2005 Saturn ion MAP reads backwards

A bad sensor can’t cause bad readings with other sensors. I’m guessing you’ve installed aftermarket parts. They would be my prime suspects. Same thing if they’re parts that don’t ‘belong’ there from a different engine. They may work differently than the stock parts and require ECU remapping to work correctly.

More info on performance issues here.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

Good luck and keep us posted.

[quote=”Clayhawk75″ post=139674]Hey all,
So, my girlfriend has a 05 Saturn ion 2.2 with 2.4 intake manny and TB swapped, and breather filter as opposed to the engine to air cleaner connection. All was well, she loved it, car was FAST I was happy. Until it started throwing itself into safe mode when you accelerate hard. I replaced the MAF and MAP sensors, no change. So, today I went and bought a scan tool that viewed live data. Well, on the test drive the MAF was wayyyy low, like 1 or 2, and the MAP was reading backwards, 4-5 PSI at idle and 11-12 when driving. So, my first question is: could the IAT be faulty and screwing with the MAF? Like, if intake air is actually colder/warmer than it reads and so the MAF is being incorrectly heated by the PCM?
And my second question is: Why does the MAP read backwards?
I’m seriously trying to avoid replacing the APP sensor, but if the MAF and MAP both check good, I’ll start tinkering with replacing it.
Thanks for your help
Clay[/quote]

MAP readings are not what the vacuum of the engine is… MAP readings are calculated as = 29.6 inches of mercury (or current barometric pressure) minus (-) the current vacuum of the engine. So get your barometric pressure where you live (if you live in higher altitudes it may be a lower number) See link…

http://water.me.vccs.edu/courses/CIV240/table4.htm

So find your altitude, hook up a vacuum gauge to your engine (I.E. it reads 22 inches of mercury from your idling engine and your altitude is say 2000 ft. above sea level (27.7 inches of mercury) then the MAP sensor should read around 5.

When you accelerate the engine and the vacuum on the gauge drops to say 17, then your MAP number should be close to 10.

Cheers

-Karl

[quote=”Clayhawk75″ post=139708]So, am I just overthinking it or is there actually a problem with the MAP? Because it should go down on acceleration and up at idle, but it’s doing the opposite.[/quote]
Barometric pressure is more or less FIXED (it varies daily but not by much as long as the altitude is the same). When you open the throttle, the manifold vacuum DECREASES.

So, for example, where I live, the baro is around 28 inches. If my engine vacuum at idle is 22 inches, my MAP should read the DIFFERENCE, which is 6 inches (28 minus 22). When I hit the throttle, the vacuum goes down, to say, 10 inches. The MAP will now read baro minus 10, which is 18. So, when you rev the engine, the MAP reading should go UP, and then on deceleration or idle it should go DOWN, and that is pretty much exactly what yours is doing.

The MAF should read fairly low at idle, because the air demands by the engine are low. As you accelerate, the air demands increase, so the MAF should rise. When you decelerate, the throttle closes, and the air demands are once again low, so the MAF reading should fall. To test the MAF, get your baseline reading by watching the MAF on the scan tool and snap the throttle a few times, looking each time at the low number where it settles (they should all be very close), then average the low numbers together. Now, slowly open the throttle while watching the MAF data. The MAF readings should slowly and smoothly rise with the position of the throttle. Get it up to like 2500-3000 RPM and then let the throttle snap closed. The MAF should abruptly (but still smoothly) fall back to around your baseline average. If the sensor readings are not smooth and/or jump around, or you cannot get relatively low numbers for the baseline average, the sensor is faulty. Yes, I have seen new MAFs come right out of the box faulty, especially when they are an aftermarket brand. Also, MAFs can be faulty without setting a check engine light code.

Since you changed the throttle body, the reason it is probably going into limp mode is because the throttle position sensor data is going out of range. You probably just need to have the computer re-learn the TPS.

[quote=”Clayhawk75″ post=139764]Any ideas on relearn procedure for the TPS?[/quote]

From the FSM:
Throttle Body Relearn Procedure

The engine control module (ECM) stores values that include the lowest possible throttle position (TP) sensor positions–0 percent, the rest positions–7 percent, and the return rate of both springs. These values will only be erased or overwritten if the ECM is reprogrammed or if a throttle body relearn procedure is performed. Observe, if the battery is disconnected, the ECM will immediately perform a throttle body relearn procedure when the ignition is turned ON.

A throttle body relearn procedure is performed anytime the ignition is turned ON, with the engine OFF for longer than 29 seconds. After 29 seconds, the ECM commands the throttle plate from the rest position to full closed, then to around 10 percent open. This procedure takes about 6-8 seconds. If any faults occur in the throttle actuator control (TAC) system, a DTC sets. At the start of this procedure, the scan tool TAC Learn Counter parameter should display 0, then count up to 11 after the procedure is completed. If the counter did not start at 0, or if the counter did not end at 11, a fault has occurred and a DTC should set.

[quote=”Clayhawk75″ post=139969]Awesome thank ya!
Also, I did the MAF test you described, at idle it reads .01 lb/s and after revving it and watching it fall it always ends at .01, got it up to 3k, snapped the throttle and it fell almost immediately back to .01, with very little transition. Does that sound right or could I have a MAF problem?[/quote]
That part of the process sounds good. Did you watch the voltage climb as you slowly raised the throttle? Was the voltage transition upward smooth? If so, the MAF is fine.

Cool. Hope it all works out.