Max Compression?

[techsvcs]

Hello, i am new here and have a question. I ran a compression test on my Ranger 2.9 and the book says 101psi min, can anyone please tell me what is considered high compression i had 175 to 180 psi on all 6 cylinders also i have a lot of carbon build up on my plugs and am wondering if i need to decarbonize my heads? any help would be greatly appreciated some of my friends told me this was the place to find friendly willing to help people, thanks in advance!

 

[Twizzler09]

175-180 sounds right about on target if you ask me. The 2.9L is just the earlier version of the 4.0L in essence, and the 4.0L's run around 180psi from the factory.

If your compression was too high, you'd notice the spark knock (pre-detonation/pinging) pretty easily.

 

[srteach]

180 is great compression for an engine. That is at or close to new specs.

 

[techsvcs]

thanks guys, that's good then for an engine that's 22 years old. the reason i am going through all this is because my engine is surging esp when i first take off from a start it idles well though. i changed the plugs a year or so ago and then i changed them a week ago it was really running ruff before i changed the plugs all 6 were a covered in dry black sooty substance. a few months ago it would just quit running on me altogether i changed the ignition module and that fixed that. since then i have replaced the egr valve and cleaned out the manifold vac port cause it was completly stopped up i also changed out the air filter,fpr,02 sensor, inline filter about 4 months ago and canister filter and low preasure fuel pump and strainer. when i replaced the pump i noticed the hose connecting the pump to the sending unit was dry rot and the strainer had the black rubber stuck to it some of the rubber is still in the bottom of the tank as i took bed off to change instead of dropping the tank so i couldn't get all of it out. could that still be my problem or do you think it might be something else? Also 1 more question when i did my compression check when i turned over the moter the guage went to about 90 then 120 then 140 then 175-180 is that also normal? hey guys i really appreciate al of your help i jsut feel stuck!

 

[Big Jim M]

Surging

thanks guys, that's good then for an engine that's 22 years old. the reason i am going through all this is because my engine is surging esp when i first take off from a start it idles well though. i changed the plugs a year or so ago and then i changed them a week ago it was really running ruff before i changed the plugs all 6 were a covered in dry black sooty substance. a few months ago it would just quit running on me altogether i changed the ignition module and that fixed that. since then i have replaced the egr valve and cleaned out the manifold vac port cause it was completly stopped up i also changed out the air filter,fpr,02 sensor, inline filter about 4 months ago and canister filter and low preasure fuel pump and strainer. when i replaced the pump i noticed the hose connecting the pump to the sending unit was dry rot and the strainer had the black rubber stuck to it some of the rubber is still in the bottom of the tank as i took bed off to change instead of dropping the tank so i couldn't get all of it out. could that still be my problem or do you think it might be something else? Also 1 more question when i did my compression check when i turned over the moter the guage went to about 90 then 120 then 140 then 175-180 is that also normal? hey guys i really appreciate al of your help i jsut feel stuck!

First off the compression test does exactly what you describe in all engines. 175/180 is what we expect to get on a good running engine.
You don't describe the "surging" well enough to trouble shoot your problem.
1. Does it surge while idling?
2. Does it surge at part throttle?
3. Does it surge at wide open throttle?
4. Does it surge at steady hiway speeds?
5. Does it surge when going up a hill at full throttle?
5. While surging does it backfire?
6. Does this surge happen only cold..or hot?

Help us out here we need as much information as you can give.
Big JIm

 

[techsvcs]

hey thanks for answering jim! ok here goes answering your questions in order. 1) it idles pretty well at about 900 rpm it doesn"t really surge then but some times it will idle below 900 then back up to 900 but most of the time it idles pretty good. 2) when i give it slow throttle it doesn't do it as bad. 3)When i really get onit sometimes it will doit and sometimes it will be smooth. 4) at hwy speeds it doesn't do it hat much some times it will jerk sometimes it won't but it kind of rumbles out of the exhaust kind of like quiet steady backfires.5) not really 6) mostly it just jerks 7) out of all the things i have done to try and fix problem changing 02 sensor and plugs witch was the last things i did at the same time by the way that seemed to make it alot better so now most of the time it jerks is when it i first start the truck and first couple of blocks it surges preety bad but seems to get better the more the truck warms up. in the morn about 10 am is when i first start the truck but when i leave work abou 11 30 pm at night is when it runs it's best and sometimes then it doesn't jerk hardly at all. before i changed the plugs and 02 it was really bad more than just the jerking it would also loose alot of power sometimes even tried to die out and would really backfire type sound and on the hwy i would be giving it throttle and th mph would just keep dropping i would give it gas and still it would slow down i would lightly give it gas just to ty and maintain a good speed. i hope this helps if i am not answering correctly or you need more info please let me know. thanks jim.

