Check engie light code 51

CORVAIRBOB

MEMBER
1995 CHRYSLER LE BARON
68,000 MILES

Well this question is for the best of the best. Lets just see who can figure this one out?
i posted this once before and no one figured it out, but here it is again with some more information.

i have a 95 lebaron 3.0 automatic. When I drive the car I get the check engine light on at about 3-12 mile range. The code is 51 and that code is the 2 sensor ran lean for more then 8 minutes, or a vacuum leak.

now this is what I have done to try and correct the problem so far.
changed the 02 sensor at least 4 times last one is a mopar from Chrysler
changed the map sensor 2 times
changed the plugs
changed the tps
changed the fuel filter
changed the egr valve
changed all the hoses under the hood
changed injectors
changed the heads had a bad valve
changed all the gaskets and seals on the engine and trans.
changed the coolant temp sensor for the ecu.

also I took off the car and ran a pipe down through it to put a big hoke in the thing, now I know for sure it is not plugged. Someone told me that was the problem. Not!

had the hoses inspected again to make sure they were all good.
tested the fuel pressure while driving the car, it runs at 45-50 psi
tested the vacuum while driving the car, steady at 18"
ran the car with the evap canister plugged at the switch under the hood
ran the car with the egr plugged at the manifold and the base of the egr. Did not try it on the egr diaphragm yet. Forgot that hose.
checked the plug for the 02 sensor and it looked good and also measured the ohm's from each wire at the plug to the ecu to make sure the wire was not broken. And also measured the ohm's of different wires that were the same size and length to make sure I got the same readings. I did.
i did not run the car without the fuel pressure regulator plugged I figured that needed to be connected so the injectors would work properly. And I failed to plug the egr at the diaphragm but later I put a tester on that unit and it held the vacuum for over 2 minutes.
one ting tho was when I pulled the vacuum on that egr diaphragm I heard it snap and then I could see the little rod move back and forth when I put a vacuum on that line. So could a stuck egr diaphragm cause that code 51?

so now lets see if I have forgotten anything and if so tell me what I can test next? If not then can any of the mechanics kindly give me an idea of what might be wrong so I can get the fixed.

thanks for any more help and a repair! Bob p.

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Monday, September 5th, 2011 AT 9:43 PM

25 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

You have done just about everything, but you need to disconnect the fuel pressure regulator to see how that affects the pressure. Also, make sure there is 12 volts to the fuel pump itself. It can drop between 10 and 11 when cranking. That is normal.

Also, check the wiring between the power module and the logic module. Check and clean connections and check wiring for continunity. Also, check wiring from O2 sensor to harness. If the wire is grounded at any point, it will cause a code 51.

You have done a lot of work. Please understand that from here it is a little harder to do it. However, check the things I mentioned. Chances are one of them should help. Also, remove the vacuum hose from the fuel pressure regulator and check to see if there is any evidence of fuel in the vacuum hose. That would indicate a bad regulator.

Let me know what you find.

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Tuesday, September 6th, 2011 AT 2:57 AM

CORVAIRBOB

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Outside of connecting a volt meter to the fuel pump and driving the car I already drove the car with the fuel pressure gage connected and I had 45-50 psi during the test trip I always take to test to see if what I did corrected the problem. That should tell me if I have enough power to the pump? And I did remove the wire to the 02 sensor wires and ohm them all the wires had the same reading. Today I will take the harness completely apart and again look for problems. But tell me where the power and logic modules are if they are different that the ecu on the fender?

(Also, check the wiring between the power module and the logic module. Check and clean connections and check wiring for continunity. Also, check wiring from O2 sensor to harness. If the wire is grounded at any point, it will cause a code 51.)

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Tuesday, September 6th, 2011 AT 11:39 AM

CORVAIRBOB

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OK this what happened today. I disconnected the fuel regulator and plugged the hose to the manifold, and the egr diaphragm and plugged the hose to the switch. Then I connected the vacuum gage and took the car on the test trip. Same thing check engine light came on around the same area. But I did notice the vacuum gage ran lower with the fuel pressure regulator unplugged and driving the car. The vacuum reading was around 16" to 18" all the time I was driving the car. Last time it ran close to 18" the whole test trip.

