87 5kcsqt not passing emmisions...HELP!!!

Ameer Antar ameer at snet.net
Thu Feb 1 15:13:45 EST 2001

Usually a bad cat will cause NOx emissions...do you guys not test for this? 
If you don't know about NOx, the cat could be the problem. But first you 
should verify that the mixture is set right. You need a dwell or duty cycle 
meter which should read 45 deg. or 50% at idle off the CIS frequency valve 
test connector. Also replace the o2 sensor if it's older than 30k. Check 
for vac. leaks. Vac. leaks before the turbo [between air-flow meter and 
turbo inlet] will ALWAYS cause lean running. After the turbo [between turbo 
outlet and throttle body will cause lean running under vacuum and rich 
under boost. Leaks are hard to spot and you really must remove the intake 
hoses to see all the hidden cracks...80% chance you have cracked hoses if 
they've not been replaced yet. Check condition of ignition system, as well 
as fuel issues...ie. old injectors. Injectors usually last 80-100k miles. 
good luck.


At 01:23 PM 2/1/2001 , you wrote:
>Hi all
>I have a 87 5000 csqt with a hoppen chip that passed emissions last year 
>with flying colors...this year it failed miserably on both the HC and the 
>CO tests. The max allowed on the HC is 220.00 and my car was 682.00, the 
>max allowed on the CO was 1.2 and the car measured 7.3. I have just 
>completed the input and output tests according to SJM's site and no faults 
>were found. I am a little stumped here. The car runs and drives fine. I 
>have noticed that the max boost has diminished a little... I used to get 
>16-17 psi all the time and now I can only muster 15-15.5psi...the boost 
>used to spool extremely fast from 10-17psi, as soon as I would pin it ... 
>the gauge would shoot to 16-17psi... now it slowly builds to 15. Could 
>there be a vacuum leak somewhere that is causing the rich mixture and the 
>boost problem???Or is it my imagination???Thanks in advance
>87 5kcsqt
>91 200 20v

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