Low on power: first things

[Devin]

I for some time believed that my car is not performing anywhere near it's potential even at stock. I have never been in another SHO nor driven them so I can't base it on anything, but it just seemed less than quick. I had my brother drive it recently and he said compared to his bone stock 97 Mustang GT (4.6l) it was gutless.

With that in mind, where should I start to check for problems? I was thinking compression but in reality I don't know where to look. I don't have the CEL, but a ways back I did have some stored codes about the MAF and some other random sensors. Thoughts?

 

[jayro]

How is the maintinance? Is the clutch old/slipping? Are any calipers sticking? I would pull codes even though you dont have a CEL. If all the maintinance is up to date, try resetting the computer.

What is the tq rating on the '97 Stang? You usually feel TQ much more than HP.

 

[rubydist]

always start by pulling codes.

 

[itwonder]

Check how the engine is breathing with vacuum gauge and exhaust system checks. Walker has a good how-to video on Youtube. Make sure intake secondaries are working. Check camshaft timing. The SHO engine does not make a lot of torque down in the low revs, so don't expect too much excitement until she winds past 4,000 RPM heading towards 7.

 

[SHOtimer]

What everybody else has said is just where you should start...with the basics.

-pull codes
-what is the maintenance history, when the last 60k?
-are the secondaries open/closing when they should?
-how's the timing belt?
-fuel pressure?
-unplug the MAF, does it run better?

Doug

 

[Devin]

Thanks for the replies. I rebuilt the car back in 2008 and have only driven it 25000 miles since then. I figured the reason it wasn't running well was because I did all the work! The only things I did not do when rebuilding was the rings and the valve lash, particularly because it seemed at the time too complicated.

The secondaries are opening at 4K, there is a distinctive engine note when they do!
The clutch has 25K on it. It is the CM 1. I'm not sure what the clutch slipping would feel like.
Brakes are fine.
No idea what the fuel pressure is. I do not know what the status of the fuel pump is but could very well be the original. I have to replace the float at some point so I will probably get the kit and replace the whole thing. I have a gauge and can test this weekend.

I'll pull the codes this weekend, but I will want to reset them.

 

[jlunde15]

I'm not sure what the clutch slipping would feel like.

A slipping clutch is usually indicated by RPMs climbing while speed remains constant. Audible under full throttle when it gets baaaad.

Brakes are fine.
No idea what the fuel pressure is. I do not know what the status of the fuel pump is but could very well be the original. I have to replace the float at some point so I will probably get the kit and replace the whole thing. I have a gauge and can test this weekend.

I'll pull the codes this weekend, but I will want to reset them.

EEC Self Test Procedure <-- has instructions to pull codes, and resetting them is easy...read through, you'll find it.

Also, 3 Digit EEC Codes

Also re: replacing fuel pump: If you decide to do the floor cut method (necessary if you have SFCs), I would recommend dropping the tank a bit if you're lucky enough to have a non-rust belt car. makes having to worry about cutting the lines a non-issue.

 

[Devin]

A slipping clutch is usually indicated by RPMs climbing while speed remains constant. Audible under full throttle when it gets baaaad.

I haven't noticed that behavior, though I have heard in the past some CM clutches were slip-prone. I'll pay attention when I hammer on it this afternoon.

Also re: replacing fuel pump: If you decide to do the floor cut method (necessary if you have SFCs), I would recommend dropping the tank a bit if you're lucky enough to have a non-rust belt car. makes having to worry about cutting the lines a non-issue.

I believe it has been in the PNW most of it's life, so it should be fine. I haven't gotten under there in a while though so take it for what it is worth.

 

[jimtash]

An exhaust leak will also rob power away. Look at the doughnut where the Y-pipe meets the rest of the system for black soot. If any is present, you can be sure it's making a difference.

 

[SHOstuff]

If the feul pump is going out, would it rob it of power?

