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no power at high rpm


swynx

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94 4.0

so started up the truck and noticed that it pretty much quits above 3k rpm, and i have a loud hiss when floored. it wont hardly do 65 iether. the hiss sounds like its coming from the passenger side.

its not missing, and it refuses to go above 4k, and its hard to even get it there. i pulled codes, i think it was 171, any who the book says its an 02 sensor running lean on bank 1, thats passenger side? i replaced both 02 sensors less that 2k miles ago. pulled them out they have barely discolored, tryed spraying them with maf cleaner, it did not help.

new

iac, maf, tps, fpr, fuel filter, fuel pump, spark plugs, coil, wires, both 02 sensors, engine coolant temp sensor, thermostat. i have new fuel injectors just need to put them in.

maybe it needs new gaskets on the top end, as its around 300k miles.

it only makes the hissing sound when past half throttle, i sprayed the engine down for like 5 minutes with the hose, while at idle, and while a buddy was gassing it making the hissing sounds. ive used propane to try and find a leak, but i have had no luck finding it.

also, i have a new cannister thing (agpete posted about it in another thread) but i havent installed it. i havent pulled the spark plugs iether, but its only been ran like this for a half tank. i was going to unplug the 02 sensors and see if any thing changes, and i also just read about the cat blowing the insides out, and having no power above 2k rpm with a whooshing sound. just looking for insight. thanks.
 
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RonD

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It does read like clogged exhaust.

Vacuum gauge can ID that, or.......

Drop the pipe after the "Y", loud but if RPMs go high and power is back clogged exhaust is the issue
 

swynx

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It does read like clogged exhaust.

Vacuum gauge can ID that, or.......

Drop the pipe after the "Y", loud but if RPMs go high and power is back clogged exhaust is the issue
ill check that tomorrow, i actually wouldnt doubt if it was clogged up, i have put the truck into clay pits and mud holes where it has been submerged past the oil pan.

also, the cat and exhaust runs on the passenger side...
 

kunar

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yep, im with ron, id be very suspect of the exhaust system being plugged.
 

swynx

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Tore the entire exhaust out. Made no difference.other than that it made my ears ring.

Drove it with iether 02 unplugged. Both unplugged. No difference. But I figured it wouldn't as it does this even when cold.

Spark plugs look new. Gapped at. .055

I bought a new fuel filter I'm going to put on later today.
 

FritzTKatt

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Proper gap is .054. Not too much difference, but it could help.
 

swynx

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fuel filter did nothing, i still hear the hissing sound, but i cant locate it.
 

RonD

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Smoke test

Cigar and glass of bourbon, some say bourbon is optional, they are not invited to my smoke tests :)

Remove intake's air plenum(big air tube) put saran wrap or ?? over the now open intake so it is sealed.
Remove PCV valve hose from intake and put on a longer hose that you can blow smoke into.
Light cigar, sip bourbon, blow smoke, repeat
Watch for whiffs of smoke
 

swynx

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So I haven't gotten around to the smoke test. But I was messing around and decided to check the upper and lower intake bolts. Every bolt I can reach was loose to the point I walked it out by finger. I think that could be a problem.
 

RonD

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Yes, 4.0l had tendency for loosening intake bolts
 

swynx

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update, replaced the upper and lower intake gaskets. the hissing sound is gone, and i scanned it for codes got nothing this time. however the truck still has no power.

could this be caused by a faulty crank shaft position sensor? could it have anything to do with the egr? the sensor is only 40$ so i thought about replacing it.

ive replaced nearly everything i can think of.
 

swynx

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So an update. I tore into the truck one last time before I sent it off. Was going to replace the fpr with one I had laying around and swap out the tps. I noticed I had a fuel injector unplugged. Plugged it in and it runs like a champ now.
 

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I'm glad you found it. I've done similar when my race truck wouldn't fire up after r+r the engine. After several months [NOT full time ] I finally found a wiring plug that I had taped wasn't fully engaged. Kicked my own ass a few weeks on that one.
 

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