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Discussion Starter #1
Lately I've been starting my truck and the rpms will drop real low like its about to die then pick up again. One time it actually did die but restarted fine. I've also noticed a slight lack of power, Not much but a little. I pulled codes and got 334. "Evp sensor closed voltage exceeds highest parameters. I tested the evp sensor resistance and got 3.70K which is good because its supposed to be less than 5K. I got exactly 4.99-5.00 volts for a signal reference with key on engine off. Between signal returm and voltage reference I got .640K. It just says its supposed to be greater than 100. Evp closed voltage is .47 IIRC. It was within parameters though. Now Im curious why the hell I got that code and minor lack of power? Thanks
 

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DKM Mike, mine does exactly what yours is doing. It almost went dead one time but didn't.

I haven't done the checks you have but would be curious to find out what the issue is.
 

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Discussion Starter #3
DKM Mike, mine does exactly what yours is doing. It almost went dead one time but didn't.

I haven't done the checks you have but would be curious to find out what the issue is.
Its confusing because im getting .47 volts closed at idle yet it saus it exceeds the highest parameter which is like .67.
 

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I pulled codes and got 334. "Evp sensor closed voltage exceeds highest parameters.
I had a DTC 334 as well.


I tested the evp sensor resistance and got 3.70K which is good because its supposed to be less than 5K.
EVP Sensor Resistance (< 5000 ohms at pins VREF and EVP)
- 32.6K (My old sensor)
- 4.26K (My new sensor)
- 3.70K (Your sensor is much lower...)



I got exactly 4.99-5.00 volts for a signal reference with key on engine off.
Reference Voltage (5v at pins VREF and SIG RTN)
- 4.78v (My harness)
- 5.00v (Your harness is essentially the same)



Between signal returm and voltage reference??? I got .640K. It just says its supposed to be greater than 100. Evp closed voltage is .47 IIRC. It was within parameters though.
EVP Sensor Resistance (> 100 ohms at pins SIG RTN and EVP)
- 23.1K (My old sensor)
- 126.7 (My new sensor)
- 640 (your sensor is much higher...)




I have found that the resistance readings need to be higher or lower than spec, but not to far or they will again be out of range for the EEC.

See this link: EGR Valve Position (EVP) Sensor Testing & Replacement



Otherwise, I received that same DTC 334 code for a bad TPS. Remember the code is a symptom, not necessarily the actual cause.

See this link: Throttle Position Sensor (TPS) Testing, Replacement and Adjustment



When all is said and done, I have also found that an IAC may actually electrically test good, but may be worn out mechanically.

See this link: How to Test and Clean your Idle Air Controller (IAC)
 

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Discussion Starter #5
Ok its still doing it. It will start up. Rev up to 1500 then quickly drop to somewhere around 4-600 then right nack up to 15. I tested the tps and started with .9 volts all the way to 4.8 volts. The evp tested good as I said earlier and the egr will change the idle whsn I get in there with a screwdriver and move it. The ect has a reference voltage of 4.66 so I don't kmow if thats too low or not. And to top it off, I sprayed vacuum connections with carb cleaner and found no leaks. However the egr control solenoid (I think, its the one with green and white vac lines) Does make a constant buzzing and will buzz for about 5-7 sec after shutdown.
 

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Discussion Starter #7
The venting of the EVR Solenoid is normal. I would still change the EVP, and if it doesn't change anything look closely at your IAC. I do not think your EVP is testing good, as you say. Reread my previous post.
Should I change it with a motorcraft or can I go with another brand? I'd rather go motorcraft but id need to save for that.
 

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What I am saying is that I had similar symptoms, the engine seemed to have less power and would die after the idle dropped after cold startup.

What I found is that even if resistance testing showed </> spec as appropriate, it still needed to be close. My VREF to EVP resistance test on my bad part showed 32.6k which was way above the 5k spec. Using the new Motorcraft part eliminated the problem.


