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MAPseems bad but no OBD2 codes thrown
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WrenchPincher
User
Jun 1, 2023, 8:16 PM
Post #1 of 16
(2181 views)
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MAPseems bad but no OBD2 codes thrown
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1999DodgeGrand Caravan3.3L200,000 miles
Hi folks,
Can anyone give me an opinion on why my OBD2 MAP sensor reading at idle (or any speed actually) is stuck at exactly 18 kPa when no codes are being thrown and what might be going on?Previously around 38 kPs at idle was normal.It won't idle. I have to keep my foot on the gas slightly.
I can't find any air leaks. No codes thrown at all.My GUESS would be a faulty MAP sensor....but again...no codes thrown.
Thank in advance.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 1:53 AM
Post #2 of 16
(2168 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Enough miles but check for the serious vacuum leak, meaning unmetered air. You should have all kinds of codes it's not reading them. Bulb for CEL burned out? It would barely run.
Again at miles check as best you can for valve timing also will lose vacuum.
Places? If equipped the brake vacuum booster, line(s) to it.
Addition: I don't do Kilopascals for Hg measurements didn't find it on the web just now. How did you get that #?
MAP = Manifold, Actual, Pressure from zero is a total vacuum. Most intake manifold vacuum readings would be around 18Hg or close. Steady with sudden drop with throttle and sudden rise when released.
MAP is trying to do that to deliver correct air/fuel ratio. If all wrong engines won't run well or at all - end of dissertation it's enough miles for this thing for lots of problems,
Tom
(This post was edited by Tom Greenleaf on Jun 2, 2023, 2:04 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 4:02 AM
Post #3 of 16
(2156 views)
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Re: MAPseems bad but no OBD2 codes thrown
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I don't know what you are looking at but MAP sensors don't report in KPA. They convert vacuum to voltage and report a varying reading between 1v and 5v, except on an older Ford which reports in hertz.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Jun 2, 2023, 4:04 AM)
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WrenchPincher
User
Jun 2, 2023, 5:39 AM
Post #4 of 16
(2141 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Thanks Tom.
What's odd is that up until the moment it stuttered and ran really bad...it ran really great.The KPa is from the CarScanner OBD2 android app that interfaces with the Dongle.
It only gives the MAP reading in KPA (or I haven't found the setting to change it)
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WrenchPincher
User
Jun 2, 2023, 5:46 AM
Post #5 of 16
(2140 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Hello,
I use CarScannerPro android app and it gives the MAP readings in KPA.It's no problem for me because the conversion to psi and InHg is easy.
Question, if it is reading pressure, why would it give the test results in volts?I understand that the PCM receives a voltage signal from the MAP sensor but my app and the ELM327 give me MAP in Pressure...not volts?
(This post was edited by WrenchPincher on Jun 2, 2023, 5:50 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 6:24 AM
Post #6 of 16
(2135 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Because that is exactly what a MAP sensor does. It takes a vacuum source and puts it through a potentiometer to give a voltage return to the PCM.
There is no way to see the amount of vacuum the MAP is seeing other than just reading it from another source so the only way to test the output of the MAP is with a voltmeter. There are no KPa readings coming out of the MAP sensor.
NOW some MAP sensors also serve as a barometric sensor reading outside barometric pressure so the computer can adjust for altitude.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 6:49 AM
Post #7 of 16
(2131 views)
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Re: MAPseems bad but no OBD2 codes thrown
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OK, I'll try to be quick. Test for compression my hunch is it jumped valve timing.
Long time issue with shape of these was so much heat on one side of a "V" engine externally didn't seem to exit down and out well so didn't last. There were 4 cyl ones that did OK longer?
Timing chain or gears dictate the camshaft for valve timing somehow off might jump into place then out of place.
Compression would show it. Vacuum starts at zero (outer space) more is "pressure" we (planet Earth) live in pressure of air. That's also about 14.7psi altitude changes it. It ran before my wild guess is valve timing lost adequate vacuum measured and converted to voltage for a computer to do the dirty work. Bad info in, lousy results out so if correct compression would show low, Tom
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 7:02 AM
Post #9 of 16
(2120 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Time to check. Chains jump too and back as said or just quit enough to run. IDK some with a plastic cam gear didn't like the heat some came thru all metal?
