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Unread 04-02-2013, 08:13 PM   #1
JBentley
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1988 YJ Wrangler 
 
Join Date: Jun 2009
Location: Mich/Va
Posts: 16
No 5V to MAP sensor

88 YJ 4-banger

I've been trying to find the cause of my crappy running issue and I don't seem to be getting the 4.5-5V to the "B" terminal of the MAP sensor. I do not get the volts at the wire harness connector to the cpu either. The harness is plugged in and the ign is in the ON position. I do get good continuity through the wire from cpu to connector.

Is there any way to jump/feed this 5v/check to make sure this is my running issue?
Is there anything I'm missing?
Is the fix to replace the wire harness/connector? Even though I'm getting good continuity? I'm not to sure how the power is fed to/through the harness connector.

Any help is greatly appreciated.

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Unread 04-03-2013, 09:57 AM   #2
Que89YJ
Web Wheeler
1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,699
You 5v supply is common with the TPS. Check for the 5V on the TPS. Your 5vdc should be on pin C and B is your signal to the ecu and A is your ground. Go to page 728 of the FSM and you can see what I am saying.

87
http://dl.dropbox.com/u/40590346/87-...M%20manual.pdf

What is going on with your Jeep?
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Unread 04-03-2013, 11:08 AM   #3
JBentley
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1988 YJ Wrangler 
 
Join Date: Jun 2009
Location: Mich/Va
Posts: 16
TPS is the throttle position? I will recheck but I know I had voltage the last time I checked. Does that mean it feeds off the purple wire that runs to the B of the connector? If so I do not have a splice. I do get voltage to the C port of both the connector and cpu harness and I do get good continuity and ground on the A terminal.

Of the various problems worked through already, it still runs very rich. You can tell its not running in harmony with itself. The only way I can get it to run without heavily surging is unplugging the vacuum source from the map sensor and plugging that hose and or introducing a large vacuum leak to compensate for the rich mixture.
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Unread 04-03-2013, 12:43 PM   #4
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,699
Did you do all the sensor adjustments? The TPS, IAC, wot switch, and fuel pressure all have adjustments. Do the adjustments before doing anything else. The measurements will tell you if anything is wrong. I posted the link to the FSM along with the page to look on for the voltages and basic wiring diagram.

Running rich is usually 2 things. Fuel regulation when cold is controlled by the ecu using the temp sensor input and a default calibration. When it warms up it starts using the O2 sensor for regualting the fuel. Check both sensors, the FSM I posted will tell you the measurements. The other usual issue is the exhaust manifold cracks which allows air into the exhaust. That tells the O2 sensor that itis running lean and the ECU will dump fuel. Look around the exhaust manifold for any loose bolts on it and check the manifold for any cracks especially around the collector tubes. Also you have an egr. I might suggest capping it off if your state does not have an emissions test. It will cause exhaust and intake leaks and can cause issues if the valve fails open.
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Unread 04-03-2013, 02:51 PM   #5
JBentley
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1988 YJ Wrangler 
 
Join Date: Jun 2009
Location: Mich/Va
Posts: 16
Yes I've adjusted all the sensors. Most if not all are new. My original fuel regulator did not have adjustment nor did the new one. I am getting 14psi or whatever it spec'd in the Chiltons manual I have. I will also check the FSM you have posted.
I've been all over this thing and I am quite certain it's either in the harness or the CPU itself. I've changed both temp sensors and the o2 sensors. Both read within specs according to the manual. There's a new egr valve on it but the old one was completely seized so I know that's not a variable. All new vacuum hoses and checked for leaks many times. Did compression and leak down tests although the motor itself only has 5000 miles if that on it.
I haven't changed to the 190* thermostat as someone suggested to put the computer into the "non warm up" mode but I am pretty certain this is not the cause. I can get the coolant temp up high enough where it should be out of the warm up stage. Not certain though.
All the ignition components have been changed as well as the crank sensor. The plugs consistently read rich and as I said there's a major bog.
The only things that haven't been changed are the CPU, harness, and wot sensor (which has power and is adjusted to spec). The exhaust isn't clogged and there's not an obstruction in the intake manifold.
My idle control sensor is new but it does not activate or constantly operate the plunger when it goes into its erratic idle so I'm not sure of that things fried too.

