when checking the map sensor on my 1990 corolla i got a 5.02 volt reading between the E2 and VCC on the connector. when I checked the voltage between the PIM connector and theE2 connector it was 3.66 volt. isn't that a large drop across the sensor? the largest volt drop I have with vacuum is 1.96 volts are these reading good or bad
engine started to stall and hard to start changed fuel filter, pump to no avail.(listening to the little voice in my bedroom)checked for codes threw a 31. Have started looking at the map sensor
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Your VCC is good 5V is normal Key on engine off is good too. 3.6 to 3.9 is normal. As vacuum is applied the voltage should drop slowly. 20 inches. is about 1.9 to 2.1 volts. This is basically idle 19 to 21 inches of vacuum.
Then whats the 31 code about? Vacuum circuit appears ok but its hard to start and really stumble and dies. my very first thought was the IAC so I cleaned the throttle body (inplace) with a spray cleaner and to no avail. the IAC appears to be part of the throttle body. Where to I go from here?
DOES THE CODE 31 COME BACK EVERY TIME AFTER YOU DRIVE IT AND THE CODE WAS CLEARED PREVIOUS TO DRIVING?
I cleared the code by disconnecting the neg batt cable. this makes it easier to start. still hard starting. getting it to move is the problem. I can get it past idle by easing down on the throttle. turning on any assessories is dicey although the up idle circuit does appear to work sorta. and yes the code comes right back.
Can you monitor the PIM voltage while doing this or driving to see what it is doing? Did you check the vacuum line very close of cracks. Did you check the pin fit of the 3 female pins in the connector?
the connectors appear good I cchecked the pim voltage at the connector by piercing the pim wire used the vacuum line in to check the voltage drop it holds vacuum. checked the pim voltage while running. wife worked the throttle recall voltage variation but don't remember. what it was. Voltage seemed to be all over the place. at about 3000 rpms.
Do you have a graphing volt meter or access to a scope to monitor this voltage fluctuations at 3,000? What do you mean by all over the place? Numbers please while holding it steady at 3,000.
ok just have a digital vom. wife and I will figure it out after work. then send you the info.
Ok after clearing the code and several minutes of trying to start the car finally came to life. It always smells like raw gas when doing this.
Here are the readings.
Idle 1.66 v
1500 rpm 1.46v
2000 rpm 1.47 v
2500 rpm 1.49 v
3000 rpm 1.52 v
After the car starts the car dies with normal throttle tip in
you must ease the rpms up
Those numbers all look good and basically reflect 19 or 20 inches of vacuum at each of those RPM settings. The only way that you can get the code 31 set is if the PIM signal from the sensor is not getting to the engine control computer. It Is possible that you have a break in the wire or short in the wire between where your checking at the sensor and the engine control computer. The only way to know for sure is to check for voltage at the engine control computer or ohm testing this signal wire from the sensor connector to the connector at the engine control computer. There is a remote chance that there is something going on inside the map sensor causing an issue. The only way to know for sure without doing a bunch of diagnostic tests is to purchase another map sensor or by one that the junkyard and just try it.
we basically parked the car friday night running fine and when my wife started it Saturday morning and started to work it started not working. I noticed a little studder when going up a long grade at 45to50 mph and the gas mileage has started to suffer but hey I'm in Arizona we live by A/C here. what are the odds. And why would I have the same settings at those different rpm settings? Doesn't he vacuum drop the more open the throttle is open. I've Vacuum gauges on cars before and I"ve actually owned cars with vacuum motors. at open throttle those wipers would realy slow down. I have already ordered a used MAP. Any other suggestions?
This code 31 is strictly an open or short circuit in the signal wire to the engine control computer. This is not vacuum related. Your assessment on the vacuum situation is correct. Vacuum does go to zero on wide-open throttle. This is only momentary until the throttle starts to close. When you have the throttle set at the RPM settings that you have when you initially make the step to the next higher RPM if you notice your voltmeter very closely the voltage will rise for a split second then will stabilize back to the setting that you have as far as the voltage goes because your vacuum then regains back to about 19 or 20 inches of vacuum. There will come a point near wide-open throttle that you're voltage will rise back up but you never gonna see that before you blow the engine up because you have no load on the engine. Let me know how it goes.
ok I'll let you know wthat the different MAP sensor will do
So I haven't put in the other Map yet. I ordered it via ebay and I guess its coming by snail mail. In a word you have been most helpful, however I didn't want to, and I thought you agreed to, wait until the MAP was installed. I removed the throttle body and cleaned it, reinstalled and while it was hard to start it seemed to help a lot. I decided to recheck the values. and they were rock solid at 1.97 the tip in throttle was better and I did actually see the voltages change when I changed the throttle at 1.66 goup to 1.81 and back down then all of a sudden it went to 2.81 volts started missing and finally died. Back to a code 31 and allbut impossible to start . Guess I'll wait fot the map to show up and go from there. Do you want to continue the thread or wait for the outcome or are you through?