One thing I have had happen more today. I stated that now and then the engine would shut off when I put it in park after driving the car, today it happened at the gas station and then 2 minutes later in the garage and I was able to repeat that 3 more times setting in the garage while idling the engine. 2 times when putting it into park and 1 time when I went from park into drive all while it idled and the normal idle speed. Could the cel be connected to this problem

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Tuesday, September 6th, 2011 AT 1:07 PM

CORVAIRBOB

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OK now I have the complete wire harness out of the car and I took it all apart. I measured the ohm's on the 02 sensor plug again and I wrote it down this time to give you. Looking at the 02 plug and the clip on the rt side for all numbers. And looking at the gray plug with the clip on the left side for all numbers and the alt. Ground
here is what I got for numbers.
1.) Lower rt on 02 plug to the lower left on gray plug at the ecu.3 ohm's.
2.) Upper rt on 02 plug to second from the bottom on the rt side of the gray plug at the ecu.2 ohm's
3.) Upper left on the 02 plug to the black plug at the ecu
4.) Lower left on the 02 plug to the alt. Ground on the alt.3 ohm's

now this tells me the wires are OK. I took pictures and can send them if you need to see where I made the measurements from

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Tuesday, September 6th, 2011 AT 2:47 PM

CORVAIRBOB

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Tuesday sept 6 11
more tests. This test was with all the plugs plugged in and the ecu un-plugged. I put the meter probe in the following places and these are the readings with the batter removed.
From the 02 sensor plug looking at the end with the clip to the right side. This is the ohm readings I got at the ecu plug.

1.) Lower rt plug to pin 41 .4 ohm's

2.) Upper rt plug to pin 4 .3 ohm's

3.) Upper left plug to pin's 5.3 ohm's
pin 9 5.6 ohm's
pin 11 1.1 ohm's
pin 12 1.0 ohm's
pin 29 1.1 ohm's
pin 30 2.4 ohm's
pin 31 87.4 ohm's
pin 32 10.9 ohm's
pin 33 50.9 ohm's
pin 34 80.9 ohm's
pin 35 43.2 ohm's
pin 51 50.8 ohm's
pin 52 36.7 ohm's
pin 53 50.4 ohm's

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Tuesday, September 6th, 2011 AT 4:32 PM

CORVAIRBOB

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So how long does it take to get an answer? Thanks

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Friday, September 9th, 2011 AT 3:48 AM

CORVAIRBOB

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So I paid for this service now how long does it take. If I don't get an answer I will go to paypal and ask for my money back. Bob p

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Saturday, September 10th, 2011 AT 4:14 PM

JACOBANDNICKOLAS

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I'm sorry that it took so long to get back. (Dealing with health issues). Regardless, I have checked out the info you have provided and everything falls within spec. I believe we are dealing with an intermittent issue that isn't showing up all the time. Based on all the electrical info you gave me, I have to resort back to a vacuum leak issue that is causing the engine to go into a closed loop.

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Saturday, September 10th, 2011 AT 5:03 PM

CORVAIRBOB

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Aside from the tests I have submitted what other tests can I do? Is there any vacuum on the transmission? As I do have the engine quit when I put it into park sometimes. And this shows up every time I take the car out. Most of the time I drive in to the lake I get the code at the same spot. Thanks what other tests can I do. Bp. Is it possible the ecu is bad?

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Saturday, September 10th, 2011 AT 5:17 PM

JACOBANDNICKOLAS

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It is possible that the ECU is bad. I hate to say that because of the expense and not being there makes it very difficult for me to be sure. As far as vacuum to the transmission, no. The only thing, as far as a vacuum leak test, is by using carb cleaner spraying it on and around hoses, intake. To see if it has an affect on the idle speed. Please, if you do that, be careful. It can cause a fire. You seem to be very knowledgeable and have a good grasp on what you are doing, but I have to say that. I wouldn't want anyone to get burnt or lose their vehicle. But that is the best way.

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Saturday, September 10th, 2011 AT 6:28 PM

CORVAIRBOB

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OK I went out and did the propane thing. I don;t have carb cleaner and I have a detailed and painted engine and can't have carb cleaner ruining the paint. Here is what I found nothing. I put a new bottle on the torch and I turned it upside down so I could see the propane coming out of the tip. I put the torch at every fitting and along every hose under the hood. The evap the filters the brake booster egr TB injectors the plenum I even remove a vac plug and put the torch around that just to make sure it would work and it did raise the rpm's I even disconnect the hoses on the brake booster to see if the one going into the heater was not broken and the rpm's raised when I removed those hoses and went back down when I covered them with I finger. So I believe I have covered just about everything. Do you guys have anymore tests for me to run. I have exhausted all my knowledge at this point. Thanks for the help so far.

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Saturday, September 10th, 2011 AT 6:58 PM

JACOBANDNICKOLAS

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I hate to say it, but you have me stumped at this point. Everything shows what it sould be. Maybe we are trying too hard. I can't remember, but you did say that you ran a live scope on the O2 sensor correct?

