951 Failed Emmisions with High HC

[kiwior]

Recently a friend of mine took his '89 951 for the emissions test and failed with a high hydrocarbon reading. The car is stock with 29,000 miles and was tested in Illinois on the dyno machine. Any suggestions??

He checked the fuel pressure, gauge is showing low pressure, would this cause high hydrocarbons???

[Blackfoot]

check the o2 sensor first.

[Scott R]

Hydrocarbons are unburnt fuel particles exiting the exhaust system. Primary cause is usually vacum leaks in and around the intake manifold. You may also have a rich burn condition due to a clogged up throttle valve. And also check and clean the AFM. But first and foremost check for leaking vacum. How far over did he go? what % of normal.

[kiwior]

Hi Scott,
Thanks for the info. He took the test twice and failed both times. After the first test he replaced the air cutoff valve (not waste gate). It had a torn diaphram. His results were as follows:
1st test: 1.79 gpm
2nd test: 2.32 gpm
Required HC value < 0.8 gpm

Mark

[DennisR_944]

Somewhere at the 944 Garage there is a chart that shows how to reset the DME by setting at different notches to reduce or increase the timing and fuel mixture. Check there and maybe change the mixture and test again? Just a thought.

Dennis Russell

------------------
Dennis Russell
Indianapolis, IN USA
1987 944 n/a

[mlue]

Coincidence or what I just passed emmissions test last nite after months of trying to get my car to pass. In the process I have found that the too most important things required to pass the test if everything else (plugs, wires, cap and roter) are OK (1) Oxygen sensor (2) Catalytic Converter. These 2 work togeather. When I bought my car the cat was burnt out, it failed the test with high HC. I replaced the cat and the car failed again but the HC level was only slightly above the limit compared to the first test where the levels were through the roof. The car failed the second time due to a high CO level. I replaced the O2 sensor with a universal and made sure the allen screw on the AFM was adjusted to the same amount of turns as the one on my friends car (previous owner had played with it, the cap for the adjustment hole was missing). The car passed with flying colors last nite.

The technician says that if you have a bad O2 sensor or the car is running rich it will burn out the cat after a while. It the cat is burntout, after a hard drive you will not smell the sulfur smell just raw exhaust.

I hope this helps.

Mark
'86 944NA

[This message has been edited by mlue (edited 09-06-2001).]

[Ehab]

Hey Mark, could you help me out by telling me how many turns to turn that thing, I tried adjusting it for many many months, after I originally found it unscrewed almost all the way up. I had to increase the tension on my AFM spring because the car was running too rich, and 'hunting' rpm during idle. Now I have it all the way down, and that seems to keep the idle stable at 950 ...

I would really really appreciate it if you tell me the details of what you did, since i have to get the inspection sticker soon (2 months overdue!!)

thanks.
E

[mlue]

Ehab, I am happy to help in anyway I can as you and Ahmet helped put me on track. I was originally going to reindex the AFM as you and Ahmet described but a friend of mine talked me out of it as I would have been adjusting too many varables with out any benchmark. We only did one change at a time using his car for comparison. My car does not exhibit any hunting at idle at all even when I have adjusted the allen screw but the pitch of the engine and the response were different. The previous owner had adjusted the screw to only 4 turns (rich) from the bottom. My friends allen screw was covered by the plug was stock until we turned it all the way in, about 9 turns to get the benchmark. The hole around my allen screw has a slight shaddow from the position that the screw was at from the factory, when we adjusted the screw 9 turns from bottom we actually went about a turn or so past the shaddow but because his car past the emmissions test who am I to argue, so 9 turns was used. Looking back at the results for the test which showed a slightly high but acceptable NO (Nitrous Oxide) level, I could probly turn the allen screw in about a turn because a slightly High level of NO indicate a slightly lean condition.

This adjustment to the idle mixture and the O2 sensor and the cat made the biggest difference with the emmission test. If you think your cat is still good replacing the O2 sensor is resonable if you get a universal one I beleive $30 for the single wire and $45US for the 3 wire (Bosch 13913) at Pepboys. I replaced the original burntout cat with a CATCO ($79) one that they use on V8 engines. I donn't see any performance problems as my '86 runs just as well as my friends '87 with original cat and O2 sensor.

The original rich condition could be just a bad O2 sensor that you have compensated for by reindexing the AFM. By changing the O2 sensor you may establish new base lines from which you can get back on track.

I know you have an Idle speed problem maybe this page will help you find the source of your problem:

http://porsche-944-garage.tripod.com/shop-manual/fuel-08.htm

Mark
'86 944NA

PS. This may not make a difference but I also replaced my alternator Voltage Regulator/Brush Holder assembly ($23) to ensure that the voltage supply to the DME and all electrical devices were steady.




[This message has been edited by mlue (edited 09-06-2001).]

[mlue]

kiwior, I think the cat on a 951 is setup a little different and is not as straight forward as a 944NA, hence the more complicated exhaust plumbing. I may be mistaken but isn't there some sort of air pump that supplys air to the cat to aid in the catalyst action. If this pump failed ???

Has any of the exhause pipes between the engine and the O2 sensor being remove and reinstalled ? If there are any air leaks in the system prior to the O2 sensor this could cause the sensor to read a lean condition and conpensate by richening the mixture.

I would still check the O2 sensor though, cann't hurt!


Mark
'86 944NA

PS. I know I have written alot, so I will be quiet now !!! ;~)

[kiwior]

Thanks for all of the input everyone. Mark, we are going to check the exhaust this weekend.
Once again thanks to everyone for the great information and help!!
Mark

[Ehab]

Thanks Mark,

I actually replaced the O2 sensor before re-indexing the AFM spring, so no worries there, and I also replaced the voltage regulator/brush holder for the alternator just recently ($15, thanks to Dave951). My car is running fine now, and the idle is not hunting anymore, but I guess I should wait to do the emissions test to find out if I'm too lean or not. But judging from my gas milage, I think I'm close to stoichiometric ...

How did you know your Cat is burnt out?
Did you have to do any welding to replace it?
I'll keep you updated ...
E

[mlue]

I was lucky depending how you look at it, my cat was bearly working so it was easy to troubleshoot. When I came into the pits after a hard run with lots of WOT around the track at Mosport there was no hint of the sulfer smell just raw exhaust like a "60 musle car. When I took it to the muffler shop they confirmed that the cat was not working. They said that when the cat is working the temprature of the exhaust coming out of the cat is alot cooler when compared to the temprature of the exhaust going into it. The Porsche cat is long, the front part houses the catalytic material and gets really hot and the back part does something but mostly acts as a resonator. It wasn't long after I arrived at the shop when they removed it, the guy was able to hold the cat in his hands. After replacing the cat there was lots of sulfer smell while driving, more than most cars so I knew it was running rich. I did an emmissions test after the cat replacement which it failed but there was improvement. I think I covered the rest in my previous posts.

Mark
"86 944NA

[rob'smobile]

Unplug one injector it will pass my hc at idle was 276 before and 165 after, John W. gave me the tip. It works!!!!

[nynor]

whoah resurrection of a 6 year old thread!