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Hacks off Parts while Lit
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Discussion Starter · #1 ·
im battling what i beleive to be a vacuum leak on my 90 4 banger. After i start it up, about 10-15 secondds later, the idle speed increases to around 1500 RPMs and sometimes even 2000. Also, in the 2000-2500 RPM range at part throttle i get a serious miss/bucking sensation. Depressing the gas farther or less cures the bucking. In order to get my idle where it belongs, i had to fully remove the screw on the idle compensator deal. I've chased vacuum lines everywhaere and think theyre all normal, so im thinking it might be some soret of sensor that controls vacuum or something? anyone have any ideas??
 

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I had an 89 2.5 that did a simalir thing sounds like vacuum or faulty EGR valve my 89 did not have to many vac lines and worst case a head problem, crack or burnt valve which in my case was a burnt vavle, I removed it and reinstalled it and I think it ran around 100 bucks for the head work. Hopefuly someone else has cheaper options for you.
Any white smoke when reving up? Mine did.
 

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The EGR valve itself may be seperateable for checking-- its a clamshell deal--open it up, and there should be a rubber diaphram inside--on the 87s+ they usually rott out in 10 years or so-- cause`s bad idle, bad spot in the 1200 to 1500rpm range, stalling when flooring it...ect.

If in doubt, bypass and retest.

might want to check the map sensor as well--

have you hooked up a vac guage while the engine is running? and if so, how long do you hold vac after shutdown?
 

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Discussion Starter · #4 ·
i replaced the EGR valve but still have no joy. If i pop off the vac line to the MAP sensor, it idles well. For now, i have completely removed the screw adjuster in the idle compensator and it idles well. however, i still have a strong miss in the 2K RPM range, but ONLY if at part throttle (i.e. just holding speed). Everywhere else, it runs good. Also, if i let it miss much, then completly shut off the throttle, i occasionally get a back fire. i was thinking that might mean its getting rich and losing raw fuel...but i also thought that could be a timing issue BECAUSE of the vacuum loss. im not smoking at all, and, i havent checked the compression, but when i changed the plugs they all looked real good. so far, i replaced the EGR valve, O2 sensor, intake/exhaust manifold gasket, plugs, and reconnected a helluva lot of vacuum lines. the part throttle miss is still present though. i was considering RE-pulling the intake and adding some RTV, but im doubtful that itll do any good....

i dont have a vacuum gauge, but was considering getting one to help diagnose this.....

also, i have a slight-mild exhaust leak where the manifold meets the exhaust pipe. i doubt that matters...but just thought id throw that out there, just in case.

thanks for the help so far guys...
 

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""also, i have a slight-mild exhaust leak where the manifold meets the exhaust pipe. i doubt that matters...but just thought id throw that out there, just in case.""

incorrect to a degree-- an exhaust leak makes for less backpressure- it will cause problems at some time, but not really to the extent your talking about-- if the manifold gasket has any leaks in it, then there WOULD be your problem-it does exactly that. A leak at the "Y", which is common on ours, causes a mild to drastic loss of power (and melting of wires close by-clutchline) and a possible source of fire with the usual oil leaks.

If you pulled the map sensor vac line, and it idled good- not high, but the normal 700/1000 rpm, then the MAP is suspect and needs to be checked for correct output voltage-- likewise the TPS needs to be checked for a dead spot with an ohms meter. The older they get, the more likely the TPS will develop a dead spot-- ie: if you ride around for years at 1500rpm, your dead spot will probably be right around that rpm.

I`d do a complete inspect myself-
clean the TB, the IAC, and verify that the TPS is within tolerance with no drastic dead spots- check the map for correct output voltage-- double check for pressure leaks at the manifold wile running-- and get a cheapo vac/pressure guage, which also comes in handy for testing fuel pressure. Run a leakdown test to see how long it holds vacuum after shutdown, and a running test to see if its a steady vac signiture, or its jumping all around the dial. If it holds vac after shutdown for more than 20 seconds or so-there aint no leaks...if it has no vac right after shutdown...its time to start replaceing lines.

backup plan- verify the cat isnt plugged up-that the exhaust isnt kinked, and theres no potatos shoved up the tailpipe.
 

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Discussion Starter · #6 ·
Ed,
Thanks for all the advice. you're giving me some excellent points to check.

I have replaced the intake/exhaust gasket, so i dont think thats it (although i coulda botched the job i suppose).

For the MAP sensor, does anyone happen to have the voltage it should have or know a way i can check it?

same question for the TPS.

The throttle body was pretty nasty but i cleaned it when i did the gasket/plugs/etc.

I will pickup a vacuum gauge thursday and check that.

i took it out on the "proving grounds" toniight and had a couple interesting revelations:

1. When i stalled out, the 4wd light went out, making me think maybe it is losing vacuum fast (or maybe it just goes out?)

2. At one point, i punched the gas hard, and the 4wd light went out (doesnt vacuum drop as RPMs increase? would this also support the vac theory?

