Hi, could use some help diagnosing an issue on a 2001 with a TRD supercharger running a Unichip piggy back controller. It ran fine for years and thousands of miles, then started throwing codes for throttle position sensor failure, P0120/P0121. My son has been driving it for the past couple of years, and he brought it to two shops who both recommended replacing the throttle body and TP sensor, which we did. It ran fine for maybe 1000 miles or so, then the codes came back, along with “rich bank 1/2” codes P0172/P0175. Other symptoms are an intermittently surging idle, smell of fuel, and hissing when you open the fuel cap.
I’ve been saying all along I think it’s actually an EVAP system issue, but I’m an old American V8 hotrod guy who doesn’t really understand that system at all!
. Here are my naive thoughts though, tell me if it makes any sense: When I did the supercharger build I accidentally broke the ear/inlet port off the air box where the EVAP vac connects, and temporarily ran a smaller line to a smaller, unused inlet on the box with plans to fix it later. Then I got caught up doing other things, quit driving the truck, and forgot about it. So when the problems started the first thing I had my son do is replace the box and properly plumb it. Ran great for a while then the problems returned. I always figured running it with insufficient vacuum volume all that time had to have implications, so I’ve always said we should be looking there first, but the shops haven’t agreed with me and I’m not there with the truck to look myself.
After all that background, my questions are:
1) could an evap canister just become saturated from running all that time with insufficient vacuum? What would be the symptoms?
2) could it ever get bad enough to throw the codss above? I’m particularly interested in the TPS codes - I assume the TPS is measuring the rotation of the throttle body against some expected value - does it use A:F in some way in that calculation?
3) also guessing there’s a valve on top of the canister that could be shot? How would I test it? Looking through the manuals I’m not finding it, so maybe it’s all just passive, with constant vac?
4) anything else that might cause TPS and rich mixture faults with a brand new throttle position sensor and complete throttle body that none of us are thinking of?
Sorry for all the questions - it’s stumped me and now three different shops, but with the supercharger and that piggy back controller, a whole other can of worms, we really need someone who knows these engines inside and out. Appreciate any thoughts or questions as we sort this out!
I’ve been saying all along I think it’s actually an EVAP system issue, but I’m an old American V8 hotrod guy who doesn’t really understand that system at all!
. Here are my naive thoughts though, tell me if it makes any sense: When I did the supercharger build I accidentally broke the ear/inlet port off the air box where the EVAP vac connects, and temporarily ran a smaller line to a smaller, unused inlet on the box with plans to fix it later. Then I got caught up doing other things, quit driving the truck, and forgot about it. So when the problems started the first thing I had my son do is replace the box and properly plumb it. Ran great for a while then the problems returned. I always figured running it with insufficient vacuum volume all that time had to have implications, so I’ve always said we should be looking there first, but the shops haven’t agreed with me and I’m not there with the truck to look myself.After all that background, my questions are:
1) could an evap canister just become saturated from running all that time with insufficient vacuum? What would be the symptoms?
2) could it ever get bad enough to throw the codss above? I’m particularly interested in the TPS codes - I assume the TPS is measuring the rotation of the throttle body against some expected value - does it use A:F in some way in that calculation?
3) also guessing there’s a valve on top of the canister that could be shot? How would I test it? Looking through the manuals I’m not finding it, so maybe it’s all just passive, with constant vac?
4) anything else that might cause TPS and rich mixture faults with a brand new throttle position sensor and complete throttle body that none of us are thinking of?
Sorry for all the questions - it’s stumped me and now three different shops, but with the supercharger and that piggy back controller, a whole other can of worms, we really need someone who knows these engines inside and out. Appreciate any thoughts or questions as we sort this out!
