Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
Cherokee

Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
Compression is 130-150 psi (cold)
Replaced intake manifold gasket 3 times.
Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
Have swapped ign. module in dist w/ no change.
No idle change with propane or WD40 along carb base or intake edges.
Carb change makes NO diff. (have two vari-jet 2bbls).
Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
no apparent valve 'bounce' on the vac gauge) ... not enough vac to
run EGR, barely enough to run distributor vac. advance .... or most of
the 'topside' vac controlled emission controls are sloooow to react
(driveability). I know I need at least 18"hg. vac to0 make the
emission controls, etc. work ... cant get it.
Brake booster is weak due to low vac. .... clamped vac hose to booster
makes NO difference.
Not enough vacuum to hold proper static level of gasoline in carb bowl
(therefore stalls at hard left turn). Float valve NOT sticking, etc.
All vacuum rubber lines and devices intact without leaks (?) .... can
clamp down with pliers on lines without engine stutter (except pcv and
carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
1/2" addtl. vacuum.
The intake manifold isnt warped ( I've checked it 3 times now ... when
replacing intake manifold gaskets.)
Have not had good vacuum since I replaced with this engine.

(Anyone know if there should be an vac. orfice plate between PCV ( and
carb. bowl) and intake manifold) What would be the volumetric vac.
flow for the PCV ?

I'm totally out of ideas.
Engine vac. is so low that Ive lost control of carb and Im depositing
lots of carbon in the combustion chambers, fuel economy is off by 5-6
mpg.

Thanks for ANY input.

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

"Rich Hampel" <RhmpL33@nospam.net> wrote in message
news:141220032235242637%RhmpL33@nospam.net...
> I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
> Cherokee
>
> Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
> Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
> Compression is 130-150 psi (cold)
> Replaced intake manifold gasket 3 times.
> Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
> Have swapped ign. module in dist w/ no change.
> No idle change with propane or WD40 along carb base or intake edges.
> Carb change makes NO diff. (have two vari-jet 2bbls).
> Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
> no apparent valve 'bounce' on the vac gauge) ... not enough vac to
> run EGR, barely enough to run distributor vac. advance .... or most of
> the 'topside' vac controlled emission controls are sloooow to react
> (driveability). I know I need at least 18"hg. vac to0 make the
> emission controls, etc. work ... cant get it.
> Brake booster is weak due to low vac. .... clamped vac hose to booster
> makes NO difference.
> Not enough vacuum to hold proper static level of gasoline in carb bowl
> (therefore stalls at hard left turn). Float valve NOT sticking, etc.
> All vacuum rubber lines and devices intact without leaks (?) .... can
> clamp down with pliers on lines without engine stutter (except pcv and
> carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
> 1/2" addtl. vacuum.
> The intake manifold isnt warped ( I've checked it 3 times now ... when
> replacing intake manifold gaskets.)
> Have not had good vacuum since I replaced with this engine.
>
> (Anyone know if there should be an vac. orfice plate between PCV ( and
> carb. bowl) and intake manifold) What would be the volumetric vac.
> flow for the PCV ?
>
> I'm totally out of ideas.
> Engine vac. is so low that Ive lost control of carb and Im depositing
> lots of carbon in the combustion chambers, fuel economy is off by 5-6
> mpg.
>
> Thanks for ANY input.

This usually indicates some type of restriction in the exhaust system. I
would check the converter and also make sure the muffler hasn't come apart
inside.

