Pulling my hair out - JeepForum.com
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post #1 of 28 Old 07-25-2020, 05:33 PM Thread Starter
jeepster96zj
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Pulling my hair out

98 4.0L - Ive searched and searched the forums so forgive me if this is answered previously. The other day I was idling in a parking lot and the radiator cap exploded and coolant shot out everywhere. I replaced the radiator cap but then the car started doing something weird. At idle everything runs perfectly but when put into gear it bogs down and idles rough. It'll run but typically when braking it stumble and die. There was a brief p0108 code that popped up but after changing the MAP sensor it still has the same problem. The weird thing is I can run the car with the pcv intake tube unplugged from the intake manifold AND the brake booster vacuum line unplugged. I shouldn't be able to run the car with that much vacuum leak I'd think. The idle just goes up but the car will run. I've tested the wiring to the map and its in spec, Ive check the wiring at the PCM and its in check, i cleared the grounds by the battery and the one on the passenger side of the motor (couldn't find any elsewhere), I've replaced the IAC, the TPS, the spark plugs, and both PCVs. Still stumbles and dies. I checked the fuel pressure, 45psi while idling and holds pressure while driving and even when it stumbles and dies. I cut a couple of small holes into the cat to see if air was getting through and plenty of air is coming through the cat. I an getting blow-by out of the oil cap and the intake vacuum fittings. Im also reading 15hg in MAP pressure at idle which seems really high. I simply cannot figure out what is going on. Its almost as if there is not enough air coming in to the intake or there is a vacuum leak I cant find. Any help or insight would be supremely appreciated.

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post #2 of 28 Old 07-27-2020, 02:20 AM
riiz
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Have you back-probed the MAP with a voltmeter while the engine is running and verified that the new sensor is functioning correctly, outputting around 1.4v at idle? If a MAP is bad, most computers will richen the mixture as a default which would explain the ability to run with a massive vacuum leak.
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post #3 of 28 Old 07-27-2020, 02:49 AM
Tarneg
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i have 2 things i see stand out
1 the long term fuel trim is damn near maxing itself out to lean the vehicle (max most systems can do is 30% both ways) so thats interesting . the short time looks fine
2 when you say blow by from the oil cap and intake vacuum fittings do you mean like actual pressure. in that your crank case has pressure build up in it ? cause if so either some line is pumping air into it or you need to do a compression and leak down test to see if the cylinder walls and rings are good

and the map sensor sucks to try and read so ya have to find out if it omits the standard atmosphere in that reading or if its the true number, kind of a pain

best i can help wwith atm so good luck
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post #4 of 28 Old 07-27-2020, 06:57 AM
At1bob
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Do a compression Test. Stuck Rings or valves...... after thinking about this a little is there a chance you blew the head gasket and you are pushing exhaust into you radiator?

Last edited by At1bob; 07-27-2020 at 11:39 AM.
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post #5 of 28 Old 07-27-2020, 06:57 PM Thread Starter
jeepster96zj
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Thanks guys! I back probed the MAP and it idles around 2.4v and goes down to 1.2ish when the throttle opens. Not sure if thats too far out of spec.


I think blow by may just be oil burning so my next test will be a compression check. I'll let yall know what readings I get.
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post #6 of 28 Old 07-28-2020, 04:04 PM Thread Starter
jeepster96zj
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Quote:
Originally Posted by At1bob View Post
Do a compression Test. Stuck Rings or valves...... after thinking about this a little is there a chance you blew the head gasket and you are pushing exhaust into you radiator?

Compression check came back good. Every cylinder was at or above 130psi.
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post #7 of 28 Old 07-28-2020, 04:54 PM
jtec
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post ALL the codes .

The ECT us low. hw long did eng run?
What is B1S1 o2 sensor Voltage readings?

As mentioned the fuel trims are AFU - pull the plugs look for a fouled plug, maybe a leaking injector.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 28 Old 07-29-2020, 03:35 PM Thread Starter
jeepster96zj
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post ALL the codes .

The ECT us low. hw long did eng run?
What is B1S1 o2 sensor Voltage readings?

As mentioned the fuel trims are AFU - pull the plugs look for a fouled plug, maybe a leaking injector.

That was the only code. I cleared it and I've driven it around the neighborhood and it hasn't come back.


Engine will run as long as I leave it on if its in neutral or park. Once I put it in gear it will bog down and if I drive it around and come to a stop it will sputter and fight to live but eventually dies.


I'll have to check o2 voltage when I get done working. I pulled all the plugs yesterday for the compression check and they look way too worn for having changed them 5000 miles ago. I'm thinking its because the A/F mix is way off.
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post #9 of 28 Old 07-29-2020, 03:51 PM
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the ECT is low - I asked if the engine was warmed up?

let us know about the B1S1 voltages.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 28 Old 07-29-2020, 08:05 PM
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Quote:
Originally Posted by jeepster96zj View Post
Engine will run as long as I leave it on if its in neutral or park. Once I put it in gear it will bog down and if I drive it around and come to a stop it will sputter and fight to live but eventually dies.
I know you have other issues, and I know it sounds stupid, but check your transmission fluid. Trans warmed up from driving, engine running, trans in Neutral.

Of course the big question is why did your radiator cap explode? Do you mean it actually broke loose and flew off?
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post #11 of 28 Old 07-29-2020, 08:44 PM
At1bob
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Quote:
Originally Posted by jeepster96zj View Post
Compression check came back good. Every cylinder was at or above 130psi.
What I don't understand is the blow by. I had an old Honda that had it so bad it was like a hair drier blowing out of the oil cap. The rings were shot on that car. It also seems that you have pressure in your intake manifold? Where is all that air coming from?

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post #12 of 28 Old 07-30-2020, 02:22 PM Thread Starter
jeepster96zj
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Originally Posted by jtec View Post
the ECT is low - I asked if the engine was warmed up?

let us know about the B1S1 voltages.

These are all the readings at idle at operating temp.
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post #13 of 28 Old 07-30-2020, 02:24 PM Thread Starter
jeepster96zj
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Originally Posted by RedRiverT View Post
I know you have other issues, and I know it sounds stupid, but check your transmission fluid. Trans warmed up from driving, engine running, trans in Neutral.

Of course the big question is why did your radiator cap explode? Do you mean it actually broke loose and flew off?



I was old and separated from the spring. The top was still on but it was basically a sprinkler head spraying coolant all over the engine bay. The pressure built up so high that the heater core cracked cause I had water all over the passenger side floorboard. I'll check trans fluid right now.
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post #14 of 28 Old 07-30-2020, 02:28 PM Thread Starter
jeepster96zj
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Just checked for stored codes and it has p1282 stored.
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post #15 of 28 Old 07-30-2020, 03:33 PM
rjbruzan
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When you did the compression check was one plug out at a time or all?

Of all the things Ive lost
The one I miss most is my mind

Its like a fart in a windstorm
It smells good but thats about it

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