TPS Out Of Range
#1
05-07-2011, 08:56 AM
TPS Out Of Range
Hi everyone, I've been having problems with my 91 Blazer for a while now and I still can't figure out what the problem is. I'm hoping somebody can help.
The problem is a very rough idle and stalling if you slow down when driving. When this started over a month ago it would idle fine but spit and sputter when driving (like it had a bad miss). It will barely stay running on it's own at idle now.
Using the OBD I paperclip check, I'm now getting error code #21, which is the TPS out of range. I had already replaced the TPS thinking this might be the problem with the spitting and sputtering. When I install the TPS I have to turn it backwards slightly towards the firewall to get it to engage onto the blade on the end of the throttle shaft. I then have to turn it forward to align the holes to the throttle body. I still have the old TPS and it is exactly the same way, so I'm thinking they're either both wrong or this is the normal positioning. From what I see there is no adjustment for the unit. On the opposite side of the throttle body there is a set screw that acts as a stop on the throttle bracket. The head of this screw is towards the front of the truck and does not have a slot or hex head for position adjustment. Here's everything else that I've done prior to this point:
- New plugs and wires - Replaced the distributor cap and rotor
- Had the ICM checked twice, once cold and once hot (drove it to Autozone and pulled it in the parking lot) - Swapped in another coil (?) - Ran 1/2 a can of seafoam through the throttle body and put the other half in the oil - Put a can of seafoam in the gas tank - Pulled and cleaned the IAC valve - Checked the timing (it was right on, this was when it would still idle ok but was spiiting and sputtering when driving) - Performed a compression test on each of the cylinders (min 114 vs max of 126 but mostly in the 116 to 120 range).
I had the truck to a shop a month ago and it wasn't generating any codes then, but after doing the compression testing I decided to check it again, and now I have the code #21. Any help would be appreciated. Thanks.
The problem is a very rough idle and stalling if you slow down when driving. When this started over a month ago it would idle fine but spit and sputter when driving (like it had a bad miss). It will barely stay running on it's own at idle now.
Using the OBD I paperclip check, I'm now getting error code #21, which is the TPS out of range. I had already replaced the TPS thinking this might be the problem with the spitting and sputtering. When I install the TPS I have to turn it backwards slightly towards the firewall to get it to engage onto the blade on the end of the throttle shaft. I then have to turn it forward to align the holes to the throttle body. I still have the old TPS and it is exactly the same way, so I'm thinking they're either both wrong or this is the normal positioning. From what I see there is no adjustment for the unit. On the opposite side of the throttle body there is a set screw that acts as a stop on the throttle bracket. The head of this screw is towards the front of the truck and does not have a slot or hex head for position adjustment. Here's everything else that I've done prior to this point:
- New plugs and wires - Replaced the distributor cap and rotor
- Had the ICM checked twice, once cold and once hot (drove it to Autozone and pulled it in the parking lot) - Swapped in another coil (?) - Ran 1/2 a can of seafoam through the throttle body and put the other half in the oil - Put a can of seafoam in the gas tank - Pulled and cleaned the IAC valve - Checked the timing (it was right on, this was when it would still idle ok but was spiiting and sputtering when driving) - Performed a compression test on each of the cylinders (min 114 vs max of 126 but mostly in the 116 to 120 range).
I had the truck to a shop a month ago and it wasn't generating any codes then, but after doing the compression testing I decided to check it again, and now I have the code #21. Any help would be appreciated. Thanks.
#2
05-07-2011, 11:22 AM
That's the way the TPS goes in, you have to set it on the shaft and then rotate it to put the screws in. I would say if both are generating a code then there is something else wrong, maybe the wiring. I think a new connector end can be bought at any auto parts store or you could try a used one from a wrecking yard.
You can always check the resistance of the TPS first to rule that out before you swap the connector. Do a search on checking that, you'll need an ohm meter and the resistance specs.
You can always check the resistance of the TPS first to rule that out before you swap the connector. Do a search on checking that, you'll need an ohm meter and the resistance specs.
Last edited by Cidium; 05-07-2011 at 11:25 AM.
#3
05-07-2011, 05:36 PM
Thanks Cidium. I had already read through a bunch of the posts and I believe at WOT it should be 4 to 4.5 OHMs, but I can't remember what it should be when closed. I'll have to re-read some posts to be sure.
I'll try this and post back the results I get.
A couple of other things I forgot to mention in the already tried section:
- I changed the fuel filter
- The fuel spray at the throttle body is good
- When it was in the shop, the catalytic converter was replaced, probably $190.00 down the drain...
- Swapped in another spark control module I had off my old 89 Blazer
- Replaced the PCV valve and one of those damn plastic (emission control) hoses that was cracked
I'll try this and post back the results I get.
A couple of other things I forgot to mention in the already tried section:
- I changed the fuel filter
- The fuel spray at the throttle body is good
- When it was in the shop, the catalytic converter was replaced, probably $190.00 down the drain...
- Swapped in another spark control module I had off my old 89 Blazer
- Replaced the PCV valve and one of those damn plastic (emission control) hoses that was cracked
Last edited by coda56; 05-07-2011 at 05:47 PM.
#4
05-10-2011, 07:26 PM
I checked theTPS with my multimeter set on the 20 OHM scale, but never got a reading other than 1. I tried it with ignition turned on and then tried it again with the vehicle running. I back probed through the rubber seal on top of the TPS.
When I was done testing, I disconnected the TPS and started the truck. It ran better with the TPS disconnected than it does with it connected. It actually sat and idled fairly smoothly without having to jamb the long ice scraper between the seat and the gas pedal. Is my new TPS bad or did I somehow not test it correctly?
When I was done testing, I disconnected the TPS and started the truck. It ran better with the TPS disconnected than it does with it connected. It actually sat and idled fairly smoothly without having to jamb the long ice scraper between the seat and the gas pedal. Is my new TPS bad or did I somehow not test it correctly?
#6
05-12-2011, 02:53 PM
You are on the wrong setting, you should be checking voltage. Also make sure you are probing the signal wire not the 5V reference or the ground. Voltage on the TPS should be .5 at idle and 4.5 at WOT, but + or - .1V should still be acceptable. Also verify that the reference wire is providing 5V, if that is wrong then it could be causing your trouble code.
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