90 YJ 4.2L random power loss on hills
 

All,

Hope you can help. My 90 YJ with a 4.2 six has just developed a periodic
power loss problem when cruising at highway speeds and having to climb a
slight hill. It seems to happen in 4th gear, RPMs seems to remain steady at
200 RPMs. It seems like it is fuel starved but I really cannot tell.

The Jeep has 143,000 miles. Here is what I have done/checked.

1) New factory distributor about 6 months ago (4K miles ago).
2) Plugs cap and rotor 10 months ago (10K miles ago).
3) Just tested resistance on all ignition wires - all ok.
4) Just put in new fuel filter after problem developed.
5) Tested fuel pump pressure - 7 PSI, with engine cranking (not running -
seems a bit high). Factory service manual calls for 4-5 PSI.
6) Tested fuel pump capacity - 20 ounces in 30 seconds. Factory service
manual says at least 16 ounces.
7) Problem will randomly happen with fuel cap removed.
8) Problem will randomly happen with vacuum hose to EGR valve disconnected
and plugged.
9) Problem will randomly happen with vacuum hose from back of carb to
charcoal canister purge valve disconnected and plugged.
10) 200 miles ago, I rebuilt the carb and set the float level and other
setting to specs. It was running great up until this week.
11) All gauges read normal when it is acting up.
12) Problem does not happen at low speeds around time.
13) About 6 months ago, I recall once or twice experiencing similar symptoms
for a few seconds, but much less noticable. There after never saw it again
until this week (but more severe now).


I am beginning to think that it may be the ignition control module or
possibly a catalytic converter going bad. How long do timing chains last on
the 4.2 six? Do any of you other suggestions?

Thanks.

mpv

Re: 90 YJ 4.2L random power loss on hills
 

Well....

You 'could' be describing a plugged up air filter on the gas tank and
carb float bowl vents, but.....

The gas tank needs an air vent to keep it at atmospheric pressure on the
4.2 engine setup.

The carb float bowl needs the same thing. You plugged the carb vent
with a bolt in step 9, that can cause your symptoms.

Opening the gas cap by itself will override the vent air filter issue
for both though....

Unless you did both at the same time?

Tag me back on that and I will toss some more guesses at you tomorrow.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Michael Vincenty wrote:
>
> All,
>
> Hope you can help. My 90 YJ with a 4.2 six has just developed a periodic
> power loss problem when cruising at highway speeds and having to climb a
> slight hill. It seems to happen in 4th gear, RPMs seems to remain steady at
> 200 RPMs. It seems like it is fuel starved but I really cannot tell.
>
> The Jeep has 143,000 miles. Here is what I have done/checked.
>
> 1) New factory distributor about 6 months ago (4K miles ago).
> 2) Plugs cap and rotor 10 months ago (10K miles ago).
> 3) Just tested resistance on all ignition wires - all ok.
> 4) Just put in new fuel filter after problem developed.
> 5) Tested fuel pump pressure - 7 PSI, with engine cranking (not running -
> seems a bit high). Factory service manual calls for 4-5 PSI.
> 6) Tested fuel pump capacity - 20 ounces in 30 seconds. Factory service
> manual says at least 16 ounces.
> 7) Problem will randomly happen with fuel cap removed.
> 8) Problem will randomly happen with vacuum hose to EGR valve disconnected
> and plugged.
> 9) Problem will randomly happen with vacuum hose from back of carb to
> charcoal canister purge valve disconnected and plugged.
> 10) 200 miles ago, I rebuilt the carb and set the float level and other
> setting to specs. It was running great up until this week.
> 11) All gauges read normal when it is acting up.
> 12) Problem does not happen at low speeds around time.
> 13) About 6 months ago, I recall once or twice experiencing similar symptoms
> for a few seconds, but much less noticable. There after never saw it again
> until this week (but more severe now).
>
> I am beginning to think that it may be the ignition control module or
> possibly a catalytic converter going bad. How long do timing chains last on
> the 4.2 six? Do any of you other suggestions?
>
> Thanks.
>
> mpv

Re: 90 YJ 4.2L random power loss on hills
 

Well....

You 'could' be describing a plugged up air filter on the gas tank and
carb float bowl vents, but.....

The gas tank needs an air vent to keep it at atmospheric pressure on the
4.2 engine setup.

The carb float bowl needs the same thing. You plugged the carb vent
with a bolt in step 9, that can cause your symptoms.

Opening the gas cap by itself will override the vent air filter issue
for both though....

Unless you did both at the same time?