 

[Devin]

If this helps, when I go WOT and I hit 4K, the engine note changes but seat of the pants tells me nothing. When driving quick I usually shift around 6K to 2nd and again to 3rd.

 

[TopGunnYFZ]

If this helps, when I go WOT and I hit 4K, the engine note changes but seat of the pants tells me nothing. When driving quick I usually shift around 6K to 2nd and again to 3rd.

Theres a redline on the tach go to it. Also is this just a "feeling"? Its an old car with under 200 ft lbs, not saying that his mustangs any faster but driving back to back of course the mustangs going to "feel" faster.

Do the easy stuff that should be done regularly. Clean MAF, new air filter, plugs n wires if they havent been done. Next step is see what the codes say.

 

[shobote]

A stock 4.6 is only 215 HP, but it has more low end torque. C/D tested the stang at 6.6 0-60 and 15.1 in the 1/4. These numbers are virtually identical to a stock 89 SHO.

 

[Devin]

I just tested my fuel pressure KOEO. After fully depressurized it went up to around 20 and leaked down under ten. A subsequent KOEO put it around 35-40 but it then leaked down again. Is it supposed to leak down or hold steady?

 

[Devin]

Let me know if I did this wrong.

I hooked my pressure gauge up to the Schrader valve and a hand vacuum pump with an analog gauge. I connected it to the small vacuum line on the intake prior to the black canister. These are my results:

KOEO: 39-40 fuel PSI, leaked down to about twenty before I turned the key.
KOER: 30 fuel PSI @ idle, 19 vacuum PSI
KOER: 29 fuel PSI @ 3200 RPM, 21 vacuum PSI

Vacuum corrected results: 21 PSI @ idle, 19.5 PSI @ 3200 RPM

Both values were steady under KOER. Do they look right?

 

[Devin]

KOEO Codes
11
-
49
95
KOER Codes
91
18
77
74
52

 

[rubydist]

your vacuum readings are in inches of mercury, not psi - there is only 14.7 psi of air pressure at sea level, hence you cannot physically obtain vacuum of higher than 14.7 psi.

11 means the koeo test completed successfully.
49 and 95 are stored codes
49 means your spout jumper is missing or not making contact - this will result in timing of fixed 10*, which will result in a huge drop in power. this is your main issue - you need to find out why the spout connector is not being recognized by the pcm.
95 is for the fuel pump secondary circuit - this is typically a junk code set when the engine stalls for any reason. you can disregard that code for now.

91 says you are lean on the front bank - that could mean a vacuum leak or it could mean a sick 02 sensor.
18 confirms that the spout connector was seen as open during the koer test
77 results from not goosing the engine enough at the proper time during the koer test
74 results from not touching the brake pedal at the proper time during the koer test, or from a bad brake on/off switch
52 results from not turning the steering wheel at the proper time during the koer test, or from a bad pressure switch in the rack.

btw, the codes are read out from low number to high number and repeated - recording and reporting them in the order that they are presented is a useful check that you counted correctly.

 

[Devin]

I wrote them exactly as they were displayed to me. I went through each twice, so I'm not sure why they aren't reading out properly. I'll go through them again and make sure I am not missing a code sequence.

In retrospect they should be accurate since I didn't do the goose test, the BOO test or the PS test and they read out properly.

As far as the vacuum readings go, are they inaccurate or is that why the values are halved?

Thanks for the code analysis. I will look into the SPOUT issue first.

 

[Devin]

I was reading on Alldata that SPOUT is a function of the computer that is communicated to the DIS, and if that signal is missing it will run in failure mode engine management (FMEM) with the default 10 BTDC and a fixed dwell. So the failure points are the computer, the wiring, the jumper and the DIS? Is the jumper just something I can check for continuity or is there a resistor or something that actually needs a specific reading to verify it works? I so far haven't found any info on how to diagnose that part.

 

[SHOtimer]

There is also a spout connector, that if pulled will cause it to run that way.

That would be by far the easier thing to check.

It is by the cam sensor IIRC.

Doug