Reading Spark Plugs
Lead Driver
Joined: Jan 2019
Posts: 5,086
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From: N.W. Alabama
Wasnt saying to check timing, was saying that you can watch timing change, if you leave spout plugged in, if timing doesnt, move around, with spout plugged in, then your PCM, could be bad, or when you plugged the 60 pin connector in it may have pushed a pin or pins, and not getting good connection, even with the injectors cleaned, those 2 could be why, your pressure leaks down within one minute of turning it off, if the rest look like the other 2
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Cross-Country
Joined: Dec 2023
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You say this was a propane fueled truck when you got it? Have you changed the PCM? I'm not sure how they did these conversions WRT the PCM but a regular computer for gasoline won't work( runs too lean) so they either had to install a chip or swap in a custom propane spec PCM to fatten up the mixture. If you haven't been in there yet you should probably pull the PCM out for a look and if there is a chip on it pull it off.
Aussie 1990 5.8 EFI with C6 and 2WD.
Cargo Master
Joined: Oct 2020
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Cams can be ground to improve performance in engines that are going to be run on gaseous fuels, propane, natural gas etc. Most of the time what is done is to cut back on the duration especially on the exhaust side and tighten up the lobe separation. These things are done because unlike liquid fuel the gas takes up a significant amount of volume in the intake tract and this reduces the volumetric efficiency of the engine. This is what causes it to have reduced torque and horsepower and a high EGT when compared to when it is run on gasoline.
Engines built specifically for running on propane or natural gas are often built with much higher compression ratios than ones that are run on pump gas and this is done to get performance up and the EGT down. None of this would work against you when it comes to fuel economy.
Engines built specifically for running on propane or natural gas are often built with much higher compression ratios than ones that are run on pump gas and this is done to get performance up and the EGT down. None of this would work against you when it comes to fuel economy.
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Cross-Country
Joined: Dec 2023
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Thanks for your reply Dave, I really appreciate the knowledge. It's one more thing to strike off the list of potential causes for my issues.
I searched online for info on LPG cams, but didn't really find too much. I did come across info regarding exhaust, which you also succinctly explained. The technology has really been dropped here in Australia, in fact you can barely find stations that supply it any more.
Maybe I'm grasping at straws trying to work out my mileage issue! My truck seems to run well, just the mileage to me indicates something is not right, and that annoys me.
I searched online for info on LPG cams, but didn't really find too much. I did come across info regarding exhaust, which you also succinctly explained. The technology has really been dropped here in Australia, in fact you can barely find stations that supply it any more.
Maybe I'm grasping at straws trying to work out my mileage issue! My truck seems to run well, just the mileage to me indicates something is not right, and that annoys me.
Cargo Master
Joined: Oct 2020
Posts: 2,710
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A friend of mine who worked at Reed Cams for many years told me that they used to grind a lot of cams for some companies that would convert gasoline engines usually Olds 350s, 454 Chevrolet and 460 Ford to run on natural gas. I don't know if they were used as irrigation engines or for some other purpose but some of them were run at moderate rpm 24 hours a day for a long time and working with the camshaft timing and other aspects of the engine build made a big difference in the overall reliability.
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