hi..can u help me, my 96 xj wont run..stalls, goes, acts strange

[ezeman]

ok so I did another vac test, its now 8 in hg, so I think i definately got a vac prob. Now I keep the gage on, and pull and plug various vac tubes off the intake manifold with no change in vac pressure, does this mean intake gasket or something? Any other ideas on where to look? I thought I read something on the use of propane to trace this down..any ideas?

and low vac leads to the high MAP voltage, and likely my 3100 RPM rev limit, as the engine is likely straving as its too lean.

I can still limb/drive it around, but it stalls at stops (unless i give it some gas) and still chops out at 3000 RPM, right after the shift point!! woohoo

thanks again for your vac leak tracking help!

eze

 

[langer1]

ok so I did another vac test, its now 8 in hg, so I think i definately got a vac prob. Now I keep the gage on, and pull and plug various vac tubes off the intake manifold with no change in vac pressure, does this mean intake gasket or something? Any other ideas on where to look? I thought I read something on the use of propane to trace this down..any ideas?

and low vac leads to the high MAP voltage, and likely my 3100 RPM rev limit, as the engine is likely straving as its too lean.

I can still limb/drive it around, but it stalls at stops (unless i give it some gas) and still chops out at 3000 RPM, right after the shift point!! woohoo

thanks again for your vac leak tracking help!

eze

You need to cap all the lines off to find the one that leaking, don't forget your Vacuum brake booster

 

[ezeman]

hey thanks for the advice, I took each vac 'takeoff' line off and plugged it with my finger, one at a time. There was no change in vac pressure as I removed and plugged each one. So i am wondering if I still need to plug them all at once and take a reading? I though maybe the manifold was leaking cause i got no change by individually plugging each vac lead off the manifold..make sense?

thanks again

 

[Runnin'OnEmpty]

As Mr Langer1 says, don't forget the brake booster.

 

[MoFo]

The brake booster would be my most likely suspect too.

If you pull that hose and plug the fitting to the engine and still have the problem, I would suspect valves before a leaking manifold.

The propane test is dangerous and I don't recommend it. You have to take an unlit propane torch, turned on low, and hold the end very close to spots you suspect a leak. When it finds a leak, the propane is sucked into the intake and the engine RPMs will increase briefly, while the PCM closes the IAC valve. The engine will die when the torch is removed. This has to be done on a running engine and is a fire risk.

The best way to check for leaking valves is with a bleed-down test. You crank the engine untill the piston is at TDC and pump air into the cylinder, through a set of guages. Adjust your compressor so the first guage reads 100 PSI. There is a small orafice in the block between the guages. Air flows throght that orafice, past the second guage, then into the cylinder. If the second guage reads 88 PSI, you have a 12% leakdown. With a stuck or bent valve, I would expect an 80% or better leakdown (20 PSI on guage 2). I bought my bleed-down guage set at Summit for $75 about 5 years ago.

This check needs to be made on all the other cylinders too. You need to hand-crank the engine 1/3 of a turn, then move the test guages to the next cylinder in the fireing order.

 

[ezeman]

ok , I did the whole vac test, by plugging each one. I think its strange that it could be a valve or cylinder problem when the thing runs great between 1000 and 3000 RPM. I can also only drive it with the MAP disconnected, otherwise with the MAP connected it stalls alot and cuts in and out at random. The brake booster vac line has no effect on the vac guage when i disconnect and reconnect, i still get about 7 in Hg on the gage, ditto with connecting or disconnecting any other vac line off the manifold.

I also did a the 'spray liberally with brake cleaner" test as opposed ot the propane, and reall couldnt find any changes int he engine running when I sprayed nearly everything intake and vac related

So a bleeddown test is next on the list? Sounds involved but I hace already been so far, and got taken for 379$ at the mechanic already...gggrrrrr

thanks for sticking with me peeps

eze

 

[Runnin'OnEmpty]

Ezeman, there's one other thing that will cause low manifold vacuum and the other symptoms, and I don't know why I didn't think of it sooner:

CLOGGED CATALYTIC CONVERTER

If yours is like my 96, you can loosen the clamp that holds the cat on, and slide it back to open the exhaust up. Then test the manifold vacuum with the engine idleing. If the vacuum increases, then you need a new cat.....

Here's hoping that's it,
ROE

 

[ezeman]

ROE

Thanks for that suggestion. I changed the CAT about a year and half ago to a high flow cat, along wiht a new muffler. I will beat on the CAT to see if I hear anything chunky, but because the Jeep runs great other than this bad idle, limited RPM to 3000, and stalling stop signs, aka the bad idle, I think i can rule it out.

I am just stumped as to why last week i measured 11 in and this week its 8 in of Hg..

I am goin to retighten the manifold bolts again here this am, and think about the bleed down test or pulling the valve cover to see if i got bad valve, but again cause it runs so good otherwise....

thanks!

stumped .....eze

 

[langer1]

I am just stumped as to why last week i measured 11 in and this week its 8 in of Hg..

If the 8 was taken cold and the 11 with a warm engine that would explain it.

 

[MoFo]

EZE,

I wish I lived closer, I would bring you my bleed-down guages.

ROE had a good idea with the cat. Too bad it is so new, that kinda rules it out. How well do you trust the vacuum guage you have? Do you have a friend close with another you can check it against?

A vacuum leak is most evident at idle and should not affect high RPM operation. A valve problem, on the other hand, will be bad at idle and get worse at high RPM. You may not see a valve problem from the top. You would see a stuck valve, or a bent valve. You would see a collapsed lifter, but you would not see a burnt valve or a burnt seat.

A compression test guage is much cheaper than a bleed-down guage set. It is not as definative, but would pick up most valve problems.

Good luck and please let us know what you find.

 

[ezeman]

I guess I trust the guages as far as I can throw them, got them at Advance Auto for about 30-40$ bucks. I tightened the manifold bolts earlier today, none were real loose. I got a shitty, but not as shitty as usual idle after I cleaned the IAC and TB. I also reset the computer, and hooke dhte MAP back in to see what was going on again. I still got the low 7 in HG vac on the gage. The engine revved fine up to 5k RPM, but ran real bad cutting out at random again all through a low RPM range (1000-2500) while under load, and would go no faster under load. The exhaust seems plenty strong out the muffler to rule out the cat. Goin nuts here :S

I will try comp test perhaps tommorrow.

thanks again!!

eze