3. It is 100 times more fun wheeling a jeep than a fullsize. i found a couple of super fun technical trails that my truck could never have even dreamed of.

4. I have no catalytic converter. its been repiped (somewhat crappily) all the way back. there is a el-cheapo muffler, but no cat.


As always,thank y'all for all the help. the project IS coming along, just not as fast as i had planned on (isnt that always the case?) : )
 

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check my old, old website (not the old one, the old, old one) and look under "XJ/MJ info"-page down untill you see "catilitic scandal"--
http://groups.msn.com/RattsNest
its a storage site now...one of my first sites I no longer really maintain, but keep up as a "look what I did" kind of laugh.

look for a post on here from yesterday from me to "junkman" whos working his XJ for MAP test info-/CPS info...believe it was on here...I visit soooo many forums...the brain fog over. :confused:

Ive got the equation for the TPS test here somewhere...its a precentage of voltage thingy-I`ll try an dig it up today....but I think you`ll find the catilitic story may fit your reading pleasure.
 

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Discussion Starter · #8 ·
haha. iknow what u mean, hard to keep up what u posted where. unfortunetaly for me, i dont think u posted the MAP test info (i could be wrong, but i looked at ur post history or whatver).

thanks for the link to ur site, that sounds like my kind of luck with ur cat. hahaha.

i looked in my chiotons (or haynes, i cant remeber which i have for the jeep) but it was worthless in terms of testing the sensors. it pisses me off, they give u step by step instructions to rebuild ur engine but when it comes to pulling out the ol' impedence meter, it says, take it to a reputable repair shop. ugh. id like to get my hands on a FSM for cheap. anyway, if u could find any of that info, id appreciate it. i hate to keep pumping you for more info, but i do appreciate the help....
 

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whitebuffalo said:
haha. iknow what u mean, hard to keep up what u posted where. unfortunetaly for me, i dont think u posted the MAP test info (i could be wrong, but i looked at ur post history or whatver).

i looked in my chiotons (or haynes, i cant remeber which i have for the jeep) but it was worthless in terms of testing the sensors. it pisses me off, they give u step by step instructions to rebuild ur engine but when it comes to pulling out the ol' impedence meter, it says, take it to a reputable repair shop. ugh. id like to get my hands on a FSM for cheap. anyway, if u could find any of that info, id appreciate it. i hate to keep pumping you for more info, but i do appreciate the help....
incorrect- the more info that gets posted, the less people have ask for it...as long as they can look..that seems to be a universal problem in todays world...
Its not the peope who cant look-its the people who can...and just refuse to.
I answered a question yesterday on another forum that required me to type one word into google-the answer was on the first line....when I asked if he had searched, he asked "why? all i need to do is ask-one of you guys will answer "....argh. :mad:

anyways...you probably have the haynes manual-their favorite quote is "beyond the scope of the home mechanic-take to authorized service provider"...go buy a chiltons, and use the haynes for firestarter.
Ive got an online version of a FSM for the electronics-mostly underhood stuff-- email me and I`ll send you a copy--
PDF file- believe its 1.4meg.
87-90 underhood/fuel injection.

MAP test:
Key on-
unplug connector-
test for voltage between C and A- harness side-
voltage should be = 4.5 to 5 volts
reconnect connector-- backprobe terminal B
terminal B should be 4.5 to 5 volts
START ENGINE_>
backproble terminal B again-- voltage should now be 0.5 to 1.5volts.
 

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Discussion Starter · #10 ·
beyond the scope of the home mechanic-take to authorized service provider"

LMAO.....yup, thatd be the term. what a scam. email sent, and i will do that MAP test asap. thanks for the info
 

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whitebuffalo said:
beyond the scope of the home mechanic-take to authorized service provider"

LMAO.....yup, thatd be the term. what a scam. email sent, and i will do that MAP test asap. thanks for the info
its actually *good* to have both haynes and chiltons on hand...one`s good reading, the other is a comic. But they both have some info usefull..I just havent found any in haynes yet...I`d check, but its beyond the scope of the home reader... :D

I guess its better than nothing....at least the covers purty, and it holds down stuff.
 

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Another thing to look at is Fuel Psi or Volume. As Vacuum drops, the map sensor interprets that as high engine load, and tells the computer to add fuel. If you pulled the vac hose off the map and it ran better, I would suggest you check the fuel pressure. Also, when was the last time you changed the fuel filter?
 

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Ed in North Ga. said:
incorrect- the more info that gets posted, the less people have ask for it...as long as they can look..that seems to be a universal problem in todays world...
Its not the peope who cant look-its the people who can...and just refuse to.
I answered a question yesterday on another forum that required me to type one word into google-the answer was on the first line....when I asked if he had searched, he asked "why? all i need to do is ask-one of you guys will answer "....argh. :mad:
I have to say I disagree with you to a point. One thing I really like about this forum is that it hasn't had the "look it up before you ask" mentality. I'm always happy to help someone if I may possibly know something they don't. The purpose of a discussion forum is just that, to discuss. In this case, Jeeps. Besides all that, someone asking a question that has been asked before may just help someone else get on the right track if they have a similar problem, but don't know where to start. :)
 

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I like how you say "to a point".
I myself will go out of my way to help someone- ask around, my name is the same on many forums.