Chris

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

"Rich Hampel" <RhmpL33@nospam.net> wrote in message
news:141220032235242637%RhmpL33@nospam.net...
> I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
> Cherokee
>
> Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
> Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
> Compression is 130-150 psi (cold)
> Replaced intake manifold gasket 3 times.
> Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
> Have swapped ign. module in dist w/ no change.
> No idle change with propane or WD40 along carb base or intake edges.
> Carb change makes NO diff. (have two vari-jet 2bbls).
> Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
> no apparent valve 'bounce' on the vac gauge) ... not enough vac to
> run EGR, barely enough to run distributor vac. advance .... or most of
> the 'topside' vac controlled emission controls are sloooow to react
> (driveability). I know I need at least 18"hg. vac to0 make the
> emission controls, etc. work ... cant get it.
> Brake booster is weak due to low vac. .... clamped vac hose to booster
> makes NO difference.
> Not enough vacuum to hold proper static level of gasoline in carb bowl
> (therefore stalls at hard left turn). Float valve NOT sticking, etc.
> All vacuum rubber lines and devices intact without leaks (?) .... can
> clamp down with pliers on lines without engine stutter (except pcv and
> carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
> 1/2" addtl. vacuum.
> The intake manifold isnt warped ( I've checked it 3 times now ... when
> replacing intake manifold gaskets.)
> Have not had good vacuum since I replaced with this engine.
>
> (Anyone know if there should be an vac. orfice plate between PCV ( and
> carb. bowl) and intake manifold) What would be the volumetric vac.
> flow for the PCV ?
>
> I'm totally out of ideas.
> Engine vac. is so low that Ive lost control of carb and Im depositing
> lots of carbon in the combustion chambers, fuel economy is off by 5-6
> mpg.
>
> Thanks for ANY input.

This usually indicates some type of restriction in the exhaust system. I
would check the converter and also make sure the muffler hasn't come apart
inside.

Chris

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

"Rich Hampel" <RhmpL33@nospam.net> wrote in message
news:141220032235242637%RhmpL33@nospam.net...
> I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
> Cherokee
>
> Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
> Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
> Compression is 130-150 psi (cold)
> Replaced intake manifold gasket 3 times.
> Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
> Have swapped ign. module in dist w/ no change.
> No idle change with propane or WD40 along carb base or intake edges.
> Carb change makes NO diff. (have two vari-jet 2bbls).
> Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
> no apparent valve 'bounce' on the vac gauge) ... not enough vac to
> run EGR, barely enough to run distributor vac. advance .... or most of
> the 'topside' vac controlled emission controls are sloooow to react
> (driveability). I know I need at least 18"hg. vac to0 make the
> emission controls, etc. work ... cant get it.
> Brake booster is weak due to low vac. .... clamped vac hose to booster
> makes NO difference.
> Not enough vacuum to hold proper static level of gasoline in carb bowl
> (therefore stalls at hard left turn). Float valve NOT sticking, etc.
> All vacuum rubber lines and devices intact without leaks (?) .... can
> clamp down with pliers on lines without engine stutter (except pcv and
> carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
> 1/2" addtl. vacuum.
> The intake manifold isnt warped ( I've checked it 3 times now ... when
> replacing intake manifold gaskets.)
> Have not had good vacuum since I replaced with this engine.
>
> (Anyone know if there should be an vac. orfice plate between PCV ( and
> carb. bowl) and intake manifold) What would be the volumetric vac.
> flow for the PCV ?
>
> I'm totally out of ideas.
> Engine vac. is so low that Ive lost control of carb and Im depositing
> lots of carbon in the combustion chambers, fuel economy is off by 5-6
> mpg.
>
> Thanks for ANY input.

This usually indicates some type of restriction in the exhaust system. I
would check the converter and also make sure the muffler hasn't come apart
inside.