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Saturday, September 10th, 2011 AT 7:18 PM

CORVAIRBOB

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No but I have replace that 02 sensor 4 times already they all can't be bad. The last one cost me 200.00 from Chrysler. I even put the 02 sensor into an extender to keep it out of the exhaust to see if that would help nope. And I took the cat and remove the biggest share of the guts so it can't be a plugged cat anymore. And yes I cleaned out the loose material so it would not get into the muffler.

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Saturday, September 10th, 2011 AT 7:44 PM

CORVAIRBOB

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Forgot to add when I got the car the cel came on and I called the Chrysler new car dealer I got the car from and they did not even want to look at the car even if I paid them. They told me to take it somewhere else. I did and that dealer did not find anything either. Now maybe they looked and maybe they didn't look? But I have done everything I know and I have a ton of car buddy's and they don't know. Something has to be wrong with it. Do you know a way I can contact Chrysler direct the factory and ask those engineers if they have a clue? Thanks bp.

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Saturday, September 10th, 2011 AT 7:48 PM

JACOBANDNICKOLAS

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I don't have one in front of me, but in any Chrysler owner's manual are contacts for district reps. That is where I would start.

If you can't find one, let me know where you live (you may feel uncomfortable with that) but I can look in one of my owner's manuals.

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Sunday, September 11th, 2011 AT 5:34 AM

CORVAIRBOB

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I sent them an email stating what is wrong and what I did and where I got the car and what that dealer told me when I drove the car home and the light came on 10 minutes from the dealer. I was pressed for time and I should have turned around and made them give me my money back. But I didn't and now I'm starting to regret that. I called them when I got home to bring it back and have them check it out they wanted nothing to do with the repair even if I paid for it. I think I may just get a new computer and if that fails I will park it on the road and sell it. Thanks for your help. Maybe someone reading all of this can shed some light on it. I have worked on cars as a shade tree mechanic for 40 years and I just can't figure it out. I even was a mechanic in the army for 22 years and this has me stumped as far as under the hood goes. I may just send the ecu into the repair center they all seem to be in Europe and see if they can find any problems with the ecu. Look at the engine it was this clean even when I got it. Show room new. Every hose on the car was new. And all the sensors had repair stickers on them. I know because when I started getting parts they had the same stickers on them. That tells me now they change all these trying to find the problem. Anyone else reading this is more than welcome to send me a note with suggestions HELP!

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Sunday, September 11th, 2011 AT 2:05 PM

JACOBANDNICKOLAS

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Wow! It does look new. I purchased one in 1988 new. That is when convertables were just getting popular again. I sold it 10 years later with 4K miles on it (needed money to purchase property). It was the same color, but the V6 wasn't available yet, so it had the 2.5 and I ordered it with a 5 speed. I loved the car. Never drove it in snow or rain. I wish I still had it, but wouldn't want to be going through this type of issue.

I knew you had a lot of experience working on cars. Now that I read your last post, I understand why. Keep me posted. I would love to know what is causing the problem.

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Sunday, September 11th, 2011 AT 4:21 PM

CORVAIRBOB

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Well Jacob or nick. Today I went out to start the car and move it to the road and it would not stay running unless I held down the throttle. Then it would idle. I tried this a number of times and it did it every time. Then as I just about gave up and was ready to call the scrap yard to take it away it started and would idle. I did have a dead battery from leaving the lights on over night and had to recharge the battery. So it may have just forgot it;s program. I'm getting real sick i=of these problems on this lemon car. What do you think now? I will try it again after it gets cold and if it fails to keep running then I have a complete set of new problems. The last thing I was doing was testing with propane while it was idling outside of that dead battery. Thanks bob p.

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Sunday, September 11th, 2011 AT 5:02 PM

JACOBANDNICKOLAS

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Wow. If the battery was completely dead, the computer may have to go through a relearn. But if you had to keep it to the floor, it sounds like it is flooding, and you're right, that is an all new bunch of possible issues. By the way, I'm Joe. Jake and Nick are my kids. I used their names so I wouldn't forget my user name.

I'll be up late tonight. Let me know if it changes.

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Sunday, September 11th, 2011 AT 5:18 PM

CORVAIRBOB

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Well I tried later and it started and ran so my guess is the ecu was without power long enough to forget it's parameters. After it warmed up it did OK. Tomorrow I will take it out for a test drive again and see if the code 51 returns. My guess is it will. This week I will disassemble the top end to the intake and see if the gaskets have been compromised and also check the TB and vacuum piping under the intake plenum. If all that turns out to be fine then it is the computer not processing the 02 sensor signal and then making the car run in the limp mode. I will keep my progress posted as a learning tool for now. Thanks bob p.

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Monday, September 12th, 2011 AT 1:08 AM