Of that I have no doubt. Many conditions cause failed emissions tests for many reasons. Some cause high this, and some cause high that. I allow that a stretched timing chain may be among them. But in this particular situation, overwhelming evidence of high combustion chamber temps, I would need to see exactly how a stretched timing chain leads to high combustion temps before going through the trouble of replacing it. If I was convinced that it is the cause, then game on. Break out the wrenches and go to work.
But in this situation, first eliminating all the MORE LIKELY conditions that cause high combustion temps, conditions that are KNOWN to cause high combustion temps, makes sense, and to me, making sure that the cooling system has every chance to do its job is paramount. A water jacket that has an insulating coating of rust is much more suspect in causing high combustion chamber temps than a stretched timing chain, which by the way, is stretched only to the point of having 7 degrees of slack. Given that the engine runs very well at all speeds, starts with one or two seconds of cranking, is another argument not to agonize over 7 degrees of slack in trying to bring down the combustion chamber temps.
I challenged tester to explain exactly how a stretched timing chain can cause high combustion chamber temps, and he did not do it, nor did he link to anything that did. If you think you can, have at it.
This thread is getting like the lawyer who could not convince us he was correct even after everyone posted to the contrary and then he signed over and out.
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It seems that there is a big assumption here that the combustion temps must be high. Has that even been checked? It was mentioned that the cat in and out temps were checked with an infrared thermometer. How about using that tool at the exhaust manifold ports to get an idea of EGTs?
I have replaced worn timing chains on Dodge trucks, because they were noisy, not for failing an emissions test.
Years ago I bought a 1995 Ram 3.9 L, the chain was so worn it was slapping the timing chain cover. That truck passed the emissions test but we donāt check oxides of nitrogen here.
Do they perform emission testing in his county? In Minnesota?
Against my will, Iām gonna butt in as this thread is getting too stupid.
OP
Youāve got a helluva lot of good advice, but You seem to be quite ignorant of it.
You obviously donāt know how the intestines of an ICE engine relates to each other. I donāt mean this in an condescending way.
Problem is - if You have a stretched timing chain - not only the valve timing is off, but Your ignition timing is off too. In an expensive way unfortunately.
Late valve timing will cause the combustion temps. to rise slightly, but late ignition timing ( with reference to factory specs) will cause a steep increase in combustion temperatures as the burning will be slow - timewise - and on the downstroke of the piston. The biggest problem is, that You will most likely not notice it on the temp. gauge at all, as most vehicles of Your style and age has a somewhat oversized cooling capacity
I have made an engine swap on a car (we are back to points and condenser) where on the following testdrive, the engine oil started to boil. That did not look pretty in the rear wiew mirror. Back to the stable and the investigation started.
Turned out two of the points on the distributor axle was worn out, cyl. 4 to the point of igniting 17 degrees AFTER tdc and cyl 2 8 degrees AFTER tdc.
Those two cylinders (out of four) was enough to make the oil boil, BUT AT NO TIME - I repeat , no time was it showing on the temp. gauge. Not by one degree. And the temp. gauge and associated parts are still working fine, so no - it was not a defect sensor or the like.
You have 8 cylinders firing at a very late point and that will cause a significant increase in comb.temps. Iād like to know the temp. of Your engine oil after a long run.
Youāve got good help here. If You donāt wanna take it, no problem, but have the decency to say so and bow out in a dignified manner.
Best of luck and stay safe.
And now Iāll bow out for good.
Adios, goodbye, farvel, au revoir.
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pull the distribator cap off turn the crank back and forth if the crank turns and there is no movement on the rotor cap the chain is stretched out
A point is a good thing to be able to figure out. With the camshaft turning the distributor, you get retarded ignition timing as well as valve timing. So I went back and read asterix post and he mentioned that. So I was late. Weāll all live. Iāll bet there is a lot more wrong with the engine by now. The exhaust valves may be loaded with deposits and some might be burned with slots in them. It could be time for an engine or a rebuild.
Omigod, I just checked in after working on my truck and I find this thread at the top of the list. I havenāt read anything new, but here is an update, for those who care. I drained and flushed the coolant, and added a rust dissolving compound, which, for the time being, shall remain unknown, but it dissolves rust, or so I am told. I will leave it in the cooling system until such time as I deem appropriate, then I will drain, flush, perhaps neutralize (it is acidic), and then perhaps I will add more rust dissolving chemicals, either acidic or chelating. Or perhaps I wonāt. It depends on how Iām feeling.
Fate has given me this amazing 1987 Dodge Dakota pickup, with an 8 foot bed, and a ton and quarter payload, and, thanks to Enviro-Safe, the air conditioning still works.
I would like to sincerely thank tester, who gave me a link to possible cause of high NOx, and to the individual, you know who you are, who gave me the link to the vacuum meter tutorial. I really appreciate that. I have been looking for that. It is nice to find it. Thank you so much for that! I remember getting similar information with the very first vacuum meter I bought many years ago.
Well, thatās all for tonight. I will certainly check in again to update anyone who gives a frock on the progress of getting this wonderful 1987 Dodge Dakota to pass itās 15th or so California smog test. Wish me luck!
Wow, thank you so much for your very thoughtful reply. I really do appreciate it. I will certainly absorb it in the days to come. As I have indicated, I want to eliminate the possibility of rust in the water jacket insulating the combustion chamber from the cooling effects of the coolant flowing through the water jacket, as I suspect this rust insulation is contributing to high combustion chamber temps, resulting in the formation of large quantities of nitric oxide, causing failure of the three-gas smog test.
Dang! So THATāS why I have been burning oil like crazy! Whoāda thunk?
A loss in cylinder pressure at low rpm would result in lower combustion chamber temperatures.
Of all these timing chains offered by RockAuto, which is the bestā¦ or is there some other timing chain that is better? If removing rust from the water jacket does not reduce combustion chamber temps, I just may give it a go.
https://www.rockauto.com/en/catalog/dodge,1987,dakota,3.9l+239cid+v6,1087343,engine,timing+chain,5724
Scroll down to āTiming Setā.
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False economy to just change the chain and not the gears, too.
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Have you applied vacuuum to egr w manual pump and that stalls engine at idle?
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Yes, Welcome back @George_San_Jose1
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Thanks, George, Although I have exhaustively determined that the EGR system is operating as it should I will do this today to further ensure its correct operation.
