Source: Ian James - LT5 Engineer
There are lots of elements to producing a passing emission test result. Once you've found that happy place, staying in it can be difficult. One of the official tests checks the time taken for the car to decelerate in neutral on the chassis dyno between two speeds. The elapsed time needs to fall in a 'window' which confirms the correct dyno load (resistance) is being used. As we got closer to certification, this test became more important to us. We began to find in late Sept '88 a tendency for the car to run longer and longer coastdown times. This was a feature of the 315 rear tires which polished up on the dyno rollers and so contributed less than their expected share of rolling resistance to the whole vehicle. The more tests that ran the greater the polishing effect and the greater the danger of failing the coastdown 'quick check'. For us, this was one of the reasons why there are only so many good runs in a Cert Car. The easy answer is to take your treasured Cert Car out onto the proving ground out of sight and give the rear tires a damn good seeing to! This in a car that's only ever done a controlled cycle of mileage accumulation to 4000 miles. There are huge risks in even just taking it outside the emission lab. Such cars are beyond priceless in $ terms.
The way the process worked was that the car got tested in the GM VEL – the corporate Vehicle Emission Lab rather than the CPC Group development facility. There was a known correlation with the EPA at Ann Arbor and so when we had good test results that worked at the VEL, the official channels submitted the data and the car was called to EPA for a 'confirmatory test'. It then just had to do what it did before.
Towards the end of Feb '89, P8Y095 had reached 4k miles. Through early March we fought with a car that didn't work in the lab - fuel rails/injectors, air pump wiring and the air divert valve vacuum system. Finally, by 9th March, we had produced acceptable passing results at the VEL.
A test at EPA was scheduled on 17th March and off we went. I think I remember John Bloomfield (Lotus Engine Management Group Leader and Certification guru) being there at ACR's request, just in case.
As manufacturer's representatives, we weren't allowed anywhere near the car on test but somehow, I know that the young lady who came out to drive the car was a Corvette nut. She had kicked off her sneakers to drive the test in bare feet and I offered up a silent prayer of thanks! We got the result – the car had passed emissions but the fuel economy was off. Depending on how the numbers were rounded and processed we had avoided gas guzzler or not. Of course, EPA said not! Aw s**t!! The wheels were coming off! This kind of experience is 'character building!'
Looking at the numbers, the progression of fuel economy through the three parts of the cold FTP was wrong. The middle phase was never lower than the first. Our middle phase was less than the first. That suggested a major screw up, but the emissions were sound and the car had driven perfectly the driver's report said. It seemed to me that the only thing that could explain this was that my favorite driver in the whole world had shifted out of 4th in the long low speed cruise (cycle 11 for the sad amongst us) and gone straight forward into 3rd not 5th. The next hurdle was that I was 99% sure that I knew what had gone wrong but we could do nothing until we heard the result through the proper channels and thus make a request that EPA consider our argument.
Well EPA listened, and declared that their staff didn't make that kind of mistake, but on this occasion they would grant us a retest - but we had to average the economy result with the first test! Now don't forget the slick running rear tires! Strangely, we couldn't just take the car away and scuff the tires.(More character building!)
A new test date was scheduled for the 21st and I drove the Ann Arbor alone this time in P8Y094. (I wonder why that was?) 'Big Jim' came out to drive the car, he really was substantial guy and my heart sank! But - he drove the most perfect test that I'd ever seen. The numbers were crunched and we'd avoided gas guzzler by 0.03 mpg (US).
Here are the two EPA FTP75 emission test results from P8Y095 in March '89 and a copy of the 'Certificate' - The piece of paper that it was all about.
From Tyler Townsley regarding the last image: "The car may have been an 88 but the engine was a Phase III. All P8Y cars came with Phase II motors which did not pass the 400 hr test. It was a Phase II motor modified with the duplex chains that passed the test in late 1987. In Dec 1987 there was a meeting where it was decided to go ahead with the production. Virtually all Phase II engines self destructed under testing."