New Motorcraft CX1464 EVP Comparison

• EVP Sensor Resistance (< 5000 ohms at pins VREF and EVP)
New Part Test - 4.26k (4260 ohms)
Your Part Test - 3.70K (3700 ohms)

• EVP Sensor Resistance (> 100 ohms at pins SIG RTN and EVP)
New Part Test - 126.7 (126.7 ohms)
Your Part Test - .640K (640 ohms)
 

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Discussion Starter #9
Motorcraft. What I am saying is that I had similar symptoms, the engine seemed to have less power and would die after the idle dropped after cold startup.

What I found is that even if resistance testing showed </> spec as appropriate, it still needed to be close. My VREF to EVP resistance test on my bad part showed 32.6k which was way above the 5k spec. Using the new Motorcraft part eliminated the problem.


New Motorcraft CX1464 EVP Comparison

• EVP Sensor Resistance (< 5000 ohms at pins VREF and EVP)
New Part Test - 4.26k (4260 ohms)
Your Part Test - 3.70K (3700 ohms)

• EVP Sensor Resistance (> 100 ohms at pins SIG RTN and EVP)
New Part Test - 126.7 (126.7 ohms)
Your Part Test - .640K (640 ohms)
What your describing sounds exactly like what mines doing. Looks like I get to spend $170 on a new one :doh0715:
 

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Discussion Starter #10
Also why is it that bwd costs. 29.99 with limited lifetime warranty and motorcraft costs 135.99 with 2 year. Is it that much better?
 

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...
Ok its still doing it. It will start up. Rev up to 1500 then quickly drop to somewhere around 4-600 then right nack up to 15.
Have you adjusted your throttle plate stop in an attempt to change minimum idle?

Try unplugging the IAC when running to see if the throttle body will hold minimum idle.

I tested the tps and started with .9 volts all the way to 4.8 volts.
Good.

The evp tested good as I said earlier...
Possibly...

...and the egr will change the idle whsn I get in there with a screwdriver and move it.
Good.

The ect has a reference voltage of 4.66 so I don't kmow if thats too low or not.
Good.

And to top it off, I sprayed vacuum connections with carb cleaner and found no leaks.
You should use a vacuum tester.

However the egr control solenoid (I think, its the one with green and white vac lines) Does make a constant buzzing and will buzz for about 5-7 sec after shutdown.
This is normal for the EVR Solenoid. It does two things, applies vacuum to the EGR and vents EGR vacuum to the atmosphere.

I recommend that you recheck codes and recheck the EVR for resistance accuracy. The .640k has me confused.
 

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Discussion Starter #12
...



I recommend that you recheck codes and recheck the EVR for resistance accuracy. The .640k has me confused.
Your talking about the evp right? If so I'll recheck the resistance when I get home. And I drove my truck today and it has been started 3 times so far with no problems. Also I repulled codes last night and got 111 for both tests. I guess it fixed itself :hump
 

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Discussion Starter #13
Is the vacuum tester just a hand held vacuum pump you can rent at an auto parts store?
 

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Discussion Starter #15
Sorry, yes I meant EVP. If your codes are gone and it is driving good, great! Hand Held Vacuum Tester - one of the best tools that I own.


I'll be sure to pick one up. Thanks :thumbup
 

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Discussion Starter #16
Okay so I just calculated my fuel mileage and it turns out I'm getting about 9.2 on a recently tuned up 351w and I don't drive it hard. Im wondering if something is wrong after all.
I calculated by dividing my odometer which read 71 but I compensated for my incorrect speedometer so I really traveled 66 miles. It took 7.8 gallons??
 

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Discussion Starter #18
Initial thought is vacuum leak or lean/rich fuel mixture.
That was my initial thought as well. Ill pull a vacuum on it and see whats going on. What else would cause an improper fuel mixture?
 

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Discussion Starter #19
I have one more question. How come within all this the act sensor was never mentioned. Could that cause poor fuel economy?
 
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