Shooting Code 31
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Senior User
Joined: Jun 2006
Posts: 309
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From: Toasty FLORIDA
Shooting Code 31
Hey guys good night!
My 1988 F-250 5.0L mazda 5 speed has been giving me a go around...
It has been giving me the code 31 with a steady light while driving, with the exception when I need to get on the gas to pass someone the light goes out while the engine has a heavy load, already checked for vaccums leaks with a quick starting fluid. The truck also has a rough time keeping idle when it's cold, it keeps shutting off!
Code on the book says it is EGR related any clue????
My 1988 F-250 5.0L mazda 5 speed has been giving me a go around...
It has been giving me the code 31 with a steady light while driving, with the exception when I need to get on the gas to pass someone the light goes out while the engine has a heavy load, already checked for vaccums leaks with a quick starting fluid. The truck also has a rough time keeping idle when it's cold, it keeps shutting off!
Code on the book says it is EGR related any clue????
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
ymeski is correct, Code 31 indicates the EVP signal is below .24VDC. It depends if the code is KOEO or in CM. If it is CM (Continuos Memry) the code means the signal is intermittently below .24VDC. If KOEO (Key On/Engine Off tests) means the voltage is always below 0.24 VDC during the test. The EVP is located on top of the EGR valve. The low signal can be caused by a faulty EVP sensor or a bad EGR valve. The spring on the EGR diaphragm can collapse over a period of time. The diaphragm itself can be torn.
Use a volt meter to measure the feedback signal, if it is low apply a little vacuum with a handheld vacuum pump/gauge to see if the feedback signal raises. If it does not, it's most likely a bad EVP sensor or the EGR valve is not holding a vacuum to pull the pintle off the seat. Use your eyes, ears and test equipment to distinguish the true cause.
My opinion on your vacuum leak test: I have found using starting fluid or carb. cleaner to be a very inconclusive test for finding vacuum leaks on a modern EFI engine. I went through 3 cans of carb. cleaner when trying to track down a high/rough idle problem when I acquired my current '92 F350 w/5.8L engine. I found nothing wrong, but the issues remained. I located my handheld vacuum pump/gauge buried in the tool box, put it to good use testing each vacuum line/circuit. Most of them failed to hold a vacuum. I replaced the faulty lines and porous vacuum reservoirs. Now my truck runs better than it has in years.
Suit yourself, but with the issues you describe I think you have some vacuum leaks too.
Use a volt meter to measure the feedback signal, if it is low apply a little vacuum with a handheld vacuum pump/gauge to see if the feedback signal raises. If it does not, it's most likely a bad EVP sensor or the EGR valve is not holding a vacuum to pull the pintle off the seat. Use your eyes, ears and test equipment to distinguish the true cause.
My opinion on your vacuum leak test: I have found using starting fluid or carb. cleaner to be a very inconclusive test for finding vacuum leaks on a modern EFI engine. I went through 3 cans of carb. cleaner when trying to track down a high/rough idle problem when I acquired my current '92 F350 w/5.8L engine. I found nothing wrong, but the issues remained. I located my handheld vacuum pump/gauge buried in the tool box, put it to good use testing each vacuum line/circuit. Most of them failed to hold a vacuum. I replaced the faulty lines and porous vacuum reservoirs. Now my truck runs better than it has in years.
Suit yourself, but with the issues you describe I think you have some vacuum leaks too.