Waiting is just fine just don't forget me.
so the map relay made no difference. cleaned the throttle body and when it starts its smoother. I noticed the when the engine starts the Check engine light goes off. a friend said he had problems with the fuel injector relay? and normally the check engine light is off. I've been playing with the cold start time delay switch and after the no start problem with the new MAP I disconnected that switch and she bumped and She bumped and started ran smooth ( have some studder at low er rpms have the idle up) I turned on the AC and let it warm up the cooling fans came on she shuddered and died. CEL came on checked code 31. Cleared code started up just okay no CEL I noticed that the fuel injector relay felt very warm. these circuits relays switches are all work in concert with each other when they are on is when I start having problems. she shudders backfires and dies then I get the 31 code. Heads spinning Any thoughts?
Have you ever checked the voltage at the PIM input at the computer? I have to again repeat that the only way you can get a code 31 set in the engine control computer is if this PIM voltage input to the engine control computer is shorted to ground or is going open.
in a word no. but I will
Let me know what happens to the voltage at the computer and ohm test the line from the sensor to the computer.
Ok I checked the voltage at the PIM and E2 and got 3.66 V I pulled the connector and ohmed the wiring they ohmed out fine. No open no short. I started with the basics. Checked the ignition system the plugs were worn and 3 of 4 were not seated. Cables fine capand rotor fine. Coil speced high. changed the plugs and coil. started like my old car. Went and got gas and it stalled at the corner. started and got gas, with additive, started fin. Drove around started missing stalling, but always starting. got home. Next i looked at fuel delivery Ohmed injectors they were fine. Already changed the fuel pump and filter. When I start up cold it starts right up (open Loop) As it warms up it start to studder then miss then won't hold idle etc. Dirty injectors? Any suggestions? I know that today as I was trying to get the injector to unclog by running it it warmed up I turned the ac on Stumbles. It at one point died and started running backwards Smoke out of the air box. It coded 31. I cleared and started. turned it off and rechecked the MAP completely over Same Values no wiring shorts or opens. When I check the PIM voltage I am checking it at the E2 and PIM is that correct? If my wiring diagramis correct it traces toE21 at the ECU. It also conects to the TPS and coolant sensor the air intake sensor. the brown wire appears to be a ground. Any suggestions?
The PIM input to the engine control computer is the light green wire with a red tracer in connector T3 and is pin number 4 as seen from the face of the connector as it is unplugged and you're looking at it. See the image below for clarification. With the connectors all plugged in and you carefully back probe this light green wire with a red tracer and the problem occurs setting the check engine light on what is the voltage doing on this wire? The Brown wires are in fact ground wires but I would prefer that you have your ground probe from your voltmeter to a good metal brace under the instrument panel. If you wiggle the wire into these connectors at the computer can you make the problem occur?
Sure. but I just started it and it fired right away but you can feel the miss. It closed loop and started to really act up it died. Started and kept running with throttle then shut it off no code.
We need to monitor this voltage when it acts up and then set the code. Let me know how goes.
ok It was hard. But I finally got it to run and the only time the voltage changed was when it started to miss. No code, I ran the idle up to a1000 and could run the ac lights etc with just a little occasional miss. while idling the Map read 1.36v when the ac cycled (idle up works) I got 1.66V. AC off and the cooling fan cycles on 1.76v. No code. when it misses the voltage goes up to 2.21v and back down to 1.36V when it catches up. Again no code. I drove it around the block. some bucking missing unless I ease into the throttle at 2000rpm. Above 3000 and it acts quite well.
The slight voltage rise would be due to the cylinder misfire more than likely. I'm about out of options on this one until you can confirm what the map sensor voltage is doing when the code sets. It is difficult to say for sure what's going on here. This probably is going to be a hands-on repair. There are certain limitations I have to work with in this type of format.
Ok some way some how the code sets from an extenuating circumstance. A back fire or the an open in the ground brown wire. eo2 or eq2 eo1 o2 sensor all terminate to a ground some where. I'm still chasing the miss and suspect the injectors. If I can eliminate the miss and studder and I think its in the air fuel ratio circuit a poorly operating o2 sensor something. all will be well thank you for your time you have been most helpful.
You are welcome. The O2 sensor should not be causing this.
The o2 sensor was in reference to the commonality to the ground circuit. I believe its an injector or the injector circuit that's causing the miss. I wait for the opportunity to rate your help. Thanks again.
You are welcome. Injectors rarely fail on this engine. And when they do they normally do not come back.
ok. I call do overs. Setting aside the map code, I have a corolla that starts fine cold but as it warms up I have a slight miss. I have turned up the idle to improve drivability to about 1000rpms. Pulls fine in first, second gear the car bucks and misses below 2000rpms and easing into the throttle seems to help. same for third and fourth.
I have replaced the fuel filter and pump, replaced the map sensor, air filter, throughly cleaned the throttle body, replaced the spark plugs and coil. Do you have any suggestions?
Unfortunately I don't have any other information that would be able to assist you further. Throttle position sensor is about the only other thing that you could test or check but normally that will always set a code when it malfunctions. My recommendation at this point would be to relist a new question with the information you just posted. However any other expert would need to know about the code 31 because there's no way this can set unless there is a malfunction in the computer or something going to the computer. The manifold absolute pressure sensor is the primary load indicator on the engine to determine fuel injection duration. The only accurate way to check that is with an oscilloscope. Try to disconnect the throttle position sensor and see what happens when the drive the vehicle as far as acceleration. Again I opted out because I'm out of options and I would need to physically work on this car in order to solve the problem. No need to reply back to this post.
Toyota Master Diagnostic