Fuel pressure regulator?
03-15-2012, 08:03 PM
#1
Member
Thread Starter
Join Date: Jan 2012
Location: Camdenton, Mo
Posts: 231
Likes: 0
Received 0 Likes
on
0 Posts
Year: 94
Model: Cherokee
Engine: 4.0
Fuel pressure regulator?
My 94 cranks for awhile before it starts so I tested the fpr. With the vacuum hooked up it idles at ~31 psi, unhooked ~41. With its hooked up it fluctuates when revved to ~41, unhooked it is steady. I assume I need to replace it? Or could it be a different problem?
03-15-2012, 08:12 PM
#2
CF Veteran
Join Date: Aug 2011
Location: Nor-Cal Coast
Posts: 10,489
Likes: 0
Received 17 Likes
on
17 Posts
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Your pressure and regulator are OK. Maybe fuel pressure is bleeding off, maybe the check valve in the pump.
Try turning the ign on a sec, then off a few times first and see if that helps.
Try turning the ign on a sec, then off a few times first and see if that helps.
03-15-2012, 10:10 PM
#6
CF Veteran
Join Date: Nov 2011
Location: phoenix az
Posts: 1,290
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0l 6 cylinder
Originally Posted by DFlintstone
Your pressure and regulator are OK. Maybe fuel pressure is bleeding off, maybe the check valve in the pump.
Try turning the ign on a sec, then off a few times first and see if that helps.
Try turning the ign on a sec, then off a few times first and see if that helps.
03-15-2012, 10:41 PM
#7
Member
Thread Starter
Join Date: Jan 2012
Location: Camdenton, Mo
Posts: 231
Likes: 0
Received 0 Likes
on
0 Posts
Year: 94
Model: Cherokee
Engine: 4.0
I turn the key twice and it gets up to 10 psi. Still seem slow to start but not as bad. Holds 31 at idle. Shut it off and its back to zero. Bad injector?
Trending Topics
03-15-2012, 10:42 PM
#8
CF Veteran
Join Date: Nov 2011
Location: phoenix az
Posts: 1,290
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0l 6 cylinder
Originally Posted by 944.0
I turn the key twice and it gets up to 10 psi. Still seem slow to start but not as bad. Holds 31 at idle. Shut it off and its back to zero. Bad injector?
03-15-2012, 11:01 PM
#10
CF Veteran
Join Date: Aug 2011
Location: Nor-Cal Coast
Posts: 10,489
Likes: 0
Received 17 Likes
on
17 Posts
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Sometimes I think Steve is working on his post count. No there is only one regulator and I think yours is fine. I have it that the pressure went up in 96 with OBD II. http://www.jeep4.0performance.4mg.com/tech_specs.html
The "prime" suspect, (ha, ha), is the check valve in the fuel pump. Might be it should not let the pressure drop more than 20 Lbs in 1/2 an hour. Also an injector could leak as well as the regulator, but the check valve is what get's talked about. So...cycleing the key, it never goes over 10?
The "prime" suspect, (ha, ha), is the check valve in the fuel pump. Might be it should not let the pressure drop more than 20 Lbs in 1/2 an hour. Also an injector could leak as well as the regulator, but the check valve is what get's talked about. So...cycleing the key, it never goes over 10?
03-15-2012, 11:10 PM
#11
Member
Thread Starter
Join Date: Jan 2012
Location: Camdenton, Mo
Posts: 231
Likes: 0
Received 0 Likes
on
0 Posts
Year: 94
Model: Cherokee
Engine: 4.0
The pump will only run for the first two key cycles. 10 is as high as it goes when cycling the key. Also the oil smells pretty strongly of gas.
03-15-2012, 11:17 PM
#12
CF Veteran
Join Date: Aug 2011
Location: Nor-Cal Coast
Posts: 10,489
Likes: 0
Received 17 Likes
on
17 Posts
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Really. I haven't done it, but guys have posted that they removed their fuel rail with the injectors on it an messed around looking at flow and for leaking. Certainly something to do with caution, maybe not in the garage so you don't loose the house too!
03-15-2012, 11:19 PM
#13
CF Veteran
Join Date: Nov 2011
Location: phoenix az
Posts: 1,290
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0l 6 cylinder
Originally Posted by DFlintstone
Sometimes I think Steve is working on his post count. No there is only one regulator and I think yours is fine. I have it that the pressure went up in 96 with OBD II. http://www.jeep4.0performance.4mg.com/tech_specs.html
The "prime" suspect, (ha, ha), is the check valve in the fuel pump. Might be it should not let the pressure drop more than 20 Lbs in 1/2 an hour. Also an injector could leak as well as the regulator, but the check valve is what get's talked about. So...cycleing the key, it never goes over 10?
The "prime" suspect, (ha, ha), is the check valve in the fuel pump. Might be it should not let the pressure drop more than 20 Lbs in 1/2 an hour. Also an injector could leak as well as the regulator, but the check valve is what get's talked about. So...cycleing the key, it never goes over 10?
03-15-2012, 11:26 PM
#14
Member
Thread Starter
Join Date: Jan 2012
Location: Camdenton, Mo
Posts: 231
Likes: 0
Received 0 Likes
on
0 Posts
Year: 94
Model: Cherokee
Engine: 4.0
Originally Posted by DFlintstone
Sometimes I think Steve is working on his post count. No there is only one regulator and I think yours is fine. I have it that the pressure went up in 96 with OBD II. http://www.jeep4.0performance.4mg.com/tech_specs.html
The "prime" suspect, (ha, ha), is the check valve in the fuel pump. Might be it should not let the pressure drop more than 20 Lbs in 1/2 an hour. Also an injector could leak as well as the regulator, but the check valve is what get's talked about. So...cycleing the key, it never goes over 10?
The "prime" suspect, (ha, ha), is the check valve in the fuel pump. Might be it should not let the pressure drop more than 20 Lbs in 1/2 an hour. Also an injector could leak as well as the regulator, but the check valve is what get's talked about. So...cycleing the key, it never goes over 10?
03-15-2012, 11:27 PM
#15
CF Veteran
Join Date: Aug 2011
Location: Nor-Cal Coast
Posts: 10,489
Likes: 0
Received 17 Likes
on
17 Posts
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Then don't post it! Post what you are pretty darn sure of, and if you are not sure, make it clear! 
On the injectors leaking....after cycling it, try just turning the key to start it, (no throttle), and see if it misses for a second compared to not cycling it.
The leaking might flood a cyl (or more) and make it miss.
On the injectors leaking....after cycling it, try just turning the key to start it, (no throttle), and see if it misses for a second compared to not cycling it.
The leaking might flood a cyl (or more) and make it miss.