 

[Big Jim M]

Guessing

hey thanks for answering jim! ok here goes answering your questions in order. 1) it idles pretty well at about 900 rpm it doesn"t really surge then but some times it will idle below 900 then back up to 900 but most of the time it idles pretty good. 2) when i give it slow throttle it doesn't do it as bad. 3)When i really get onit sometimes it will doit and sometimes it will be smooth. 4) at hwy speeds it doesn't do it hat much some times it will jerk sometimes it won't but it kind of rumbles out of the exhaust kind of like quiet steady backfires.5) not really 6) mostly it just jerks 7) out of all the things i have done to try and fix problem changing 02 sensor and plugs witch was the last things i did at the same time by the way that seemed to make it alot better so now most of the time it jerks is when it i first start the truck and first couple of blocks it surges preety bad but seems to get better the more the truck warms up. in the morn about 10 am is when i first start the truck but when i leave work abou 11 30 pm at night is when it runs it's best and sometimes then it doesn't jerk hardly at all. before i changed the plugs and 02 it was really bad more than just the jerking it would also loose alot of power sometimes even tried to die out and would really backfire type sound and on the hwy i would be giving it throttle and th mph would just keep dropping i would give it gas and still it would slow down i would lightly give it gas just to ty and maintain a good speed. i hope this helps if i am not answering correctly or you need more info please let me know. thanks jim.

So I'm guessing that your "surge" is everyone else's hesitation. I'm thinking it hesitates at certain times.
When you put new plugs in there did you use motorcraft or some other silly brand?
Did you install new wires? New cap & rotor?
Big JIm

 

[techsvcs]

yea i guess hesitation would be it jerk or surge is the only words i could think of at the time. i used autolite plugs and set @.44. i changed wires,rotor button and dist cap about a year ago so i didn't do them this time. my hesitation after driving today is mostly under acceleration from a dead start or if say i am driving 60 on hwy then speed up 2 say 65. just not as bad when i am already up and going.

 

[Big Jim M]

You could have any number of problems. Since it is 23 /24 years old I'd first start looking for vacuum leaks. One little hose losing vac can cause a problem such as yours. A manifold leak is quite possible also. Then you get into the lectric components. Might be the throtle position senser.. If it has any codes they might help in looking for the problem.
You might start another thread with your problem in the header.. Under this header few are reading your posts. You may find someone that has had your exact problem with your exact vehicle.
Big JIm

 

[techsvcs]

ok jim i will start another thread then i appreciate the help. when you say manifold leak are we talking intake or exhaust or it could be either one also how would i look for the manifold leaks? again thanks and i will start another!

 

[Big Jim M]

intake

ok jim i will start another thread then i appreciate the help. when you say manifold leak are we talking intake or exhaust or it could be either one also how would i look for the manifold leaks? again thanks and i will start another!

Intake, not exhaust. I use a small propane tank with a hose on it. I start the engine and while idling I turn the propane on and using the hose I spray propane all around the gaskets and hoses where there could be a leak. When the vacuum sucks in the propane instead of air the engine surges from the increased fuel..
If itis idling good the chances are it does NOT have a vacuum leak. Most likely it is the tps or some other lectric senser.
Big JIm

 

[AllanD]

Hello, i am new here and have a question. I ran a compression test on my Ranger 2.9 and the book says 101psi min, can anyone please tell me what is considered high compression i had 175 to 180 psi on all 6 cylinders also i have a lot of carbon build up on my plugs and am wondering if i need to decarbonize my heads? any help would be greatly appreciated some of my friends told me this was the place to find friendly willing to help people, thanks in advance!

Unless some were very low what you are supposed to look at is are they more or less the same cylinder to cylinder.

AD

 

[techsvcs]

they were not the same cylinder to cylinder but the were within 5%.

 

[kimcrwbr1]

I would say run a vacuum guage from the carbon on the plugs you probably looking at valve guide seals. In the tech library is a section on how to read a vacuum guage do you get black smoke out the exhaust when you start it after about 5 minutes of sitting when the engine is hot. To clean the carbon out of the cylinders you can try seafoam suck 1/2 a can in the brake booster when the engine is warm and shut it down immediately. Wait ten minutes and pour the other half in the tank and start it and rev it up and enjoy the smoke show also put a new pcv valve on it when you change the plugs cap and rotor. I recommend cap and rotor with plugs, and wires every third tuneup alot of volts going thru those wires note the plug gap. If you have a pcv it could be your intermittent dead spot. A good vacuum guage never lies.