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Discussion Starter #1
Help! extreme power loss [Update: consistantly LOW compression]

Update:

I did a compression check on the front 4 cylinders and found them to be between 75 and 85 PSI. I didn't do the back 4 because I ran out of daylight and they are too hard to get to. I know the guage is correct because I did a check on 1 cylinder of my 4.6 Cougar and it read a normal 180.
Is there is a possibility my timing chain could have slipped, therefore not opening and closing the valves at the right time. Hopefully, I'll have access to a timing gun this weekend.

Other than that what else might cause the compression to be consistantly this low across multiple cylinders?

Also, although my check engine light never came on, I did a code check and found 2 things:
1. EVP/EGR sensor voltage below closed limit
2. Thermactor air system inoperative (44)
To my knowledge these don't affect compression.


Original post:
I have an '88 351W with a C6, 33 inch tires.
The thing is a complete dog. On the highway it takes me about 30 seconds to get up to 60 mph (actual speed, not speedometer speed). At 60, the tach reads about 2300 floored and will not rev higher unless I go slightly downhill.....then it will do about 3000 rpm and 70 mph.
My friend says it is due to the 33 inch tires with a stock 3.55 rear. I disagree.

Here is what I have done to the truck since buying it:
- new spark plugs
- new plug wires
- replaced fuel filter
- replaced solinoid
- fixed bad ground
- replaced battery
- replaced exhaust manifold gaskets, upper intake gasket, valve cover gaskets
- had exhaust leaks fixed
- had 2 stage cats replaced with 1 cat

What could possibly be causing my extreme power loss?
The engine runs smooth and seems to run normal....it just doesn't have any power (and gets around 6 mpg in city).

Would testing the fuel injectors pressure per Chiltons be a good first step? I don't have much experience working on engines.
 

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how long did the truck sit before you got it? It could be bad gas try putting a higher octane in your tank for a little bit and also try alot of fuel injector cleaner
 

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Discussion Starter #3
The truck sat for at least 3 months before I bought it. I have filled the truck up with gas since I bought it - my friend filled up his Buick at the same time/place and hasn't had any problems.

....and I forgot to mention, the truck has never thrown any codes.
 
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How many miles on that engine? I would do a compression test and get codes! It would do better with lower gearing, but I agree, getting the motor right is first priority. Try Ryans site to get codes and learn your EFI. Most manuals, Haynes, are very helpful and may give a procedure for compression test. A basic comp tester is about $30 or barrow one. A comp test gives a general idea of the engines condition and if you having power loss due to low compression it can help diagnose ring or valve problems.

http://fordfuelinjection.com/index.htm
 

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pull the codes, test the fuel pressure, do a compression test basically what everyone else said.
 

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Ex Navy Nuke
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- Check the timing
- Check the dist cap and rotor
- Replace the O2 sensor and disconnect the battery for at least 15 min.
 

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Discussion Starter #8
This might seem like a stupid question, but how do you test the fuel pressure? My chiltons just has testing the injectors pressure.

Also, in the chiltons when it explains how to test the injectors pressure the 1st step states:
"Connect pressure gauge T80L-9974-A, or equivalent, to the fuel pressure test fitting. Disconnect the coil connector from the coil. Disconnect the electrical lead from one injector and pressurize the fuel system. Disable the fuel pump by disconnecting the inertia switch or the fuel pump relay and observe the pressure gauge reading. "

1. Where is the fuel pressure test fitting?
2. Where is the coil they speak of?
3. Where is the inertia switch or the fuel pump relay?
4. How do you pressurize the fuel system?

The book explains things but never gives any pictures or diagrams on where the stuff is.
I searched the technical links and found nothing.

Also, if the fuel pressure or cylindar compression was indeed low, wouldn't it throw a code? Once again...I'm new to all of this.
 

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- had 2 stage cats replaced with 1 cat
Yea Zippy he does...although when I first read the symptoms thats what I thought also...It definatly sounds like the engine is starving (but for what..air, fuel I can't figure) I do know your right about the 33's and 3:55's... I ran 38 TSL's with 3:55's for prolly 6 or 8 months and it wasn't speed racer by a long shot but it didn't bog down like that and I was runnin' a 5.0 :shrug
 

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What was wrong with the cats? Were they "broke"? You may have parts of them in your muffler causing excessive backpressure. I dont know if this would give you low readings on a compression tester. I know from experience that this will cause the EXACT problems you describe. Try unhooking your exhaust before the cat and see if this makes a difference. With that kind of compression you should be blowing smoke out the pipes though. Just doesnt make much sense yet. Keep us updated :uhoh3
 

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The muffler shop said the cats were intermittantly plugged/unplugged. There was also a massive exhaust leak just before the 1st cat that was fixed.

Every once in a while I smell something a little smokey when driving. I wouldn't say it smelled like exhaust or gas....more like someone burning firewood outside. Until this morning (@ 6:30 AM) I just assumed it was someone burning something, but now I am almost positive it is comming from the truck. It is only once in a while though.

Is there ANYTHING that could possibly cause my low compression, not internal to the engine, such as a bad sensor, vacuum loss, etc?
Due to weather I didn't get a chance to check the timing this past weekend. Hopefully next weekend.

I need the Bronco in snow, but at 7 mpg the gas to and from work is killing me.
 
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Is there ANYTHING that could possibly cause my low compression, not internal to the engine, such as a bad sensor, vacuum loss, etc?
No.


Pull the valve covers and do the compression check. Look at your rockers if your concerned about the timing chain having jumped. Be sure to start at TDC and see what in thy hell is going on.

good luck.
 
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