What gets me is the person who buys a jeep, and dosent bother to open the owners manual to find an answer that they already have-- someone who would rather have the answer handed to them, than to put forth any real effort to find out for themselves.

Some of the other forums I visit are starting to show signs of these types of "people"....one forum I visit has 10 posts with the header " leaking oil/oil pumps/rear main seal" in some such way. Each post has between 5 and +30 replies on how to do a rear main seal, why you should do an oil pump at the same time, how to do the oil filter o-rings...ect"....without fail, I opened it up today-theres a new post on top, above the old ones."HELP_ASAP!!! how do I do a rear main seal???"-"my rear main seal thingie is leaking all over my exhaust pipe- I need to do a rear main seal- what do I need to do, and should I do an oil pump at the same time??? help!!??"
The head/lead posts following it were listed in view-- each of the 10 posts already had the exact information he needed, showing up on that page- when asked if he had read any of these posts, his reply was simple- "I didnt bother to look". He wanted the info- he needed it ASAP- but didnt put forth ANY effort to find what he needed...and it wasent two clicks away. Is THIS person worthy of telling the information? retypeing whats already there so he can have it "personalized"? Does he think he`s special? no- he`s lazy. After being told where to find the information, he became bitchy and foul mouthed because we (appearently everyone within that forum) didnt want to answer his question-and he left. Information provided, got bitched at, an wasent even thanked. :p

Now- had he requested further information- the finer points of a rear main seal swapout- the torque settings on the bolts holding the oil pan- the correct diameter of the o-rings to use that really do work and dont cost a fortune....then yes, it would be a post worthy of open discussion to a person who needed the know how....what he had asked had been answered already....multiple times...on the page -within plain view.

following that- had the answers been archived, or paged to the next page, someone could have easily given him the URL-- had it been further hidden, it would have been a simple task of telling him exactly what he needed quickly and get him back safely on the road without driveing a firebomb.

What galled me, and probably every other person who opened that post, was his simple reply- "I didnt bother to look"-- this may strike you as me sounding like I`m all important and have little time to spare on people who are lazy-- its not quite like that-- I have very low tolerance for lazy people, I help every single person I can with information that will help in my time online, and I`m short on computer time- Ive got a window of about 2 hours where I can help who I can every day- inbetween research on things I need to learn to help me understand stuff so I can answer questions that I havent got a clue of answering. I am an information junkie who likes to help. Its all my fault. :D

so- I`m happy you disagree with me "to a point"- because deep down, I think you know exactly where I stand. And we can agree to disagree, and everyones still happy-even if we all agreed.
 

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Well, all I can say is is that it is a discussion forum. We don't have to answer anyone we don't want to. If we don't like a topic because we have seen it before we can dodge it. I remember years ago I had a teacher that when you asked a question, would reply look it up. That's not a teacher. I guess I'll do my best to be a teacher.
 

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Oh yeah. I was just trying to be polite when I said I disagreed to a point. We can still be friends though. :)
 

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amerijeep said:
Well, all I can say is is that it is a discussion forum. We don't have to answer anyone we don't want to. If we don't like a topic because we have seen it before we can dodge it. I remember years ago I had a teacher that when you asked a question, would reply look it up. That's not a teacher. I guess I'll do my best to be a teacher.

true- you(I /we/us/them) dont have to answer anything, and you can avoid posts..., but that IS why we come here. Someone needs the info we have (or dont)- but more times than not, even if its been posted before-we can lead "the horse to water"...weather the horse learns or not is his/her/its fault. You cant push his head down into that water and make him drink-he`ll just get pissed and go somewhere else. :D
For me, its a part learning experience, part shareing info-- if I dont know it, I read it, digest it, verify it, then I know it....I pass it on. Honestly, i think thats what "forums" evolved into in the last 5 years. The original forums, or BBS`s were nothing more than story boards...people would tell a story-and somewhere in that story would mention a question they had...within the answers to the post, someone would give advice-maybe even answer the question....all super informal, but man, it would take you an hour to read through everything.

somewhere down that road, they began question an answer boards, followed by open forums...kinda what we have today.

quicker, easier, faster-- more consise (unlike my typeing which is random and cant seem to stay on topic for the life of me :p )

anyway- point taken. been there done that. lets keep the forum good. :D
 

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Thanks, Ed. I enjoy a little debate every now and then. Now back to our regularly scheduled program.
 

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khenderson said:
glad you guys go that all settled!! :D i'd hate to have to put you two in time-outs!!!

I wish someone would put me in time-out. I need the break.

We were only debating, that is all. I have high regard for Ed's intelligent, and well spoken opinion. I wish I were the master-debator he is. :p (joke)

Now then, can you guys believe I haven't driven my Jeep in like three weeks? I have been so busy with work, I haven't had time. It's making me irritable :mad:
 
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