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So When my son got home, I tested it again, hot. pressure definitely did not hold. So, pressure with engine hot and everything off was 20. Hot with prime, went to 40 then immediately leaked down. Hot and running, pressure held steady at 47, then when switched off dropped quickly to 15. Can hear fluids "draining" as soon as I shut the car off... Not sure if that's related. Appreciate your help!Originally Posted by bluejeep2001
Im trying to think of an easy way to check for a leaking injector yourself without sending them to a shop...First...try the same test on a fully warmed engine...if the pressure holds it might be an injector issue...I don't see a check valve warming up and getting better. but an injector ..easily could. You should be able to pull the rail and injectors out of the head without disconnecting the fuel feed line...If you then PRIME only you could see if any of the injectors leak thru....DO THIS ON a COLD engine ONLY.AND MAKE SURE THE INJECTOR LOCK COLLARS ARE INTACT.. Have you pulled the plugs if one or more are leaking that/those plugs might seem wetter or sootier than the others....Do you have an air compressor...take each injector out completely and slide some rubber tubing over the inlet side hook the other end to your compressor and crank the pressure to 40-50 psi...see if any of the injectors pass air...The check valve is only there to trap pressure for the start before there is a constant run signal to the pump once the pump is running the check valve is wide open and serves no purpose so it would not cause a rough running engine when cold...depending on your mechanical abilities you could disconnect the fuel line from the rail and hook up a gauge directly to the feed line...if it holds pressure after prime then check valve ok...I think a whole new set of stock injectors is cheaper than dropping the tank to change out the check valve so you have a 50/50 shot even if you do nothing...but you should be able to isolate with just a minimal amount of work...AND its not winter
Old fart with a wrench
Fuel injectors don't pass any fuel until they get a signal to open, then they open fully. The computer cycles the internal valve's open time to control mixture, shorter time for a lean mixture and longer time for a rich mixture. It determines "on" time by reading TPS and MAP signals, air and engine temperature, and vehicle speed as well as 02 sensor readings after the cylinders have fired. All this in microseconds. Not only that, but each injector delivers fuel in sequential firing order only to the cylinder that will fire next as the valve opens, determined by the CkPS and cam sensor.
Early mechanical injection systems, like Rochester's system for Corvette, sprayed fuel into the port constantly so a large portion of liquid fuel was waiting in the port for the valve to open. Not efficient at all! The amount of fuel sprayed was controlled by throttle opening and vacuum levels.
NJXJer, the fluid you hear draining is probably the engine oil from the head.
Early mechanical injection systems, like Rochester's system for Corvette, sprayed fuel into the port constantly so a large portion of liquid fuel was waiting in the port for the valve to open. Not efficient at all! The amount of fuel sprayed was controlled by throttle opening and vacuum levels.
NJXJer, the fluid you hear draining is probably the engine oil from the head.
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Originally Posted by bluejeep2001
Im trying to think of an easy way to check for a leaking injector yourself without sending them to a shop...First...try the same test on a fully warmed engine...if the pressure holds it might be an injector issue...I don't see a check valve warming up and getting better. but an injector ..easily could. You should be able to pull the rail and injectors out of the head without disconnecting the fuel feed line...If you then PRIME only you could see if any of the injectors leak thru....DO THIS ON a COLD engine ONLY.AND MAKE SURE THE INJECTOR LOCK COLLARS ARE INTACT.. Have you pulled the plugs if one or more are leaking that/those plugs might seem wetter or sootier than the others....Do you have an air compressor...take each injector out completely and slide some rubber tubing over the inlet side hook the other end to your compressor and crank the pressure to 40-50 psi...see if any of the injectors pass air...The check valve is only there to trap pressure for the start before there is a constant run signal to the pump once the pump is running the check valve is wide open and serves no purpose so it would not cause a rough running engine when cold...depending on your mechanical abilities you could disconnect the fuel line from the rail and hook up a gauge directly to the feed line...if it holds pressure after prime then check valve ok...I think a whole new set of stock injectors is cheaper than dropping the tank to change out the check valve so you have a 50/50 shot even if you do nothing...but you should be able to isolate with just a minimal amount of work...AND its not winter
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Early mechanical injection systems, like Rochester's system for Corvette, sprayed fuel into the port constantly so a large portion of liquid fuel was waiting in the port for the valve to open. Not efficient at all! The amount of fuel sprayed was controlled by throttle opening and vacuum levels.
NJXJer, the fluid you hear draining is probably the engine oil from the head.
