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Discussion Starter · #1 ·
Have any of you guys noticed that your engine seems to knock with 87 octane? I thought my engine might have been knocking on 87 and it seems smoother on 89. Is there any truth to this or is it in my head? This is in my 99 Vulcan
 

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I haven't heard any knock on my '03 flex-fuel Vulcan, but it does seem to idle more smoothly on BP and Shell gasoline than it does on Marathon. But then, that might be my imagination, too.

Its performance on E85 is a topic for a whole another thread!

My wife's (Toyota) van definitely pings on 87 octane, on all brands. It's not quite as bad on BP, though.

Have you tried different brands of fuel, comparing one brand's 87 to another?
 

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How many miles? If there's a ton of carbon buildup in the combustion chamber, your compression will go up and cause it to ping on lower grades of fuel. If it's high on miles, seafoam will clear it up.
 

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I had a '99 vulcan and it is true, they knock on 87 all the time. I dont think there is a knock sensor in the '99's BTW. I changed over to 89 and the knock went away and I noticed an increase in milage as well on the highway with the cruise set @70. (my standard highway driving). This is a fairly common problem, though some dont think its worth the couple $$ on a fill up, after checking milage, it was worth it in the long run. You wont have any damage if you run 87, but the knocking will drive you crazy in time..LOL :eek:
 

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You are correct dlc360. 97-01 werent blessed with knock sensors. 96, 02-07 had them. I like the decarbonization and higher octane ideas.
 

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Discussion Starter · #7 ·
I have almost 126,000 miles on it and its been kept up well with no major engine problems all stock internals. I seafoamed it within the last 10k miles and i got almost no smoke out the exhaust, so i am thinking its pretty clean.

I am going to seafoam it again when i get more money as well as a few other things on my to do list.

I knew it didn't have a knock sensor which is why i was asking. I think i will keep trying the 89 octane and see how it goes.
 

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10k shouldn't build up too much carbon. Check your CPS. The sensor can break without the shaft making the tell-tale squeaking noises, and then your PCM will constantly advance & retard timing similar to a hunting idle. It could be that it's advanced timing enough to ping with 87 fuel. When my car did this, I was running 91, so I'm not sure if it actually advances that much, but it's something to look at.
 

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You got my attention. I know where cps (crankshaft position sensor?) is. Where is knock sensor?

How do I know cps or knock sensor is bad?

Thanks.
 

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Discussion Starter · #10 ·
Where is the CPS located and is it a simple bolt on part or do i need to remove or adjust anything?

I have been having this hunting idle problem as well so now i am concerned.
 

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The cps is located under the tb where the distributer used to be. It makes it a lot easier if you have the tool. I hear the best way is to get the cheap dorman cps that comes with tool and chuck it and get the motorcraft one to put in. I'm not sure how easy it is as I haven't had to do it yet.
 

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Theres a bajillion threads on the cps and crank synchronizer. Do a search. Might be a how-to in the topic finder, wiki or solutions to common problems section. I think proford posted the first?
 

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Unbolt the throttle body and see if your EGR passages are carboned. Seafoam is great, but it can't fix everything.

BTW cam sensor should be referred to as "CMP" and crank as "CKP", otherwise people get confused and start buying the wrong parts.
 

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Its performance on E85 is a topic for a whole another thread!
You should NEVER run E85 on your vehicle unless it's a FFV vehicle or designed to run E85. :eek:
 

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Mine will always get some ping in it whenever the air becomes very dense, and hot (I live in Texas), if I run 87 octane during the summer. It goes away if I run higher octane (I put in 93 octane in it when it's very hot) when it's very humid, otherwise, it doesn't ping with 87 octane. The Vulcan engines tend to ping running 87 octane when it's humid. Check for leaks around the intake and pcv valve hose, as well as the throttle body gaskets. Try doing a Sea Foam fog (c-topic finder), if you suspect carbon build up (another cause for ping).
 

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