Chris

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

Hi Rich,
Thirteen, fourteen inches of mercury sounds OK to me, the best
engine with normal valve timing will only get fifteen, before leaning it
out to SMOG specs. The Exhaust Gas Recycling valve should only open on
deceleration, so it may not open until more than eighteen. The
carburetor float bowl is vented to the canister, from there it is purge
back into the intake manifold. I would readjust the carburetor's float
level, seeing you have trouble on turns.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Rich Hampel wrote:
>
> I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
> Cherokee
>
> Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
> Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
> Compression is 130-150 psi (cold)
> Replaced intake manifold gasket 3 times.
> Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
> Have swapped ign. module in dist w/ no change.
> No idle change with propane or WD40 along carb base or intake edges.
> Carb change makes NO diff. (have two vari-jet 2bbls).
> Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
> no apparent valve 'bounce' on the vac gauge) ... not enough vac to
> run EGR, barely enough to run distributor vac. advance .... or most of
> the 'topside' vac controlled emission controls are sloooow to react
> (driveability). I know I need at least 18"hg. vac to0 make the
> emission controls, etc. work ... cant get it.
> Brake booster is weak due to low vac. .... clamped vac hose to booster
> makes NO difference.
> Not enough vacuum to hold proper static level of gasoline in carb bowl
> (therefore stalls at hard left turn). Float valve NOT sticking, etc.
> All vacuum rubber lines and devices intact without leaks (?) .... can
> clamp down with pliers on lines without engine stutter (except pcv and
> carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
> 1/2" addtl. vacuum.
> The intake manifold isnt warped ( I've checked it 3 times now ... when
> replacing intake manifold gaskets.)
> Have not had good vacuum since I replaced with this engine.
>
> (Anyone know if there should be an vac. orfice plate between PCV ( and
> carb. bowl) and intake manifold) What would be the volumetric vac.
> flow for the PCV ?
>
> I'm totally out of ideas.
> Engine vac. is so low that Ive lost control of carb and Im depositing
> lots of carbon in the combustion chambers, fuel economy is off by 5-6
> mpg.
>
> Thanks for ANY input.

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

Hi Rich,
Thirteen, fourteen inches of mercury sounds OK to me, the best
engine with normal valve timing will only get fifteen, before leaning it
out to SMOG specs. The Exhaust Gas Recycling valve should only open on
deceleration, so it may not open until more than eighteen. The
carburetor float bowl is vented to the canister, from there it is purge
back into the intake manifold. I would readjust the carburetor's float
level, seeing you have trouble on turns.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Rich Hampel wrote:
>
> I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
> Cherokee
>
> Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
> Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
> Compression is 130-150 psi (cold)
> Replaced intake manifold gasket 3 times.
> Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
> Have swapped ign. module in dist w/ no change.
> No idle change with propane or WD40 along carb base or intake edges.
> Carb change makes NO diff. (have two vari-jet 2bbls).
> Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
> no apparent valve 'bounce' on the vac gauge) ... not enough vac to
> run EGR, barely enough to run distributor vac. advance .... or most of
> the 'topside' vac controlled emission controls are sloooow to react
> (driveability). I know I need at least 18"hg. vac to0 make the
> emission controls, etc. work ... cant get it.
> Brake booster is weak due to low vac. .... clamped vac hose to booster
> makes NO difference.
> Not enough vacuum to hold proper static level of gasoline in carb bowl
> (therefore stalls at hard left turn). Float valve NOT sticking, etc.
> All vacuum rubber lines and devices intact without leaks (?) .... can
> clamp down with pliers on lines without engine stutter (except pcv and
> carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
> 1/2" addtl. vacuum.
> The intake manifold isnt warped ( I've checked it 3 times now ... when
> replacing intake manifold gaskets.)
> Have not had good vacuum since I replaced with this engine.
>
> (Anyone know if there should be an vac. orfice plate between PCV ( and
> carb. bowl) and intake manifold) What would be the volumetric vac.
> flow for the PCV ?
>
> I'm totally out of ideas.
> Engine vac. is so low that Ive lost control of carb and Im depositing
> lots of carbon in the combustion chambers, fuel economy is off by 5-6
> mpg.
>
> Thanks for ANY input.

