robbiebragan

Okay so here's the problem my car won't stay runnin if given any throttle....unless I unplug the tps and map vacuum and when I do that it runs decent but given more than quarter throttle it will bog down and almost die until I left off the gas...I've replaced the tps and map sensor and fue filter...it seems like its runnin rich cause when I floor it in nuetral it will go fine and blow black smoke at about four thousand rpms..... idk what to do any help would be appreciated I've heard that it could be the crankshaft position sensor or cracked exhaust manifold but I'm just lookin for answers before I fix things that aren't broken....and its a 91 cherokee 4.0 ho inline six thank you

EVcherokee

O2 sensor

XJeepWerks

x2 on the o2 sensor. Most of them are bad anyway, and replacing it with a good unit will increase your fuel economy. A bad o2 sensor can definitely cause you to run rich, or it can cause you to run extremely lean. My Jeeps o2 sensor is missing because my aftermarket downpipe doesn't have the mount for one and although it runs like a champ, my gas mileage greatly suffers because of it. Every engine will react differently to certain problems so don't base my Jeeps reaction to not having an o2 sensor against your Jeeps issue. An oldschool method to testing a crankshaft positioning sensor that I have heard of but never personally tried is to hit the motor with a hammer hard enough that it gives it a good knock, but not hard enough to break anything. Supposedly if the engine stutters when you hit it then the sensor is operating as it should (Not what it's designed for but that's supposedly a side effect it has.) I do not know if this test is true, but it certainly wont hurt to try it. If it stutters, then you know it's working. If it doesn't then I wouldn't sweat it, it could just be the test not working. I would also put a small piece of wood in between your motor and the hammer if you try it. Old rule of thumb with tools; never hit metal with metal, unless it was designed to do so. A hammer is designed to hit nails, not engine blocks. You could use a rubber mallet if you prefer, but I don't think a rubber mallet would deliver as much shock as a hammer and piece of wood. Black smoke generally says your getting a good hot spark, but your fuel is not atomizing correctly (As I understand it.) Common causes of fuel not atomizing correctly are getting too much fuel (bad o2 sensor) and injectors not spraying correctly (Bad injectors)


Just my .02 Hope it helps

XJeepWerks

Also, you should check your exhaust manifold for cracks. The ONLY thing good about having a cracked exhaust manifold is that it's not going to crack again. Even the slightest crack in an exhaust manifold can allow enough exhaust fumes to enter the cabin during long trips to cause you to temporarily lose consciousness which can have deadly results. That's about the worst case scenario with a cracked exhaust manifold and although not common, it has happened and will happen again. Cracked exhaust manifold can also cause problems with your engine running properly and cause you to fail inspection/emissions if your state requires it. I would recommend against buying an OEM exhaust manifold and/or cast iron manifold because it will most likely crack just like your current one in a short amount of time.

EVcherokee

Yeah a cracked manifold, up stream of the O2 sensor will trick the sensor into thinking your running lean, therefor making the motor run horribly rich. It will also make a hot spot down stream of the crack and fry a new O2 sensor, not to mention if its close enough to your valves you'll burn those up. Also the turbulance created in the exhaust stream will cause exssesive back pressure, hindering performance.

I had a crack in my manifold and I was able to weld it up rather easily. Its a common problem on these manifolds and lots of guys have welded theirs up with success, sometimes however, a crack will form on the edge of the weld, but another weld bead usually stops it there. I also welded my EGR bung shut while I had it off, which is legal to do if you don't have to pass emissions. Gained a couple pony's that way.

