home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > maintenance & nonperformance

Reply
 
Thread Tools Display Modes
Old 02-25-2021, 06:05 PM   #1
Timisawesomeish
Newbie
 
Join Date: Feb 2021
Default failing smog, very rich when engine hot

I apologize if there is already a post about this but I am new and I couldn't find one. I have a 1986 740t wagon that I am trying to get passing smog. has a brand new cat, o2, and coolant temp sensor. Symptoms are passes when engine is cold at 15mph but fails 25mph. With engine warmed up fails both as gross polluter. I also tried replacing the AMM with another 007 from a junk 240 which did nothing as well as a reman from Delphi (a10335). The reman made the car idle terribly and run super rich. Any ideas that could help me out here?

edit: forgot to include it is failing for CO and HC
Timisawesomeish is offline   Reply With Quote
Old 02-25-2021, 07:59 PM   #2
dl242gt
Happy playing the blues
 
dl242gt's Avatar
 
Join Date: Jun 2002
Location: S NJ, a suburb of Phila.
Default

Have you tuned the engine up? New plugs, cap, rotor, and wires go a long way to helping a rich mixture. How was the wiring on the coolant temp sensor that was replaced? You want to measure that circuit by testing at the ecu connector for the proper impedance at temperature. Alternatively you can measure the voltage on the sensor and see that it progresses properly according the information on cleanflametrap.com.

Don't forget the air filter. A clogged air filter can make the engine mixture rich.
__________________
Dave,
1982 242 turbo. 338k miles. MVP coilovers and 3" exhaust. Flowed 405 with a V15. Cossie turbine housing with upgraded compressor housing. 90+, IPD remote oil filter. Some other goodness, too. Been lots of fun over 25 years. Restored in 2k. Now ready for a 2nd restoration.

1993 245 Classic, 430k miles, enem V15. IPD bars and chassis braces. Simons sport exhaust from Scandix. sbabbs ezk chip. Been a good road warrior. Genuine Volvo rebuilt leaky M47.

Last edited by dl242gt; 02-25-2021 at 08:00 PM.. Reason: add comment
dl242gt is offline   Reply With Quote
Old 02-25-2021, 08:37 PM   #3
PCH
Board Member
 
Join Date: Oct 2008
Location: Oxnard, SoCal
Default

Seeing the actual numbers from the report (CO2, CO, HC, O2, NOx) and limits would help.
How "cold" is the engine when it passes @15MPH? They are not even supposed to test unless its at normal operating temp.
PCH is offline   Reply With Quote
Old 02-25-2021, 08:41 PM   #4
Timisawesomeish
Newbie
 
Join Date: Feb 2021
Default

Oh yes I forgot those were the first things I went after. Changed the plugs and wires (had a miss from one wire arcing). Checked cap, rotor and air filter, they seemed fine. I did some testing after posting and I don't believe it is going into closed loop.
Timisawesomeish is offline   Reply With Quote
Old 02-25-2021, 08:47 PM   #5
dl242gt
Happy playing the blues
 
dl242gt's Avatar
 
Join Date: Jun 2002
Location: S NJ, a suburb of Phila.
Default

If it never goes into closed loop operation. That is a sure sign that the coolant temp sensor circuit is having issues. It's the most important circuit as it overrides the ecu wanting to go into closed loop. If the sensor has too high a resistance like an open or high impedance. Then you get a rich mixture all the time.
dl242gt is offline   Reply With Quote
Old 02-26-2021, 02:51 AM   #6
MasterBlaster
Board Member
 
MasterBlaster's Avatar
 
Join Date: Feb 2009
Location: Port Coquitlam
Default

Check the fuel pressure regulator too, on the front end or the fuel rail. Pull off the vacuum hose and see/smell if there's any gas wetness in the hose or coming out of the fitting.

If the regulator's diaphragm ruptures, the regulator (a) won't close and lower the fuel pressure to where it should be under vacuum, and (b) will let raw unmetered gas get sucked through the hose into the engine. Both will make it run way too rich.

Also, if the hose itself is split or leaking, no vacuum is applied the the regulator, and it runs rich.


__________________



1990 740GL, now in extra-small economy size.
513,000 km so far...
MasterBlaster is offline   Reply With Quote
Old 02-26-2021, 04:55 PM   #7
Timisawesomeish
Newbie
 
Join Date: Feb 2021
Default

Ok so checked fuel pressure and it sits at 3 bar steady. I'm a service writer at a volvo shop and my 2 techs keeps saying it's the AMM. I've tried several used ones with no luck. My last chance before forking over big money for a bosch reman would be trying the one from my 88 240dl that is my daily. My boss is convinced that it's is a fault in the cts circuit and I noticed there is oil and gunk all over the wires under the intake manifold so I'm going to take the manifold off and clean up all of that today. I'm out of the shop for the weekend now though, so access to diagnostic tools is limited.
Timisawesomeish is offline   Reply With Quote
Old 02-28-2021, 02:38 AM   #8
Khrrck
Professional Amateur
 
Join Date: Mar 2015
Location: Beaverton, OR
Default

Do you know if it has the original harness or not? possible the insulation on the sensor wiring has rotted.
__________________
'87 240 budget wagon.
Quote:
Originally Posted by Dirty Rick View Post
Navigating the Siskiyous in a 3 wheeled Volvo will not end well.
Khrrck is offline   Reply With Quote
Old 02-28-2021, 01:11 PM   #9
ZVOLV
<Master Tech>
 
ZVOLV's Avatar
 
Join Date: Nov 2002
Location: California
Default

On my LH2.2 740 Turbo, it ended up being leaking injectors causing the rich condition.
__________________
No Start Thread
ZVOLV is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 08:48 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.