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4.0 engine problems


theGreatDane

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my 1999 ranger has the 4.0 liter v6 and 4 wheel drive. my truck has presented the cylinder 6 misfire code twice in the last 6 months, which I have fixed with a new spark plug in that cylinder. The other day, however, it started stuttering heavily under load, and all of the sudden had very little power, and started getting very bad fuel economy. The check engine light came on soon thereafter, and when I pulled the codes, it gave me a P1151 and P1152 that said pending, and then i erased the codes. yesterday, i got another check engine light, and this time it was a p1151 and a cylinder 5 misfire code, and was accompanied by a very rough idle, and occasional bogging.

I just replaced the 2 upstream O2 sensors a couple months ago, and then the downstream one yesterday, thinking that might be the problem, along with cleaning the MAF. Didnt help.

I need this fixed soon, as it is my daily driver. What should I do?:icon_confused:
 


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CurtisP87

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Maybe your fuel delivery is too rich, causing the spark plugs to foul up...this reminds me of a problem I had once with my old car, a nissan 300z...
If one cylinder misfired, the ecu would recognize it, then pump more fuel/air into the other five cylinders to try and compensate for the lost power/timing of the one weak one. If driven like that for a while, the extra richness would cause problems with the other five cylinders (fouling of spark plugs, fuel injectors) which would just compound the problem...
I'm not sure if our ford engines work the same way or not, but I thought id throw it out there.
Good luck
 

RonD

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The '99 has a returnless fuel system so fuel pressure should be about 60-65psi with engine running, and hold that pressure when revved up and when key is off.
There is a check valve in the fuel tank with the pump that holds the 60psi pressure.
Because of the way the system works the fuel pump is not running all the time, the computer turns it on based on engine RPM and vehicle speed, it has no reference to actual pressure.
So if this check valve is leaking(or you have a leak in the fuel system), then the fuel pressure could be dropping while you are driving, say down to 30psi.
As pressure goes down O2 sensors detect leaner mix so computer opens injectors longer to richen it up, then fuel pump comes on and you are back at 60psi and injectors are opening too long and instant rich mix is the result, so O2 reports that as well.
I would check the fuel pressure just to be sure.

Or it could just be a vacuum leak :)
Also make sure the air plenum(big air tube between air filter and intake) is free from an cracks that could let unmetered air in, the MAF only works if all the air going into the engine passes thru it.
 
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theGreatDane

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Okay, how would i check the fuel pressure, and how would i check for vacuum leaks? i have also heard that my injectors might be bad/dirty.
 

RonD

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On the fuel rail there is a schrader valve(looks like a tire air valve) you need to connect a pressure gauge to that to read pressure.
You can often rent these tester.

Some use starting fluid on a cold engine, while engine is idling spray it around vacuum line and listen for engine to rev up or ping, if it does then where you just sprayed has a leak.
Cold engine because hot exhaust can ignite stuff like that.
 

theGreatDane

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alright, i will check that out tomorrow. i have noticed in my driving it today that if it starts stuttering, i can floor it, and it hesitates for a second, then seems like it clears itself and gets a surge of power.
 

adsm08

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Don't use starting fluid for the vac leak test. Use brake cleaner, wearever brand if you can get it (sold at Advance Auto). It is flammable enough to give you results, but it won't flash ignite on hot exhaust (which doesn't take long to get hot). Also, it will clean up your engine as you look for a leak.
 


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