"SHOTIME" power loss @81,000 miles???

[TYM2SPD420]

I have a 95 ATX that does not have the power it use to. At 4000RPM it doesn't take off like it use to and the secondary runners aren't as loud. The butterfly valves open and close and I can hear the secondary runners but just lags and seems to stumble (not a lot just a little). Sometimes it seems to pull fine and run great but it might be my imagination.

I just bought a 93 ATX "parts car" for less than $500 with 200,000 miles, engine knock, slipping transmission, and its faster than my 95 ATX with 81,000 miles. I have replaced the plugs and wires, valve cover gaskets, water pump and a few other items. I don't know what would cause this issue. Any idea's would be great.

 

[1993MTXSHO]

I have no idea but I swear to god all the cars getting parted seem to be faster then the ones that are still on the road.

 

[1bad98SHO]

Does the engine knock any? Could be crank cancer. You may also have a clogged catalytic converter.

 

[TYM2SPD420]

Engine doesn't knock and I should check the cats. It has 81,000 miles and i have kept up on engine maintenance (new plugs, wires, valve cover gaskets, starter, H20 pump).

How does the intake work exactly? I can't find any good diagrams or anything.

 

[tardboy21]

Engine doesn't knock and I should check the cats. It has 81,000 miles and i have kept up on engine maintenance (new plugs, wires, valve cover gaskets, starter, H20 pump).

How does the intake work exactly? I can't find any good diagrams or anything.

long tubes are primary runners, and there are flappers (connected by a rod on each side) inside the secondary runners (the short elbows) that open at 4k. They meet at two separate openings in the head.
If you have a parts car, take the intake off and clean it. They get some carbon build up in there.

 

[jmpSHO]

Sounds like a bad cat.

 

[SHO_91]

Could be bad timing or that the car retards timing (knock sensor, SPOUT signal). Have you pulled the codes yet?

 

[TYM2SPD420]

Could be bad timing or that the car retards timing (knock sensor, SPOUT signal). Have you pulled the codes yet?

Need to pull codes still. it seems to be more sluggish when i first start the car and take off but that might be because the engine is cold...?

 

[TYM2SPD420]

UPDATE: Good news! My SHO is back... for the most part. I pulled the codes myself with the help of this site http://www.shophoenixproject.com/eec/eec.htm and checked the codes through this site http://www.shophoenixproject.com/eec/code3.htm.

Codes that came up first time pulled:

111 - system check OK
136 - O2 sensor not switching/ running lean
157 - Mass Air Flow signal is/was low or grounded
225 - Knock sensor not tested (ignore if not pinging) *car does not ping that I can tell*

I took the MAF out of my 93 and installed it in my 95. COULD NOT BELIEVE THE DIFFERENCE!!! The car pulls so hard it will smoke the tires again

After I replaced that, I pulled the codes again. This time i got: 111, 112, 136, and 411. It pulled 2 other codes that I think I wrote down wrong (438 and 413). I double checked the "438" code and realized I missed one CEL blink. It was "538" or code for "system did not receive 'Goose' test". So if I can't count and "413" should be "513" then that means "Replace processor (PCM) (internal failure)". oh, and "112" was for my IAT sensor which I also replaced after pulling these codes.

Now the car runs great again. The secondary runners that should open @4,000rpm don't sound as loud and I don't feel that lil extra pull at 4,000rpm but its fast all the way til redline... How do you properly check to see if the runners open?

Also, since my O2 sensors are "not switching/ running lean", I want to revive my exhaust system. Any suggestions? I was thinking about cutting the cats off (sure those puppies are going. 81,000 miles and never replaced) and straight-piping from down pipe back. Not sure if this is a good idea but that's why I'm asking the experts.

Thanks again for all the help!!

 

[goalieman59]

Great way to revive your system. SHO Source

 

[SHO_91]

To check if the secondaries' butterflies open:
Open hood, ignition off. Make a mental note of the position of the 2 small levers that you can see around the mid-section on top of the intake. This is the OPEN position.
Start car. Look at the position of the levers again. It should be different. This is the CLOSED position. They will open at around 4k rpm. I guess you can't rev an ATX in Park without hitting the rev limiter...

 

[Racer X]

You can just start the car, and disconnect the runner control solenoid at the rear of the manifold. Disconnecting the solenoid should open both sets of butterflies. Plugging it in will close the runner butterflies.

 

[SHOtimer]

Also, since my O2 sensors are "not switching/ running lean", I want to revive my exhaust system. Any suggestions? I was thinking about cutting the cats off (sure those puppies are going. 81,000 miles and never replaced) and straight-piping from down pipe back. Not sure if this is a good idea but that's why I'm asking the experts.

Thanks again for all the help!!

I just had my SHO smogged today, and it passed w/ flying colors. It has the original cats with 230k. Your cats should be fine with only 81k.

You just need two new oxygen sensors. Buy the bosch ones, and you will be on your way. You don't need a new exhaust system.

Doug

 

[shobote]

I just had my SHO smogged today, and it passed w/ flying colors. It has the original cats with 230k. Your cats should be fine with only 81k.

You just need two new oxygen sensors. Buy the bosch ones, and you will be on your way. You don't need a new exhaust system.

Doug

yup; 81k is very low mileage; if your stock exhaust is not leaking, a new catback will just empty your wallet, rust out in about 3 years, and not gain anything performance wise.

 

[TYM2SPD420]

yup; 81k is very low mileage; if your stock exhaust is not leaking, a new catback will just empty your wallet, rust out in about 3 years, and not gain anything performance wise.

Good to know about the cats. I have been looking into just replacing some of the piping with a new muffler (one in: two out) so I can keep the dual pipe look. I love it. I was thinking about using Marauder "look-a-like" tail pipes or something like that.

I have about $500 to do whatever I want to my SHO for fun. What do you recommend?

 

[SHOtimer]

If it were my car?

I'd replace the o2 sensors, do a '96 brake upgrade. If your suspension is original I'd look into replacing the struts/bushings/tie rods, ball joints...and so forth.

I'd also make sure I the tranny was serviced and I'd add a tranny cooler.

-at that point your out of money. But, have a great SHO.

Doug