Rule it out, it's easy, Tom
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 7:25 AM
Post #10 of 16
(2109 views)
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Re: MAPseems bad but no OBD2 codes thrown
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He can probably get away with just checking the front three to rule out a chain. It's a pain to get the back three.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 9:20 AM
Post #11 of 16
(2094 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Right - just rule that in or out. IDK why a companion shop was forever doing this era WHOLE engines OR the redo lasted better?
Timing chains. Stinks but don't know if metal or plastic teeth only till you are there. I've done other all metal ones twice cared for and all just poor lube no sludge either?
Another tick off was air pick up thru intake snorkel was so low (find cooler air?) one sucked up water just hitting a puddle - bang - game over 1 year old thing! Tom
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WrenchPincher
User
Jun 2, 2023, 9:57 AM
Post #12 of 16
(2090 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Thanks for the help and suggestions.
I believe I found the problem and it was neither a sensor, a module or any engine problem.
On this vehicle, near the throttle body is a large connector with 14 pins I believe.I was looking around for any loose hoses etc and when I moved this connector (which carries the MAP sensor ground and power among others) I could hear a clickingover near the PCM that coincided perfectly each time I moved the harness so I did some quick power and continuity tests and they all passed.
Turns out it was a poor Male to female pin to socket connection. I doubt that connector has been separated in 20+ years.Having disconnected it and re-connected it, it no longer has any issues. Seems the problem is solved and the vehicle runs great again. NO CODES at all.
I'll add some anti corrosion conductive paste to the pins for good measure. I use DeoxIT Copper Conductive Grease
I REALLY love my older vehicles. FAR more than new ones.
Thanks again. Hey, my XTools D7 arrives today! Woot!
(This post was edited by WrenchPincher on Jun 2, 2023, 11:15 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 10:15 AM
Post #13 of 16
(2082 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Thanks for that. Good old "Wiggle Test" connections for wiring!
Now AYOR for it to come back look again if spades to pinch type and also for corrosion. Like dental picks you can make most tighter or some I use tiny needle nose a slight twist on spade is tighter. There's grease "dielectric" is highly water/moisture proof + tolerates heat well use on any and bulbs it's sold as also. Silicone grease is what it is.
Said AYOR but if it's not dependable time to know it unsure if pigtails are out there if bad. You are looking at it so your call,
Tom
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 10:20 AM
Post #14 of 16
(2080 views)
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Re: MAPseems bad but no OBD2 codes thrown
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That tool looks like it does a lot for the price. I've never heard of the manufacturer though.
Nice that it comes with 3 years of updates.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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WrenchPincher
User
Jun 2, 2023, 10:46 AM
Post #15 of 16
(2073 views)
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Re: MAPseems bad but no OBD2 codes thrown
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I'm an old engine builder DIYer for over 55 years. Started tinkering and fixing mowers etc around 8 haha.No formal training like you guys have tho.
I've had OBD scanners since 1996 but this D7 is the most advanced diagnostic tool I've ever had.And probably more than I need but I'd rather have it and not need it...you know the saying.There's lots more advanced stuff....but I didn't wanna spend more than $600This D7 should do me good. I did also order a D8 and will decide which one I keep after I've used them both.
I pulled and rebuilt the motor in my later model Dodge about 3 years ago. When I got it dirt cheap it had never had an oil change and the bearings were trashed. They were STILL driving it !!!
The one I mentioned in the OP is on the schedule for a full rebuild soon.
I said 200,000 miles to be brief, but it's actually closer to 300,000 miles....and still going strong. A bit down on power and fuel economy tho.
I plan to keep these vehicles going for my lifetime.Big concern I have is failure of electronics inside the resin encapsulated PCM, TCM and ECM etc. Capacitors and stuff only last so long.Getting all that gook off the PCB is a nightmare. Finding a suitable replacement will get next to impossible.My hobby is electronics repair so fixing those circuits would be right up my alley ;-)
I hope you both have an excellent weekend and I'm sure I'll be back with more dumb questions soon.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2023, 10:50 AM
Post #16 of 16
(2068 views)
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Re: MAPseems bad but no OBD2 codes thrown
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Good luck, I'll close this now as solved.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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