Emissions issue on 1987. 350 w 700R

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Sure thing. My email is snipped-for-privacy@oplink.net
snipped-for-privacy@webtv.net (Bill S) wrote in message


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A couple of things I should have mentioned previously. It is a typical 350-TBI set up, I think this was the first year for it. It doesn't seem to have any miss or stumble which I attribute to the Jacobs ignition system which has been on for some years (it used to miss a lot at idle and stumble rolling off idle). It does seem to idle a little high but it always has. It has 170K miles and the original CAT, original injectors, and the original heads and engine internals. Don't start throwing stones all at once. :-{
I mentioned that I changed the EGR valve recently when troubleshooting a rough idle which turned out to be a vacumn leak. How would I check for an "over active EGR valve"?
How did you make the calculation of the air/fuel ratio? Could you please expain for us mortals?
Ken K
snipped-for-privacy@oplink.net (Ken K) wrote in message

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snipped-for-privacy@oplink.net (Ken K) wrote:

At 170K miles, it might just need a new cat. Question; does your ignition system retain the original distributor housing? If so, take off the distributor cap and closely examine the magnet in the center of the pole piece for cracks, the cracks usually radiate from the rivets which hold the laminations of the pole piece together. Cracks = bad running.

Rear tires off the ground on stands, engine running in gear, accelerate (open the throttle) and observe the EGR action which you'd probably need to do by feeling the diaphragm with your hand. It's one of those things that comes to be recognized by experience and practice comparing good against bad. Most bad ones (over active) tend to open close to full stroke... Naturally, any changes in the exhaust system that effect back pressure can also be a cause of an over active EGR valve since the one used on your truck is back-pressure modulated.

The one I use is an online Lambda calculator which is only available to professional mechanics.
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Yes, I'm still using the original distributor. The additional system uses a huge high power coil and it's own external computer in place of the coil and ignition module. A side benefit is that I leave the old parts in place and can plug them in if the high powered stuff were to fail. The downside is that it requires pricey plug/coil wires and a 0.65 spark plug gap. The wires and plugs do last a long time though, several years at least. I also index the plugs which seems to help. It also needs a high quality cap and rotor which always was the case with this truck even with the regualar set up. It really fires hard with this system and no more skiping and missing at idle and stumbling when accelerating of idle. Believe it or not the gas milage went about 12 to about 14mpg too. I think on this vehicle is was worth the money, it's been on there about five years.
Thanks for the tip on the magnetic pick-up coil and EGR valve. I will definately check that out. It there a check for Ohms or something on that coil? And is there an easy way to know if the CAT is bad?
Ken K
(Ken K) wrote:

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snipped-for-privacy@oplink.net (Ken K) wrote:

Well, the thing is, one shouldn't have to resort to a Jacobs or MSD ignition system in order to get the engine running correctly. The stock GM HEI although it has its faults, should be more than up to the task unless the engine has significant modifications.

Yes their is, but the chronic failure seen in that particular pole piece can be identified visually. Look for the cracks in the magnet. The cracks play havoc with the ignition timing and dwell schedule in the module.

Not really. If one has a gas analyzer, he can perform pre-cat and post cat gas reading to see how well the gasses are being converted, GM has a slick test where a pre-warmed cat is flooded with a calibrated amount of propane, a CO2 reading taken and compared to an efficiency chart.
I think the reason for the emissions failure lies in whatever is the root cause behind -why- you need an aftermarket ignition system to make that truck run halfway decent.
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this is way to technical for me but here is my suggestion. take it to "the other side of the tracks mechanic" or stop in some back-woods town and have it done there. my bet they will either take a 20 spot to look the other way or if Buddy in Dimebox, TX looks at it they won't have sniffers.

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have you changed the oil & filter recently? the unburned gasses from the miss can build up in the crankcase and will cause the hc to be high.
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