The only code I pulled was P0603, "Internal Control Module KAM error." Which makes sense being I had the batteries disconnected early on in the starting diagnosis process cleaning up the terminals. That means any other codes that might've helped me are gone.

So I pulled up live data on the Throttle Position Sensor and the Idle Validation Switch. With no foot on the pedal, the TPS sensor was bouncing around 10%, but the IVS showed "NOT IDLE" or something like that. When I pushed the pedal all the way down the TPS went up to somewhere around 75 to 80% (I don't remember exactly, I was more honed in on the IVS never switching to idle.) Nothing I could do with the pedal could get that PID to switch to IDLE.

But, when I pushed the pedal down enough to get the tab out of the way, and pushed on the switch with my finger, I could hear the switch click and the PID changed to IDLE. So the switch is working.

It appears, for some reason, that the tab that pushes on that switch isn't quite pushing down far enough. I'm assuming that because that switch never closes, the computer has put it into some sort of limp mode and won't allow it off of idle. I don't see how that tab could have bent, or how the switch could have moved, or anything. Perhaps just wear on the switch has moved the internals a little, causing it to be just a hair short of closing.. When I looked around online, it appears that you can't buy that switch. You can buy whole pedal assemblies for around $200, and you can buy the Throttle Position Sensor. But not the Idle Validation Switch.

I debated for awhile on how I could fix this thing. I could try to bend the tab a little, but that looks like it might be difficult. I don't want to beat on it or reef on it because for sure I'd break something. So then I had an idea. I've got a pretty good selection of shrink tubing that I bought last summer for other projects, ranging from tiny to enormous. I have some that would slide over that tab. If I could find a very thin (Like 1/16th or even less) piece of metal or hard plastic I could shrink tube it to that tab. In fact, when I was looking at it and selecting a piece of tube that I thought would work, just the thickness of the shrink tube was enough to cause that switch to click when I let the throttle down.

I think this is a viable fix for this problem. I'd be interested in opinions. I'd also like to know if anyone knows if the 10 to 75ish% I'm seeing on the TPS is normal, or if that's another part of the problem. Not going from 0 to 100%

Thanks in advance. And here is a picture I took of it if it helps to make what I'm saying make sense.