Tag me back on that and I will toss some more guesses at you tomorrow.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Michael Vincenty wrote:
>
> All,
>
> Hope you can help. My 90 YJ with a 4.2 six has just developed a periodic
> power loss problem when cruising at highway speeds and having to climb a
> slight hill. It seems to happen in 4th gear, RPMs seems to remain steady at
> 200 RPMs. It seems like it is fuel starved but I really cannot tell.
>
> The Jeep has 143,000 miles. Here is what I have done/checked.
>
> 1) New factory distributor about 6 months ago (4K miles ago).
> 2) Plugs cap and rotor 10 months ago (10K miles ago).
> 3) Just tested resistance on all ignition wires - all ok.
> 4) Just put in new fuel filter after problem developed.
> 5) Tested fuel pump pressure - 7 PSI, with engine cranking (not running -
> seems a bit high). Factory service manual calls for 4-5 PSI.
> 6) Tested fuel pump capacity - 20 ounces in 30 seconds. Factory service
> manual says at least 16 ounces.
> 7) Problem will randomly happen with fuel cap removed.
> 8) Problem will randomly happen with vacuum hose to EGR valve disconnected
> and plugged.
> 9) Problem will randomly happen with vacuum hose from back of carb to
> charcoal canister purge valve disconnected and plugged.
> 10) 200 miles ago, I rebuilt the carb and set the float level and other
> setting to specs. It was running great up until this week.
> 11) All gauges read normal when it is acting up.
> 12) Problem does not happen at low speeds around time.
> 13) About 6 months ago, I recall once or twice experiencing similar symptoms
> for a few seconds, but much less noticable. There after never saw it again
> until this week (but more severe now).
>
> I am beginning to think that it may be the ignition control module or
> possibly a catalytic converter going bad. How long do timing chains last on
> the 4.2 six? Do any of you other suggestions?
>
> Thanks.
>
> mpv

Re: 90 YJ 4.2L random power loss on hills
 

See my comments imbedded throughout:

"Mike Romain" <romainm@sympatico.ca> wrote in message
news:3F4593B2.5DDADE57@sympatico.ca...
> Well....
>
> You 'could' be describing a plugged up air filter on the gas tank and
> carb float bowl vents, but.....

Do you mean the filter under the charcoal canister when you say "air filter
onj the gas tank"?

Just a note, on the carb float bowl vent, on my rebuild 2 weeks ago, I did
replace the little rubber seal in that carb and make the adjustment so that
it the bowl vent would open upon partial-to-full acceleration.

>
> The gas tank needs an air vent to keep it at atmospheric pressure on the
> 4.2 engine setup.
>
> The carb float bowl needs the same thing. You plugged the carb vent
> with a bolt in step 9, that can cause your symptoms.
>
> Opening the gas cap by itself will override the vent air filter issue
> for both though....
>
> Unless you did both at the same time?
>

Test 7 (removing gas cap) and Test 9 (removing & plugging vac line to
charcoal canister) were performed independently. Once when the problem was
occuring, I pulled over, and physically removed the fuel cap. Soon as I
turned it left, there was that "swoosh" suction sound (indicating negative
air pressure in the gas tank). I drove on without the gas cap and still was
experiencing the problem. Later I removed & plugging vac line to charcoal
canister with the gas cap attached.


> Tag me back on that and I will toss some more guesses at you tomorrow.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> Michael Vincenty wrote:
> >
> > All,
> >
> > Hope you can help. My 90 YJ with a 4.2 six has just developed a
periodic
> > power loss problem when cruising at highway speeds and having to climb a
> > slight hill. It seems to happen in 4th gear, RPMs seems to remain
steady at
> > 200 RPMs. It seems like it is fuel starved but I really cannot tell.
> >
> > The Jeep has 143,000 miles. Here is what I have done/checked.
> >
> > 1) New factory distributor about 6 months ago (4K miles ago).
> > 2) Plugs cap and rotor 10 months ago (10K miles ago).
> > 3) Just tested resistance on all ignition wires - all ok.
> > 4) Just put in new fuel filter after problem developed.
> > 5) Tested fuel pump pressure - 7 PSI, with engine cranking (not
running -
> > seems a bit high). Factory service manual calls for 4-5 PSI.
> > 6) Tested fuel pump capacity - 20 ounces in 30 seconds. Factory service
> > manual says at least 16 ounces.
> > 7) Problem will randomly happen with fuel cap removed.
> > 8) Problem will randomly happen with vacuum hose to EGR valve
disconnected
> > and plugged.
> > 9) Problem will randomly happen with vacuum hose from back of carb to
> > charcoal canister purge valve disconnected and plugged.
> > 10) 200 miles ago, I rebuilt the carb and set the float level and other
> > setting to specs. It was running great up until this week.
> > 11) All gauges read normal when it is acting up.
> > 12) Problem does not happen at low speeds around time.
> > 13) About 6 months ago, I recall once or twice experiencing similar
symptoms
> > for a few seconds, but much less noticable. There after never saw it
again
> > until this week (but more severe now).
> >
> > I am beginning to think that it may be the ignition control module or
> > possibly a catalytic converter going bad. How long do timing chains
last on
> > the 4.2 six? Do any of you other suggestions?
> >
> > Thanks.
> >
> > mpv