Gotcha. So draining sound is not related. So based on the fact it still leaked down when hot, plus the fact that I changed the plugs last weekend and all had the same powdery white look at the ignition side of the plug is pointing to a bad check valve/get a new fuel pump, correct?Originally Posted by dave1123
Fuel injectors don't pass any fuel until they get a signal to open, then they open fully. The computer cycles the internal valve's open time to control mixture, shorter time for a lean mixture and longer time for a rich mixture. It determines "on" time by reading TPS and MAP signals, air and engine temperature, and vehicle speed as well as 02 sensor readings after the cylinders have fired. All this in microseconds. Not only that, but each injector delivers fuel in sequential firing order only to the cylinder that will fire next as the valve opens, determined by the CkPS and cam sensor.Early mechanical injection systems, like Rochester's system for Corvette, sprayed fuel into the port constantly so a large portion of liquid fuel was waiting in the port for the valve to open. Not efficient at all! The amount of fuel sprayed was controlled by throttle opening and vacuum levels.
NJXJer, the fluid you hear draining is probably the engine oil from the head.
Old fart with a wrench
I would get another set of injectors before I dropped the tank.
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I thought if the pressure still dropped when the injectors were hot it pointed towards check valves as the issue. Just trying to understand... Appreciate it!Originally Posted by dave1123
I would get another set of injectors before I dropped the tank.
Old fart with a wrench
It could be either...or both! It's easiest and most cost effective to change the injectors first. Then you'll have new efficient injectors and can eliminate that as the problem. If the ones you have are washing down the cylinder walls with fuel, that's not good. Dropping the tank can be a nightmare, especially if you snap the bands holding it in. People have cut holes in the floor to avoid hassling with dropping the tank.
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Ok, well that makes sense. Would ya go 4 or 12 hole? Any recommendations for who/where to buy?Originally Posted by dave1123
It could be either...or both! It's easiest and most cost effective to change the injectors first. Then you'll have new efficient injectors and can eliminate that as the problem. If the ones you have are washing down the cylinder walls with fuel, that's not good. Dropping the tank can be a nightmare, especially if you snap the bands holding it in. People have cut holes in the floor to avoid hassling with dropping the tank.
Old fart with a wrench
My personal preference is 4-hole, only since that's what I put in my WJ and have had good luck with them. I also think they would be less likely to get fouled by contaminated fuel. The original Siemens are squirt guns in comparison.
precisionautoinjectors.com reconditioned Bosch 4-hole injectors for Jeep 4.0L engines
precisionautoinjectors.com reconditioned Bosch 4-hole injectors for Jeep 4.0L engines
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precisionautoinjectors.com reconditioned Bosch 4-hole injectors for Jeep 4.0L engines
Brother, you've been a big help. If you're ever in NJ, the beer will flow freely for ya. Thanks!Originally Posted by dave1123
My personal preference is 4-hole, only since that's what I put in my WJ and have had good luck with them. I also think they would be less likely to get fouled by contaminated fuel. The original Siemens are squirt guns in comparison.precisionautoinjectors.com reconditioned Bosch 4-hole injectors for Jeep 4.0L engines
Old fart with a wrench
Check out "D&E in the garage" on Youtube. Those guys are great and live in northern NJ, I believe. I was BORN in NJ in 1945. Bloomfield. My stepfather was a naval officer so we moved out when I was 5. My wife was born in Brooklyn, so I've been back in the area many times, although not a many moons. There is NO WAY to get me to live there or NYC.
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Yeah it's definitely a pricey and now a bit more dangerous place to live. I'm happy to live in a very rural part of NJ.Originally Posted by dave1123
Check out "D&E in the garage" on Youtube. Those guys are great and live in northern NJ, I believe. I was BORN in NJ in 1945. Bloomfield. My stepfather was a naval officer so we moved out when I was 5. My wife was born in Brooklyn, so I've been back in the area many times, although not a many moons. There is NO WAY to get me to live there or NYC.
So I took another piece of your advice, disconnected the fuel line from the rail figuring I do a pressure test from there but didn't have an adapter I could stick in the fuel hose that I could run back to the pressure guage. The guage I bought came with a bunch of adaptors, course none of em worked in this case... Any thoughts on what I could use?
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Oct 20, 2021
- Join DateOct 2018
- LocationHunt County Texas
- Posts:1,096
- Year1995
- ModelCherokee (XJ)
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get an extra set of hands. start the jeep crawl under neath and find the soft line going from the tank to the hardline. get a pair of clamps or vicegrips and when you get ready have the other person shut the Jeep off and immediately clamp the fuel line. If the pressure holds, your injectors aren't leaking and you've narrowed it down to the check valve or pressure regulator in the tank.