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

Hi Rich,
Thirteen, fourteen inches of mercury sounds OK to me, the best
engine with normal valve timing will only get fifteen, before leaning it
out to SMOG specs. The Exhaust Gas Recycling valve should only open on
deceleration, so it may not open until more than eighteen. The
carburetor float bowl is vented to the canister, from there it is purge
back into the intake manifold. I would readjust the carburetor's float
level, seeing you have trouble on turns.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Rich Hampel wrote:
>
> I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
> Cherokee
>
> Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
> Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
> Compression is 130-150 psi (cold)
> Replaced intake manifold gasket 3 times.
> Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
> Have swapped ign. module in dist w/ no change.
> No idle change with propane or WD40 along carb base or intake edges.
> Carb change makes NO diff. (have two vari-jet 2bbls).
> Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
> no apparent valve 'bounce' on the vac gauge) ... not enough vac to
> run EGR, barely enough to run distributor vac. advance .... or most of
> the 'topside' vac controlled emission controls are sloooow to react
> (driveability). I know I need at least 18"hg. vac to0 make the
> emission controls, etc. work ... cant get it.
> Brake booster is weak due to low vac. .... clamped vac hose to booster
> makes NO difference.
> Not enough vacuum to hold proper static level of gasoline in carb bowl
> (therefore stalls at hard left turn). Float valve NOT sticking, etc.
> All vacuum rubber lines and devices intact without leaks (?) .... can
> clamp down with pliers on lines without engine stutter (except pcv and
> carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
> 1/2" addtl. vacuum.
> The intake manifold isnt warped ( I've checked it 3 times now ... when
> replacing intake manifold gaskets.)
> Have not had good vacuum since I replaced with this engine.
>
> (Anyone know if there should be an vac. orfice plate between PCV ( and
> carb. bowl) and intake manifold) What would be the volumetric vac.
> flow for the PCV ?
>
> I'm totally out of ideas.
> Engine vac. is so low that Ive lost control of carb and Im depositing
> lots of carbon in the combustion chambers, fuel economy is off by 5-6
> mpg.
>
> Thanks for ANY input.

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

You're still thinking backwards. Vacuum is low because it runs like ----. It
doesn't run like ---- because vacuum is low. You need to find out why it's
running so bad . Is it a 2SE or E2SE carb? Have you checked cam timing?

You're wasting your time changing intake gaskets. If they leak the engine runs
lean. If you're "depositing lots of carbon in the combustion chambers", it's
too rich.

In message <141220032235242637%RhmpL33@nospam.net>, "Rich Hampel" wrote:

>I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
>Cherokee
>
>Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
>Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
>Compression is 130-150 psi (cold)
>Replaced intake manifold gasket 3 times.
>Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
>Have swapped ign. module in dist w/ no change.
>No idle change with propane or WD40 along carb base or intake edges.
>Carb change makes NO diff. (have two vari-jet 2bbls).
>Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
>no apparent valve 'bounce' on the vac gauge) ... not enough vac to
>run EGR, barely enough to run distributor vac. advance .... or most of
>the 'topside' vac controlled emission controls are sloooow to react
>(driveability). I know I need at least 18"hg. vac to0 make the
>emission controls, etc. work ... cant get it.
>Brake booster is weak due to low vac. .... clamped vac hose to booster
>makes NO difference.
>Not enough vacuum to hold proper static level of gasoline in carb bowl
>(therefore stalls at hard left turn). Float valve NOT sticking, etc.
>All vacuum rubber lines and devices intact without leaks (?) .... can
>clamp down with pliers on lines without engine stutter (except pcv and
>carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
>1/2" addtl. vacuum.
>The intake manifold isnt warped ( I've checked it 3 times now ... when
>replacing intake manifold gaskets.)
>Have not had good vacuum since I replaced with this engine.
>
>(Anyone know if there should be an vac. orfice plate between PCV ( and
>carb. bowl) and intake manifold) What would be the volumetric vac.
>flow for the PCV ?
>
>I'm totally out of ideas.
>Engine vac. is so low that Ive lost control of carb and Im depositing
>lots of carbon in the combustion chambers, fuel economy is off by 5-6
>mpg.
>
>Thanks for ANY input.

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

You're still thinking backwards. Vacuum is low because it runs like ----. It
doesn't run like ---- because vacuum is low. You need to find out why it's
running so bad . Is it a 2SE or E2SE carb? Have you checked cam timing?

You're wasting your time changing intake gaskets. If they leak the engine runs
lean. If you're "depositing lots of carbon in the combustion chambers", it's
too rich.