Re: 90 YJ 4.2L random power loss on hills
 

See my comments imbedded throughout:

"Mike Romain" <romainm@sympatico.ca> wrote in message
news:3F4593B2.5DDADE57@sympatico.ca...
> Well....
>
> You 'could' be describing a plugged up air filter on the gas tank and
> carb float bowl vents, but.....

Do you mean the filter under the charcoal canister when you say "air filter
onj the gas tank"?

Just a note, on the carb float bowl vent, on my rebuild 2 weeks ago, I did
replace the little rubber seal in that carb and make the adjustment so that
it the bowl vent would open upon partial-to-full acceleration.

>
> The gas tank needs an air vent to keep it at atmospheric pressure on the
> 4.2 engine setup.
>
> The carb float bowl needs the same thing. You plugged the carb vent
> with a bolt in step 9, that can cause your symptoms.
>
> Opening the gas cap by itself will override the vent air filter issue
> for both though....
>
> Unless you did both at the same time?
>

Test 7 (removing gas cap) and Test 9 (removing & plugging vac line to
charcoal canister) were performed independently. Once when the problem was
occuring, I pulled over, and physically removed the fuel cap. Soon as I
turned it left, there was that "swoosh" suction sound (indicating negative
air pressure in the gas tank). I drove on without the gas cap and still was
experiencing the problem. Later I removed & plugging vac line to charcoal
canister with the gas cap attached.


> Tag me back on that and I will toss some more guesses at you tomorrow.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> Michael Vincenty wrote:
> >
> > All,
> >
> > Hope you can help. My 90 YJ with a 4.2 six has just developed a
periodic
> > power loss problem when cruising at highway speeds and having to climb a
> > slight hill. It seems to happen in 4th gear, RPMs seems to remain
steady at
> > 200 RPMs. It seems like it is fuel starved but I really cannot tell.
> >
> > The Jeep has 143,000 miles. Here is what I have done/checked.
> >
> > 1) New factory distributor about 6 months ago (4K miles ago).
> > 2) Plugs cap and rotor 10 months ago (10K miles ago).
> > 3) Just tested resistance on all ignition wires - all ok.
> > 4) Just put in new fuel filter after problem developed.
> > 5) Tested fuel pump pressure - 7 PSI, with engine cranking (not
running -
> > seems a bit high). Factory service manual calls for 4-5 PSI.
> > 6) Tested fuel pump capacity - 20 ounces in 30 seconds. Factory service
> > manual says at least 16 ounces.
> > 7) Problem will randomly happen with fuel cap removed.
> > 8) Problem will randomly happen with vacuum hose to EGR valve
disconnected
> > and plugged.
> > 9) Problem will randomly happen with vacuum hose from back of carb to
> > charcoal canister purge valve disconnected and plugged.
> > 10) 200 miles ago, I rebuilt the carb and set the float level and other
> > setting to specs. It was running great up until this week.
> > 11) All gauges read normal when it is acting up.
> > 12) Problem does not happen at low speeds around time.
> > 13) About 6 months ago, I recall once or twice experiencing similar
symptoms
> > for a few seconds, but much less noticable. There after never saw it
again
> > until this week (but more severe now).
> >
> > I am beginning to think that it may be the ignition control module or
> > possibly a catalytic converter going bad. How long do timing chains
last on
> > the 4.2 six? Do any of you other suggestions?
> >
> > Thanks.
> >
> > mpv

Re: 90 YJ 4.2L random power loss on hills
 

"Michael Vincenty" <mvincenty@adelphia.net> wrote in message
news:p8e1b.5677$Nc.3544698@news1.news.adelphia.net ...
> All,
>
> Hope you can help. My 90 YJ with a 4.2 six has just developed a periodic
> power loss problem when cruising at highway speeds and having to climb a
> slight hill. It seems to happen in 4th gear, RPMs seems to remain steady
at
> 200 RPMs. It seems like it is fuel starved but I really cannot tell.

You probably mean 2000.

