Gas Problems

[Steve L]

I just moved down here to lower altitude in Yuma, Az but I am having problems with finding high enough octane fuel to keep my LS-1 happy. The highest pump rating I can find anywhere around here is 91 and my T/A does not digest this well at the lower altitude (91 was fine around Denver). The owner's manual calls for 93 and when it is available, that is what I have used.

Some locals have suggested AvGas or MoGas but I don't know the pro/cons of either of those. The store-bought octane boost does quiet the pinging some, but not all together, and that will eventually get quite pricey along with gumming things up...won't it?

The engine internals are still stock, so I am still carrying the stock 10.1:1 compression ratio. I have opened up the intake and exhaust as well as installed the Hypertech Power Programmer, but none of those should necessitate the use of higher octane fuel. I took off the Hypertech to see if the computer would adjust on its own, but I still have the same problem.

Suggestions anyone?

[Matt Leicester]

I assume you're hearing preignition or detonation? The normal causes for such nonsense are :
too low octane (what you're trying to fix);
too much ignition advance;
fuel/air mixture too lean.

If you can adjust mixture in different conditions, try richening it up a bit where you hear the knock. If you can't isolate distinct conditions, you may try raising your fuel pressure a tick. The amount of fuel injected is a product of injector pulse width (duration of opening) and fuel pressure - the computer only knows pulse width, so more fuel pressure will richen the mixture across the board.

I would guess with a car as new as yours that the ignition timing is pretty much controlled by the computer as well. Sometimes you can adjust the crankshaft angle sensor or cam angle sensor to advance or retard spark, sometimes the computer needs to be reflashed. You want to retard your ignition to lower combustion chamber temps enough to eliminate detonation.

If your problems are at part throttle and full throttle seems to be fine, you may also check the EGR system. EGR's mission in life is to lower combustion temps, so if it doesn't work you can get part throttle knock. At full throttle, most EGR systems don't do anything.

Octane boosters are basically best avoided. When they say on the ridiculously expensive bottle "raises octane rating 6 points", they are talking from 91.0 to 91.6, not 91 to 97. Also, and I haven't used octane boosters since the Hotruck had an actual motor, boosters work (or at least worked) by slowing the rate of burn of the flame front, not by raising the flash point of the fuel. Translated, that means that the mixture starts burning at close to the same temperature but burns much slower. In other words, they kill horsepower! You want the gas to have a higher ignition temperature to eliminate detonation, but as long as the flame front does not start before it should (like when the spark plugs fires...), you want the mixture to burn very quickly to make good power.

Even 100 octane LL avgas is Low Lead, not unleaded, not a good idea. Not to mention that avgas is typically formulated to work at high altitudes and low temperatures, and that pretty much leaves Arizona out on both counts. You should be able to find 100 octane unleaded race gas around, which would be a great cure if you can afford it, but figure on $5-$7.00 a gallon if you find it at all. Feel free to mix the race gas and 91 octane unleaded to get the octane you need at reduced expense from straight 100 octane, just try to be consistant on your percentages.

Keep in mind when reading this that I pretty much live, eat and breathe two strokes these days, and I freely admit to the possibility that I am waaaaay off base. I just didn't want you to think all of RMSolo was ignoring you since you left!;)

Matt Leicester

[LoCore]

Great writeup Matt. I'm pretty clueless when it comes to this stuff, but had a story to share that has a remote chance of being related.

When I moved to Colorado I had a then-new 1989 Pontiac Grand Prix I bought in Iowa while still in college. One of the first services done under warranty here was to reprogram (chip?) the ECU to deal with the altitude; the car had been running rather poorly out here.

Are newer cars still prone to needing different software to run normally at this altitude? Or are the ECUs and fuel system smart enough now to work out how to deal with the changing altitudes.

The newer ECUs "learn" their settings now, don't they? If so, could it be that Steve's car thinks it is still in Colorado? Could a solution be as simply as an ECU reset?

[aleliaert]

Perhaps there are come carbon deposits in the engine contributing to the problem? I don't know about the LS1 but some engines are notorious for ping-inducing carbon buildup.

A can of BG44k might be worth a try. It works like a charm on our 1.8 turbo Passat, which is very demanding in terms of fluids/maintenance.

[00 SS]

Steve,

The BG 44K is a good idea to try. I doubt you have excessive built up of carbon, but cleaning thingfs is never a bad idea. Second, the LS1 is equiped with knock sensors that are supposed to retard the timing when knock is detected. You may have bad sensors. Have the computer scanned to see if you have any knock retard (KR). If the scan shows no KR and it is knocking, then the sesors have gone out. Matt's explination is a good one, but amny of his suggestions ae not something you can adjust without a tuning program like LS1edit and a laptop on your car. Find a good speed shop and they should be able to help you read the computer. KR will not set an SES light and will not show up with a normal trouble code reader, you need to read the entire computer. One less expensive program you could by to read the computer with is Autotap, but it's still over $200. If you are in the Phoenix area sometime soon check out Arizona Speed and Marine. They are a great speed shop and should be able to fix you up.

[Warrtalon]

You probably need a retune, if that's possible. I'm not sure how your chip works.

You can also try to find a place that sells unleaded race gas (98/100/104), and keep a big 5-gal jug of it, then be sure to add a gallon or 2 to each fillup of 91. I already do that here in CO due to the 91 and being used to 93 with all the boost I run on a daily basis.

[Captain_Solo]

Try this:
http://re3.mm-a2.yimg.com/image/404751550

sorry, couldn't resist...I hope it all works out.

[lewsthomas]

What up Devil Dog..

I actually had the same issue when I was posted in Nevada with a 95 Mustang GT that had guess what, a Hyper-Tech Power Program.'

My only Fix was I ditched the Hyper Tech.

Not much help but funny that I had the same problem almost.

Later Chief.

Lew