Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 914 & 914-6 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Jan 2002
Location: Calgary,Canada
Posts: 263
Garage
CHT resistance question...

Hi all...I just checked my CHT sensor resistance with a meter and it's around 1600 ohms.
I understand it should be between 2000 and 3000 ohms cold.
Should the sensor be replaced? Or is it close enough?
Cheers
Mike
Old 06-12-2010, 09:01 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: Jan 2002
Location: Calgary,Canada
Posts: 263
Garage
Sorry....the car is a 74 2.0 litre.
Old 06-12-2010, 09:06 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Jun 2010
Location: Central Massachusetts
Posts: 17
Mike,

I have been having the opposite problem with my '73 2.0, which uses a different sensor. First of all, the resistance you measure is VERY much dependent upon temperature, so even holding it in your hand can have a measurable effect upon your reading. Second the '74-and-later 2.0 uses a different CHT from the '73. Yours should be the 0 280 130 012, which has the higher resistance. Mine should be the 0 280 130 017, which is in the 1600 ohm range, at about room temp. You can get the full story, as well as more Resistance/temperature info at (or some such) website, where he discusses just about everything you'd want to know about the D-jet F.I. system.

You MIGHT have the correct sensor. It depends on your ECU and MPS. If yours are both stock '74, you should have the 012. BUT, look at that website first, look at your sensor to read the (Bosch) part number and measure it at one of the temperatures in Brad's article before you change anything. If you DO decide you have the wrong one, I have an 012 that I would be happy to trade for an 017, if that is what you have. Just check all of the above first.
Good luck,
Jim
Old 06-13-2010, 05:08 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Jun 2010
Location: Central Massachusetts
Posts: 17
Mike,

Sorry.... That website didn't come out in my first reply to you. it is Brad's '70 914 2.0L

Jim
Old 06-13-2010, 05:12 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Jan 2002
Location: Calgary,Canada
Posts: 263
Garage
Thanks Jim...I have read and printed most of the info on that site.
Probably more than I wanted to know about D jet!!!
I am measuring the resistance of the sensor that is in the engine right now so I am only assuming it's the correct part. I have also read the stories of people that can't get the old sensor out and end up dropping the engine et. etc.

It measures 1500-1600 ohms cold. Should it be replaced?
Cheers
Mike
Old 06-13-2010, 05:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Administrator
 
Dave at Pelican Parts's Avatar
 
Join Date: Dec 1969
Location: Silly-Con Valley
Posts: 14,062
Garage
Send a message via AIM to Dave at Pelican Parts Send a message via Yahoo to Dave at Pelican Parts
It's a pain to replace, so I vote for leaving it in there. Do you think you're running lean when the engine is cold?

--DD
__________________
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling
Old 06-13-2010, 08:28 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Jun 2010
Location: Central Massachusetts
Posts: 17
Mike,

Ahh, Dave has asked the important question! If you are not running lean, then use the one that is in there. How does it run?

It is a little tough to get out. Brad's website describes how to take it out, if you need to. I have done it Brad's way, and it came out OK for me. Whether is is "correct" for your engine depends upon the ECU you have. See Brad's list of parts.

Jim
Old 06-13-2010, 04:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
Join Date: Jan 2002
Location: Calgary,Canada
Posts: 263
Garage
Thanks for the replies guys....the car starts great,fast idles for a while,slowly comes down to 1000 rpm. It just feels really sluggish and hesitates, especially when warming up. I know the CHT sensor is doing something because I left it disconnected and the car wouldn't start. I have cleaned the contacts and circuit board in the TPS but that didn't make a difference. I'm having a hard time adjusting the TPS because I can't get the probes from my meter to stay put. I'm not sure which pins I'm touching because of the orientation of the TPS...any help there?
Cheers
Mike
Old 06-13-2010, 06:45 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
Join Date: Jun 2010
Location: Central Massachusetts
Posts: 17
Mike,

I have no experience with the TPS. From what I read, it MAY be causing your problem.
It also sounds as though the symptoms you experience may be caused by a too-low resistance at the CHT. You COULD test this by adding a ballast resistor (from Radio Shack?) of ~270 ohms (the value of the one that goes with the 017 CHT---but maybe not with your ECU) to see if that corrects the problem. I am not sure how you can tell if this would simply mask a bad TPS, though.

Can you see a part number on your ECU? Brad's website lists which ones go with the '74s. The part number on mine was right on top of it.

Another thought: If you decide to take out the CHT, my suggestion would be to warm the engine thoroughly first, as the head is aluminum, which expands faster than the steel sensor. This may make breaking something less likely.

Jim
Old 06-14-2010, 03:00 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
Join Date: Sep 2005
Posts: 140
Mike re your TPS there is a Pelican article about TPS adjustment which you should have.
I use alligator clips on my multimeter to get onto the #12 and #17 lugs, using a mirror to check that I have the right ones.The lower plastic cover clips off to give more access.
If your CHT is reading 1600 ohms at cold then it is probably an 017 when you need a 012/03(these 2 read over 2300 cold)
If you decide to remove the CHT then you should be generous with the WD40!
Geoff
Old 06-25-2010, 02:52 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: Feb 2008
Posts: 5
The question is not what the cht reads cold, but rather what it reads HOT, since the problem occurs after warm up. They can fail open (0 ohms) which causes a rich condition and bad driveabiity. Check it after the cars been run up to operating temperature.
Old 06-26-2010, 03:10 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
Join Date: Jun 2010
Location: Central Massachusetts
Posts: 17
Trade? Just a reminder.

Mike,
How are you doing with that drivability problem? As I said earlier in the tread, I have the opposite problem---a '73 with an 012 CHT. I also have a spare 012, which I am willing to trade for an 017, which you may have. If you DO have an 017 and want to try an 012, I could send you my spare and you could try it. If it solves your problem and you want to keep it, just send me your 017. If it doesn't, just send me back my 012.

If you warm the engine first and use Brad's method of taking out the CHT, it should work. Just be sure to grind a nice deep groove in the wrench extension for the wire to pass through the socket undamaged. There is also a special socket available with a slot in it for the wire. You need a 13 mm.

Would this help?
Jim
Old 06-27-2010, 08:15 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 05:30 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.