No problem on the flats? At higher speeds? I'd guess you have too much
fuel in your float bowl... either a stuck/bad needle and seat, or adjustment
needed on the float height. Does it bog, or backfire/pop? If it leans out,
you should get backfire; my bet is rich. Look for black smoke from the
tailpipe in failure mode.
__
Steve
..

Re: 90 YJ 4.2L random power loss on hills
 

"Michael Vincenty" <mvincenty@adelphia.net> wrote in message
news:p8e1b.5677$Nc.3544698@news1.news.adelphia.net ...
> All,
>
> Hope you can help. My 90 YJ with a 4.2 six has just developed a periodic
> power loss problem when cruising at highway speeds and having to climb a
> slight hill. It seems to happen in 4th gear, RPMs seems to remain steady
at
> 200 RPMs. It seems like it is fuel starved but I really cannot tell.

You probably mean 2000.

No problem on the flats? At higher speeds? I'd guess you have too much
fuel in your float bowl... either a stuck/bad needle and seat, or adjustment
needed on the float height. Does it bog, or backfire/pop? If it leans out,
you should get backfire; my bet is rich. Look for black smoke from the
tailpipe in failure mode.
__
Steve
..

Re: 90 YJ 4.2L random power loss on hills
 

Make sure there are no bad vac lines...I'd replace every one under the hood.
Check around the base of the carb for leaks too. Make sure the EGR valve is
working properly. The canister is probably bad too with all the miles on your
rig. You can bypass this.....My state does not have inspections so I gotta way
with it....you may not. You can find them in salvage yards or thru Jeep for
about $90 or more depending on how greedy your dealer is. After all this
re-check timming and adjust up until you get max performance without PING.

Also....I highly advise you to do the "Nutter Bypass" and replace the stock
distributor cap with one from a 84 Ford F150 300 6cyl. This will prevent cross
fire at higher RPM's.

I had the same problems you did and after all this work I can pull hills at
highway speed with ease....even while towing my jetski. Gas mileage increased
also.

Brian
88 YJ

Re: 90 YJ 4.2L random power loss on hills
 

Make sure there are no bad vac lines...I'd replace every one under the hood.
Check around the base of the carb for leaks too. Make sure the EGR valve is
working properly. The canister is probably bad too with all the miles on your
rig. You can bypass this.....My state does not have inspections so I gotta way
with it....you may not. You can find them in salvage yards or thru Jeep for
about $90 or more depending on how greedy your dealer is. After all this
re-check timming and adjust up until you get max performance without PING.

Also....I highly advise you to do the "Nutter Bypass" and replace the stock
distributor cap with one from a 84 Ford F150 300 6cyl. This will prevent cross
fire at higher RPM's.

I had the same problems you did and after all this work I can pull hills at
highway speed with ease....even while towing my jetski. Gas mileage increased
also.

Brian
88 YJ

Re: 90 YJ 4.2L random power loss on hills
 

Steve,

I think that you are onto something with the float level. I do notice it
bogs down and seems to choke out the exhaust. It seems much more prominent
on long hill climbs at high speeds. Maybe this is suggesting that the float
level is mis-adjusted and causing the carb to really lean out. I really
thought that I had the float adjusted properly when I rebuilt it in early
Aug. However, last weekend (after the rebuild), I noticed that the fuel
line where it attached to the carb was leaking, I tightened it up, both
line and the brass fitting which goes into the carb (the brass fitting which
holds the float needle valve). Now I am wondering if by tightening up the
brass fitting, did this through off the float level enough to cause this
problem (I never noticed this bogging problem until after I tightened up the
brass fitting).

What do you all think? And thanks much for your time.

mpv


"Steve Cowell" <scowell@sbcglobal.net> wrote in message
news:3cn1b.2996$oJ2.49@newssvr22.news.prodigy.com. ..
>
> "Michael Vincenty" <mvincenty@adelphia.net> wrote in message
> news:p8e1b.5677$Nc.3544698@news1.news.adelphia.net ...
> > All,
> >
> > Hope you can help. My 90 YJ with a 4.2 six has just developed a
periodic
> > power loss problem when cruising at highway speeds and having to climb a
> > slight hill. It seems to happen in 4th gear, RPMs seems to remain
steady
> at
> > 200 RPMs. It seems like it is fuel starved but I really cannot tell.
>
> You probably mean 2000.
>
> No problem on the flats? At higher speeds? I'd guess you have too much
> fuel in your float bowl... either a stuck/bad needle and seat, or
adjustment
> needed on the float height. Does it bog, or backfire/pop? If it leans
out,
> you should get backfire; my bet is rich. Look for black smoke from the
> tailpipe in failure mode.
> __
> Steve
> .
>
>