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Low Manifold Vacuum
"problem" performance continues in a rebuilt 2.8L GM .....
Engine now has 4000 miles on it and still has relatively low manifold vacuum. Vacuum is running 14-15 in hg. at idle and should be a few inches MORE vac. to adequately run all the vacuum controls: Brake booster, heater controls, dist. vacuum advance, *power piston* (2SE carb), etc. I checked and checked for manifold leaks, reset the damn manifold gaskets three times.... etc. Im pretty damn sure the problem is the engine 'mechanicals' . Compression is 130 psig all cylinders Mechanical valve timing has been degreed, and verified OK. Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) and by accurate degreeing + timing light. --- both methods equate to the same EXACT timing advance. NO leaking vacuum hoses or controls. If I remove a vac. hose from the manifold port the engine **increases*** rpm --- which tells me I dont have a leak. Poor vacuum causes power piston in carb to lift 'early' (for over-rich mixture) - if I manually hold power piston / metering rod and remove a manifold vac hose = same rpm increase. Engine was broken in with 20 weight straight weight non-detergent oil. Im about ready to dump a half can of cleanser down the carb to scuff the cylinder walls in desparation and run the valve lifters with ZERO lash ...... Your sage advice would be appreciated. I need another 2-3 inches of vacuum to make all the vac. controls, brake booster and power piston-ed carb. to operate properly. Any advice of why this damn engine is running 'short' by about 2-3 inches hg. of vacuum and what to do about it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. ;-) |
Re: Low Manifold Vacuum
That's not really low for a SMOG motor at idle. You may see that's
at the edge of the green zone: http://www.----------.com/vacuumgauge.jpg And you have noticed it's up around twenty at the more efficient operating Revolutions Per Minute. None of the accessories use vacuum, unless used. God Bless America, ßill O|||||||O mailto:-------------------- Rich Hampel wrote: > > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
That's not really low for a SMOG motor at idle. You may see that's
at the edge of the green zone: http://www.----------.com/vacuumgauge.jpg And you have noticed it's up around twenty at the more efficient operating Revolutions Per Minute. None of the accessories use vacuum, unless used. God Bless America, ßill O|||||||O mailto:-------------------- Rich Hampel wrote: > > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
That's not really low for a SMOG motor at idle. You may see that's
at the edge of the green zone: http://www.----------.com/vacuumgauge.jpg And you have noticed it's up around twenty at the more efficient operating Revolutions Per Minute. None of the accessories use vacuum, unless used. God Bless America, ßill O|||||||O mailto:-------------------- Rich Hampel wrote: > > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
1st up, I'm not familiar with the 2.8, but is it possible you have a leak in
your brake servo ? You say the problem continues in a new engine ? Dave Milne, Scotland '91 Grand Wagoneer, '99 TJ "Rich Hampel" <RhmpL33@nospam.net> wrote in message news:180120051536111216%RhmpL33@nospam.net... > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
1st up, I'm not familiar with the 2.8, but is it possible you have a leak in
your brake servo ? You say the problem continues in a new engine ? Dave Milne, Scotland '91 Grand Wagoneer, '99 TJ "Rich Hampel" <RhmpL33@nospam.net> wrote in message news:180120051536111216%RhmpL33@nospam.net... > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
1st up, I'm not familiar with the 2.8, but is it possible you have a leak in
your brake servo ? You say the problem continues in a new engine ? Dave Milne, Scotland '91 Grand Wagoneer, '99 TJ "Rich Hampel" <RhmpL33@nospam.net> wrote in message news:180120051536111216%RhmpL33@nospam.net... > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
I would guess that your valves are a bit short on time if you don't have
zero lash on them. My book calls for zero. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Rich Hampel wrote: > > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
I would guess that your valves are a bit short on time if you don't have
zero lash on them. My book calls for zero. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Rich Hampel wrote: > > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
Re: Low Manifold Vacuum
I would guess that your valves are a bit short on time if you don't have
zero lash on them. My book calls for zero. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Rich Hampel wrote: > > "problem" performance continues in a rebuilt 2.8L GM ..... > Engine now has 4000 miles on it and still has relatively low manifold > vacuum. Vacuum is running 14-15 in hg. at idle and should be a few > inches MORE vac. to adequately run all the vacuum controls: Brake > booster, heater controls, dist. vacuum advance, *power piston* (2SE > carb), etc. > > I checked and checked for manifold leaks, reset the damn manifold > gaskets three times.... etc. > Im pretty damn sure the problem is the engine 'mechanicals' . > Compression is 130 psig all cylinders > Mechanical valve timing has been degreed, and verified OK. > Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.) > and by accurate degreeing + timing light. --- both methods equate to > the same EXACT timing advance. > NO leaking vacuum hoses or controls. > If I remove a vac. hose from the manifold port the engine > **increases*** rpm --- which tells me I dont have a leak. > Poor vacuum causes power piston in carb to lift 'early' (for over-rich > mixture) - if I manually hold power piston / metering rod and remove a > manifold vac hose = same rpm increase. > > Engine was broken in with 20 weight straight weight non-detergent oil. > > Im about ready to dump a half can of cleanser down the carb to scuff > the cylinder walls in desparation and run the valve lifters with ZERO > lash ...... > > Your sage advice would be appreciated. I need another 2-3 inches of > vacuum to make all the vac. controls, brake booster and power piston-ed > carb. to operate properly. Any advice of why this damn engine is > running 'short' by about 2-3 inches hg. of vacuum and what to do about > it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated. > > ;-) |
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