Chevrolet Corvette:

EVAP issue/ MAF

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#1 1/26/2012 2:01 PM

Rags
New member
Registered: 1/26/2012
Posts: 6

EVAP issue/ MAF

I have been chasing this problem for months>
P code 0100 and 1441 Maf sensor and open purg.
MAF has been replased twice including screen, both solinoids on evap systen on eng have been replaced but both are open always.
Canister and solinoid at rear have been replaced
On examination MAF is geting 5 volts and with eng running both solinoids are getting 12 volts, hoses are routed correctley and not blocked.
I believe that both solinoids (evap) should be closed with ignition and eng off.
Any assistance would be helpfull

1996 corvette
LT4
99,000 miles
stick shift

Last edited by Rags (1/26/2012 2:03 PM)

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#2 1/26/2012 9:42 PM

TechHelp2
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Registered: 11/23/2009
Posts: 1039

Re: EVAP issue/ MAF

Between ground G106 and the ground at the mass air flow sensor there is a splice S119, it appears the purge valves and the mass air flow sensor share this ground. Check the ground on the sensors going to the ground distribution cell 14. I listed the schmatic below.

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There are many other components related to these codes that need to also be monitored by a scanner that can contribute to these codes. You would also need to check the ground wires from the purge valves to the PCM to see if the wires to and from the PCM are not open or grounded.

Loss of EVAP pressure from a hose that is cracked can cause a pressure lose when the system tests itself causing a faulty condition and setting a check engine light.

They have a fog machine that injects a fog into the EVAP system and you would look for the smoke coming from a broken hose that would show where the leak is. It could be as simple as a leaking gas cap causing the loss of pressure. The pressure could be fine and have a faulty sensor in the system. This would show up on a scanner.

Look into the common ground first and get back to us with your results, we can go on from there.


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#3 1/29/2012 1:27 PM

Rags
New member
Registered: 1/26/2012
Posts: 6

Re: EVAP issue/ MAF

Thank you for your help I have spent some time attempting to follow your instructions locating and inspecting the G106 was almost impossible I removed the side panel battery and battery shelf and only with a 4ft extension was I able to reach the G106 it was tight and clean and wasn’t wanting to move tightening or undoing I thought it best to leave alone. Because of the continuity between EVAP purge switch (the round one) black to black on MAF or either one to engine block ground. I could not locate S119 even though the FM said it was 8 MM from G106 just too cramped either from on top or from the bottom. I did not know how to locate the wire from the EVAP vacuum control solenoid (Square one) one pink one green with white stripe to the CPM I did not know what terminal to look at on cpm.
Also I didn’t understand the box on the wiring diagram “Ground Distribution Cell 14   is there such a thing? I found no mention of that cell in manual.
While in the area I did remove and clean and sand G101 and G102, G107 was accessible but also clean and the ground strap from it goes to G102.
Noted all three units have their own continuity grounds and with eng on they all have 12 volts
Sorry I hope this information was helpful.

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#4 1/29/2012 8:01 PM

TechHelp2
Administrator
Registered: 11/23/2009
Posts: 1039

Re: EVAP issue/ MAF

To me it still sounds like a ground issue. If you have voltage then it has to be a ground related issue.

I would check the continuity of the ground wires from each device to the PCM to see if there is no break or resistance in the ground wire(s) to each device.

It could also be the PCM not being able to supply or switch the ground which would mean a bad PCM.

In the dealer ship they have a very complicated scanner where they can turn the signal on and off for diagnosis purposes. When they command the EVAP solenoids to turn on and off they can come up with a positive diagnosis.

With this problem being as complicated as the one you're having you may not have a choice. You have done a good job so far, sometimes technology puts some problems out of our hands and into the hands of the professionals.


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#5 1/30/2012 6:59 PM

Rags
New member
Registered: 1/26/2012
Posts: 6

Re: EVAP issue/ MAF

The problem, how, do I check the ground to PCM where are they located what port or group of wires going into the PCM eg red/blue/gre etc and number? I can’t find that, in the service manual.

Today I did some more checking I had another solenoid that I had (I hit with 12 v it went click on another engine bat) and is sort of closed but didn’t reopen, I installed it on the eng and there was no vacuum on the intake with motor running so went back to the original and there is vacuum there and before the purge round solenoid with engine running.

I can’t afford to take the car to a garage to have it computer tested for now. I only have my scanner and that codes only. I have vacuum gauge and test meters. I left the vacuum gauge on all day to see if it pressures + or – in the sun but really didn’t see and change so not sure about the tank. Maybe I’m getting over complicated with this the voltage into each unit is it a variable or it is freq variable. I guess if you can direct me to the PCM grounds that will be next
Thank you
In the past I have replaced the computer and distributor as well as coil and plugs.

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#6 1/30/2012 9:53 PM

TechHelp2
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Registered: 11/23/2009
Posts: 1039

Re: EVAP issue/ MAF

On the PCM there should be three plugs. On Plug C1 check the black and white wires in slots 2 and 18.

On plug C3 check the wire is slot 32.

On plug C4 check wire slot 1. All of the wires are black and white.

Get a good ground at the battery and check these wires for resistance, they should be 0.

Check all the grounds this way. There are other ways to check these wires but a professional quality scanner is needed. As I explained before the mechanic can use the scanner to turn these devices on and also monitor their activity to help locate the problem. It can also be the PCM not supplying the ground internally.

Most sensors have a 12V wire, a ground wire and a 5V reference line. Make sure you have the 5V going back to the PCM. Again this can be checked with a professional quality scanner.

If you don't find the problem with what I gave you in schematics you may not have a choice but to bring the car in to the dealer.

Try these suggestions and let me know how you made out. 

You can get all of these wire schematics at the Alldata automotive information website at ALLDATAdiy.com. For a small fee you can get all the information on the car for a full year including service bulletins and recalls. 

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#7 2/5/2012 3:38 PM

Rags
New member
Registered: 1/26/2012
Posts: 6

Re: EVAP issue/ MAF

I can definitely check the grounds to the PCM your description was i believe for the wrong model my pcm has four main terminals coded with colors red, grey, blue and black where are the grounds?
I’ve been bust and haven’t had a chance to do anything sorry for the late response
Thank you

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#8 2/5/2012 9:14 PM

TechHelp2
Administrator
Registered: 11/23/2009
Posts: 1039

Re: EVAP issue/ MAF

The black plug is not in the circuit of this problem. If you want to check the grounds check the black and yellow wires or any black wires in the plug.

I also said the grounding problem could also be inside the PCM. That's why you would need to take the car to the dealer and at least pay for the diagnostic time to fix the problem.

If it is the PCM you would need to still have to have the PCM reprogrammed. You would need a professional scanner to do this procedure.


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