87 4x4 305 TBI Code 24

[87scottsdale]

Ok I have been looking all day to try and find a solid starting point on figuring this code out.

I can unhook battery to clear code 24,drive 8 miles and comes back.

Speedometer is fully functional,(NO Cruise in this truck)

I have checked connection on the VSS buffer. (Cleaned contacts)

What throws me off is a 100% functional speedometer.

Truck is lifted with 35" tires 305 TBI/700R4. No other codes present and wanting to get this fixed to be able to move onto other issues..

Please Help!!

[DnStClr]

The throttle position sensor can be out of adjustment and will throw a code 24. From your troubleshooting it doesn't sound like the vss is at fault.
Here's how to check the tps voltage= I got it from another website.
       
        1.Open the hood on the truck. Remove the engine's air cleaner by removing the wingnuts. Locate the TPS sensor on the passenger side of the throttle body. Unplug the harness connected to the TPS sensor.
        2. Place the black probe from the voltmeter on the middle terminal inside the TPS. Place the voltmeter's red probe on the the top, rearward terminal of the TPS.
        3. Put the key in the ignition. Turn the key to the "on" position, but do not start the engine.
        4. Look at the voltmeter. The voltage should read between 0.5 and 1.2 volts when the throttle body is closed. Turn the throttle linkage by hand, opening and closing the throttle body. Watch the voltmeter to ensure voltage moves up and down in conjunction with the movement of the throttle body. The TPS sensor must be replaced if the voltmeter spikes.

oops- 2nd edit!  I forgot to add-if the voltage doesn't meet the specs, the tps is faulty and needs to be replaced. On our trucks they aren't adjustable.

[87scottsdale]

The throttle position sensor can be out of adjustment and will throw a code 24. From your troubleshooting it doesn't sound like the vss is at fault.

Is there a particular procedure for adjusting? I hear you need to modify mounting holes for adjustment..

Edit:

I assume I will be looking for .5v-4.5v as with any other TPS adjustment?

[DnStClr]

Yes-those are the voltages that you should look for as the throttle plate is turned.

[87scottsdale]

Ok. TPS was out of spec. .3v closed and 3.8v open. So got that fixed at .5v closed 4.1 open. Truck really does run a lot better now.

Took the truck for a test drive. sure enough 8 miles SES light. Got home checked code and sure enough Code 24 again.

Anything else to test/look at?

Thanks for the help so far..

[DnStClr]

hmm- did you check( visual) the wiring between the tps and the ecm? Connectors look ok?
Is the truck shifting ok?  The tps is a potentiometer, and it can work ok but still have a dead spot in it, where 0 volts are detected by the ecm, and then a code gets set. But it might be working at the lower and higher ends, so you see the correct voltages there and still have a bad sensor. Most car techs use an oscillascope to check them.
That's about all i know about them.
The problem might still be in the vss- the speedo cable,transmission speed sensor system and wiring. I don't have a 4wd, so I'm not sure whether the transfer case is involved or not. not much help, huh?

[87scottsdale]

hmm- did you check( visual) the wiring between the tps and the ecm? Connectors look ok?
Is the truck shifting ok?  The tps is a potentiometer, and it can work ok but still have a dead spot in it, where 0 volts are detected by the ecm, and then a code gets set. But it might be working at the lower and higher ends, so you see the correct voltages there and still have a bad sensor. Most car techs use an oscillascope to check them.
That's about all i know about them.
The problem might still be in the vss- the speedo cable,transmission speed sensor system and wiring. I don't have a 4wd, so I'm not sure whether the transfer case is involved or not. not much help, huh?

Plenty of help. Truck shifts a lot better than what it did. Another thing I am fixing is the O2 sensor after installing long tube headers. I need to order the heated sensor for it. The truck was not all that well taken care of but anything important wiring is undisturbed.

All TBI connections are good. No corrosion on pins etc. TPS readings were very smooth and linear.


The transfer case has the speedometer cable running from it. So what I am thinking is since my speedometer is basically cable driven my it will still work 100% even if the ecu is not getting proper signal from the VSS buffer.

I actually have another VSS buffer I am going to try and see if that could be the fix. If not I will have to find a diagram for ECM-VSS wiring and spec everything out..

[Captkaos]

It sounds like your VSS is bad.  This is the code conditions: What happens if you put it in drive, bring the idle up to 1600rpms and wait for 10 seconds?
 
 Code 24- A vehicle speed sensor malfunction will set this code. The conditions for it being set is vehicle speed at 0 mph, engine speed between 1500-3000 rpm, tps less than 2% open, and the transmission not in park or neutral. These conditions must be met for about 10 seconds. A faulty VSS will affect the operation of the TCC, IAC and ignition timing.

[87scottsdale]

Ok well changed buffer this morning. Disconnected battery terminal and went for a drive. So far no code. Runs a whole lot better. I need to address the O2 issue because I am having problems low loads and wanting to hesistate/bobble.

I need to order this sensor get it hooked up and see what changes. I will report back on my code 24 issue as well..

[87scottsdale]

Well it does look as if the Code 24 problem has been solved. I am having some stumbling/shuddering while driving. I recheck TPS sensor to see if it had moved since I modified the mounting holes to get .5v. My intial setting of it has not changed.

I looked inside TBI and also set my TV cable as I had not done that since the Headgasket was replaced.

TBI is fairly nasty so I think I am going to pull it this weekend and give it a thorough cleaning and new gaskets..

I will report any other findings..

[87scottsdale]

Completely overhauled TBI today. Thorough cleaning new FPR diaphram,all new gaskets etc. Somewhat improved but not a whole lot. Really need this O2 now and a fuel pressure gauge to monitor Fuel pressure.

Any recommendations for adapters? I have a marshall liquid filled gauge,but not sure how to adapt it to the factory TBI fuel lines.

[bd]

If you have a timing light: first, verify your base timing (with the EST connector unplugged); second, connect the timing light to the coil wire and run the engine while aiming the light at the fuel spray from the injector nozzles to check for a distorted spray pattern.

-----------------------

Concerning your question on connecting your fuel pressure gauge, you can use the gauge adapter linked and shown below, modified with a 1/4" SAE flare fitting containing a Schrader valve and service cap, an R12 A/C hose, and the pressure gauge you already have.  It's not the least expensive solution, but it's clean, safe and works consistently well by temporarily substituting for the fuel filter. 

http://www.toolsource.com/fuel-injection-fuel-pressure-adapter-p-62179.html

If you have a 45° double flaring tool, a cheaper and permanent fuel pressure gauge tap is to cut the fuel supply pressure line where it's accessible and insert a double flare 'tee' fitting and 1/4" SAE flare fitting containing a Schrader valve, and hook up the gauge as outlined above.

[87scottsdale]

If you have a timing light: first, verify your base timing (with the EST connector unplugged); second, connect the timing light to the coil wire and run the engine while aiming the light at the fuel spray from the injector nozzles to check for a distorted spray pattern.

-----------------------

After replacing everything I have checked and reset base timing to *0. I had to pull distributor due to broken cap bolt..

I will check for pattern today when I get back over to my brothers garage.. I like the idea for that adapter. I may see what I can find at a local hardware store and try to throw it together.

[87scottsdale]

Would this just be cheaper and easier since I have an 1/8" NPT threaded fuel gauge already?

http://www.jegs.com/images/photos/300/361/361-100199.jpg

[bd]

That is an AN style in-line fitting based on a 37° flare.  It's not compatible with factory tube and o-ring fittings.  It won't work with your system by itself.