Carbon monoxide is a sneaky gas, odorless, colorless and causes symptoms easily misdiagnosed. You start by getting sleepy, slight headache and mild nausea, as exposure increases the symptons increase and can be confused with the flu, your vision will start getting blurred, you can't concetrate and you start shutting down from lack of oxygen. The only physical symptom is after moderate to heavy exposure and thats when you start taking on a "blush" appearance, usually in the face and tops of the arms. Shortly after that you fall asleep, lose consciousness and become comatose, your heart stops and you die.

kbad

hey man, x2 on vacuum leaks and temp and o2 sensors.....the temp sensor affects how the ecu adjusts the fuel/air mixture......got check engine light? any codes?.....look here for renix troubleshooting tips that may shed some light..... http://www.lunghd.com/On_Site_Tech.htm ....here for vacuum info.... http://www.jedi.com/obiwan/jeep/misc/vacuumhoses.html ....and here for egr info, you may need to purge the egr, which also affects fuel/air ratio at intake..... http://jeep.zerok.ru/index.php?page=90 ...good luck!

XJeepWerks

I responded to a call where a guy ran off the side of the road and fatally crashed. There were absolutely no signs of foul play or control loss from the scene. Turned out he passed out driving due to Carbon Monoxide poisoning and crashed. Nasty stuff that is highly under estimated. When I went through my Hazmat class, we had an entire chapter on just Carbon Monoxide itself.

robbiebragan

Okay so I have not replaced the o2 sensor yet but when I unplug it while the car is runnin it causes it to stutter and die...and the codes that it throws are tps and map but because I have those unplugged so it will even run somewhat that's probably what's causin it to show those codes....and also is there any trick to find out if my exhaust manifold is cracked without having to tear it all down? I did it once to replace intake gasket and it was a lot of work so if there's anyway I could do it without tearin it down would be awesome...but when I gas it it almost sounds like its suckin way to much air in and that's what's causin it to die down in power that's why unpluggin the tps makes it run better thanks a lot for your inputs ill check em when I have the time

kbad

...intake/exhaust manifold leak test.... http://www.lunghd.com/Tech_Articles/...iagnostics.htm

XJeepWerks

That test is only good for testing the seal made between the manifold and the block. The only ways I know to check an exhaust manifold for cracks is listening for an exhaust leak, and visual inspection.

notop46

I am thinking low fuel pressure. If it dies when you open the throttle, it is getting more air but possibly not enough fuel. The amount of fuel needed to spin an engine in neutral is alot less than it needs at speed.

If your O2 sensor is bad, it will mess up your fuel economy, but will not cause a problem like you are experiencing. The O2 sensor is only used to fine tune the fuel mixture. Fuel delivery is based primarily on air temp, manifold pressure, rpm, and engine displacement.

Exhaust leak is bad for your health, but will not cause your engine to run this bad.

Check your fuel pressure.

huntingman2706217

you can easily see the crack... normally where the 1,2,3, cylinder meet the 4,5,6 cylinders... easy to see... but i doubt its your o2 senson... i have yet to see where a bad o2 sensor causes a vehicle to run like crap... maybe run alittle rich... maybe run alittle lean... but never seen one cause a vehicle to choke out and die... its something else... could be alot of things... but doubt its a o2 sensor... vaccum leaks would be my number one guess if youve already replaced the sensors on the TB... start spraying starting fluid around the intake and head since youve been in there before... its it revs up ANY you got a vacuum leak there... do this all over the intake area...

robbiebragan

Okay so I don't think its the o2 considerin I have no cats on it its just straight pipe with a glasspack and I've tried sprayin carb cleaner and other things on the intake itsself to see if there's any leaks and the throttle stays the same. Is it possible for a valve cover gasket leak to cause this? I've checked all the vacuum lines and they seem fine

robbiebragan

And the fuel pressure seems fine just from pressin the valve down on the fuel rail with my finger...I tried a fuel pressure test but the tester I had didn't work for some reason

Bustedback

Sounds like the fuel pressure regulator may be causing the engine to flood by allowing too much fuel, the unplugged vacuum hose leans out the air/fuel mixture and the engine runs better. I've seen one on a Ford that had a ruptured diaphram and was sucking gas through the vacuum hose right into the intake manifold.