In message <141220032235242637%RhmpL33@nospam.net>, "Rich Hampel" wrote:

>I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
>Cherokee
>
>Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
>Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
>Compression is 130-150 psi (cold)
>Replaced intake manifold gasket 3 times.
>Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
>Have swapped ign. module in dist w/ no change.
>No idle change with propane or WD40 along carb base or intake edges.
>Carb change makes NO diff. (have two vari-jet 2bbls).
>Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
>no apparent valve 'bounce' on the vac gauge) ... not enough vac to
>run EGR, barely enough to run distributor vac. advance .... or most of
>the 'topside' vac controlled emission controls are sloooow to react
>(driveability). I know I need at least 18"hg. vac to0 make the
>emission controls, etc. work ... cant get it.
>Brake booster is weak due to low vac. .... clamped vac hose to booster
>makes NO difference.
>Not enough vacuum to hold proper static level of gasoline in carb bowl
>(therefore stalls at hard left turn). Float valve NOT sticking, etc.
>All vacuum rubber lines and devices intact without leaks (?) .... can
>clamp down with pliers on lines without engine stutter (except pcv and
>carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
>1/2" addtl. vacuum.
>The intake manifold isnt warped ( I've checked it 3 times now ... when
>replacing intake manifold gaskets.)
>Have not had good vacuum since I replaced with this engine.
>
>(Anyone know if there should be an vac. orfice plate between PCV ( and
>carb. bowl) and intake manifold) What would be the volumetric vac.
>flow for the PCV ?
>
>I'm totally out of ideas.
>Engine vac. is so low that Ive lost control of carb and Im depositing
>lots of carbon in the combustion chambers, fuel economy is off by 5-6
>mpg.
>
>Thanks for ANY input.

Re: Vacuum pressure on '86 2.8L --- TOTALLY STUMPED
 

You're still thinking backwards. Vacuum is low because it runs like ----. It
doesn't run like ---- because vacuum is low. You need to find out why it's
running so bad . Is it a 2SE or E2SE carb? Have you checked cam timing?

You're wasting your time changing intake gaskets. If they leak the engine runs
lean. If you're "depositing lots of carbon in the combustion chambers", it's
too rich.

In message <141220032235242637%RhmpL33@nospam.net>, "Rich Hampel" wrote:

>I'M TOTALLY STUMPED with the vacuum output on 2.8L GM 6 in an XJ
>Cherokee
>
>Kindly offer opinions on low vacuum output on 2.8L in '86 XJ Cherokee
>Engine has 3000 mi. - was a GM 'Johnson' rebuild' (longblock.)
>Compression is 130-150 psi (cold)
>Replaced intake manifold gasket 3 times.
>Ign. Timing at 12 deg BTDC (centrifugal adv. is full operative).
>Have swapped ign. module in dist w/ no change.
>No idle change with propane or WD40 along carb base or intake edges.
>Carb change makes NO diff. (have two vari-jet 2bbls).
>Best vacuum I can get at idle is 13-14 in. hg. vac. (steady reading -
>no apparent valve 'bounce' on the vac gauge) ... not enough vac to
>run EGR, barely enough to run distributor vac. advance .... or most of
>the 'topside' vac controlled emission controls are sloooow to react
>(driveability). I know I need at least 18"hg. vac to0 make the
>emission controls, etc. work ... cant get it.
>Brake booster is weak due to low vac. .... clamped vac hose to booster
>makes NO difference.
>Not enough vacuum to hold proper static level of gasoline in carb bowl
>(therefore stalls at hard left turn). Float valve NOT sticking, etc.
>All vacuum rubber lines and devices intact without leaks (?) .... can
>clamp down with pliers on lines without engine stutter (except pcv and
>carb bowl vac line). When PCV / Carb Bowl vac line is pinched only get
>1/2" addtl. vacuum.
>The intake manifold isnt warped ( I've checked it 3 times now ... when
>replacing intake manifold gaskets.)
>Have not had good vacuum since I replaced with this engine.
>
>(Anyone know if there should be an vac. orfice plate between PCV ( and
>carb. bowl) and intake manifold) What would be the volumetric vac.
>flow for the PCV ?
>
>I'm totally out of ideas.
>Engine vac. is so low that Ive lost control of carb and Im depositing
>lots of carbon in the combustion chambers, fuel economy is off by 5-6
>mpg.
>
>Thanks for ANY input.