Intake Manifold Pressure is Constant
07-03-2019, 07:16 PM
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Intake Manifold Pressure is Constant A while ago I posted about a TPS issue. I keep getting P0121 and all voltages are in within spec. I've noticed that the MAP voltage on the signal wire seems stuck at 4.2V and a small .2V or less on the ground, I think its .02 but its been a couple weeks since I tested. When I drive and I log, the Intake Manifold Pressure didn't budge from 12.90835857 PSI once for the whole 15 minutes. So that kind of makes sense. Why.
I ran with this 92mm throttle body and TBSS intake for a few weeks before I did my cam swap with no issues. We did the cam, the lifters, rocker trunnions, push rods, springs, all that stuff. After its all back together now we got this issue.
I've replaced TPS sensors and harness, MAP sensors and harness because the TBSS setup is different than the stock intake, IAC sensors, MAF sensor. I've rerouted the grounds from the back of the cylinder head to the front for a fresh connection. I've cut out the signal wire and ground wire from the MAP sensor all the way to the fuse box because that is the only possible place we could have damaged the harness even though we were extremely careful. I even went back to my stock throttle body and adjusted the set screw a bit on that for the bigger cam. I've replaced the intake manifold gasket. I found a pinched hose on the pressure line from PCV to intake. The driver side exhaust header was missing a bolt and we forgot to torque it, we corrected that. This happens with the tuned computer from black bear and my stock computer.
We've done all these things, can't figure out why we have this electrical issue. Any ideas?
I ran with this 92mm throttle body and TBSS intake for a few weeks before I did my cam swap with no issues. We did the cam, the lifters, rocker trunnions, push rods, springs, all that stuff. After its all back together now we got this issue.
I've replaced TPS sensors and harness, MAP sensors and harness because the TBSS setup is different than the stock intake, IAC sensors, MAF sensor. I've rerouted the grounds from the back of the cylinder head to the front for a fresh connection. I've cut out the signal wire and ground wire from the MAP sensor all the way to the fuse box because that is the only possible place we could have damaged the harness even though we were extremely careful. I even went back to my stock throttle body and adjusted the set screw a bit on that for the bigger cam. I've replaced the intake manifold gasket. I found a pinched hose on the pressure line from PCV to intake. The driver side exhaust header was missing a bolt and we forgot to torque it, we corrected that. This happens with the tuned computer from black bear and my stock computer.
We've done all these things, can't figure out why we have this electrical issue. Any ideas?
Last edited by nicman8775; 07-03-2019 at 07:25 PM.
07-04-2019, 09:48 PM
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Not sure if this will be any help or not, but I just started fooling with a 5.3 with the same symptom. The wires for Signal and Ground were swapped at the connector. Is this a new symptom or has it been like this all along?
Joe
Joe
07-04-2019, 10:03 PM
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It's funny my brother and I have been stumped for months and we just decided to try the stock MAP sensor and harness cause why the hell not, and we started getting readings normal voltage and pressure readings again. Havent test driven it long enough yet to see if the tps codes came back but I definitely have a p0300 random multiple cylinder misfire now. I'm hoping it is just cause I didn't have the MAP in all the way because it's a different diameter.