I think that's all I know. I took the entire jeep apart and put it back together quicker then I've been able to get it running properly. It was running poorly before I took the helm and have lost a lot of interest. Good luck! I hope something rings a bell.
Thanks again
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Unread 04-03-2013, 04:39 PM   #6
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,699
I typed a huge thread and lost it! Grrr

Look at this thread for adjusting fuel pressure. Do the pressure test again and see if you are losing pressure when you shut it off. Shaef had a bad injector and rebuilt his throttlebody because of it:
http://www.jeepforum.com/forum/f12/2...10/index3.html

You must have a thermostat that reaches operating temp of at least 185. You can check it by measuring the coolant temperature in the radiator. It will be about 10 degrees lower then the engine coolant so use a meat thermometer and check for a temp of at least 175.

The O2 sensor reads between .1 and 1vdc during normal operation. The lean condition would give you a consistent reading below .4. The thing I mentioned was checking for any exhaust leak. The manifold bolts are notorious for loosening and it is very common for the exhaust manifold cracking especially around the collector tubes. It is one of the most common reasons for a rich condition.

I am surprised you figured out how to move the ISA to adjust it. An old timer told me about moving it to set the TPS or I never would have figured out the trick with a 9v battery. If you did the adjustment the ISA must be moving in both directions.

I see your post says Mich. Where are you from?
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Unread 04-04-2013, 11:52 AM   #7
JBentley
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1988 YJ Wrangler 
 
Join Date: Jun 2009
Location: Mich/Va
Posts: 16
I will check the thread. My regulator is leaded in at the bottom so I don't have the adjustment capability. I can recheck the fuel pressure but I am pretty sure it holds the pressure while its off. I had the gauge hooked up to it while testing something and I never remember it dropping. I've been wondering about the injector. That, along with the 3 other things, hasn't been changed. I did change all the gaskets, O rings, and cleaned up the throttle body but didn't change the injector.
Can I back up for a second. Why do you think it's not the signal on that B terminal that's causing my problem? Since the only way the engine changes is when you mess with the map sensor. I hold good solid vacuum, about 14.5-15 constantly without fluctuation so that should eliminate a vacuum leak right? Wouldn't it be showing up even if it was minor?
I checked the tstat neck with a temp gun and I know it was 190+ but I had to work it to get it that high. I'm going to swap in the 190 stat this weekend.
I will check the O2 with that info. I think the Chiltons had me measure the ohms? Between the wires. It was in spec but I hate those vague measurements.
I did not check the manifold for cracks but I did take them both off because I wanted to check for blockages and leaks so I think along with holding solid vacuum that might not be my issue? I've used propane around the manifolds and such and never had a surge but I'm slightly Leary of that test since the motor is not really in a state of knowing what it's doing anyways.
I may have led you in the wrong direction. I don't think I used the trick with the 9v battery but I did change out that entire module. I adjusted the wot sensor where you have to get it within the certain voltage.
I hope I don't come across and wanting to argue with you that's not my intention. I'm just trying to make sure you know what I know because you clearly know what your doing. But I have been up and down this thing with whatever I knew how to do. You've got me excited now though, I'm ready to finally kill this problem.
I'm right around Detroit but I'm splitting my time in Virginia bc of work.
Let me throw one more thing your way. Back before I changed nearly everything, one of the first things I changed was that idle something control. Whatever the unit is that directly contacts your throttle linkage. When I hooked that up for the first time the thing purred like a kitten. Like an idiot I turned it off after a couple minutes without checking anything. When I restarted it went right back to surging. If I remember correctly, during that time of running correctly the O2 sensor wasn't connected and one of the temp sensors. It does the surging whenever everything is hooked up correctly. You can stop it by disconnecting the vacuum source to the map and actually drive it without hard acceleration. Cold weather or introducing a vacuum leak improves it a little more but the plugs run lean and obviously that's just a bandaid.
Thanks
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Unread 04-04-2013, 02:15 PM   #8
Que89YJ
Web Wheeler
1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,699
Where are you at around Detroit. I am in Trenton. If the Jeep is around here and you are close by I can come over and we can try and figure this out together. I will go through what you posted when I get home and think it through. We will get it figured out. I have an 89 and we can use my ecu to check your seup.
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Unread 04-05-2013, 02:53 PM   #9
JBentley
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1988 YJ Wrangler 
 
Join Date: Jun 2009
Location: Mich/Va
Posts: 16
I'm from st Clair shores. Unfortunately, I brought the jeep down to Va to give me something to do and now I can't get it back because of the way it's running. I need to reach out to someone around here to test ecu's.
I can consolidate everything into one post of everything I've done and know. Recheck things like the fuel pressure or things I've forgot so you have everything in one plae.
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Unread 04-05-2013, 03:19 PM   #10
Que89YJ
Web Wheeler
1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,699
pm sent call me
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