Loss of power at high rpm

[Jherico Earl]

Okay so here it goes... I've owned my 1993 SHO mtx for almost 2 years now and I've tried absolutely everything to make it run correctly with no luck. Mods: magnaflow Y pipe with cats removed, 3" cat back to 2.5" duals with mustang GT mufflers (sounds great by the way) all mods done while car was still having problems while trying to make the car run right.not efficient I know hahaha. I've replaced: O2 sensors, MAF, tps, crank position sensor, cam position sensor, ignition module, all plugs, all wires, fuel pump, fuel filter, all brand new fuel injectors, ran sea foam through brake booster vacuum line, removed catalytic converters (they were fine) and nothing has made the slightest bit of difference. There is no CEL I do understand this is not the way to diagnose a problem (but really, what else could keep me occupied while I was away from home while in the military lol I guess peace of mind that nearly every sensor is new) I hope to gain some insight from any of you guys. The car has always always started, and idles fine, no strange noises whatsoever. Runs very smooth. No smoke, no real "bucking" but trying to accelerate while on the highway at higher rpm, let's say anywhere above 3300 rpm, you can feel, I could call it, "uneven power" but no misfiring whatsoever. Very very subtle "bucking" you could say. Most people probably wouldn't even be able to notice it. Maybe fuel pressure regulator or alternator could be the issue? Checked fuel pressure at the rail after pump/filter/injectors were replaced and it was all up to par. Car doesn't burn oil. I don't know if I'm missing any info but if y'all have any questions, I'll most definitely answer them. I want to get it running correctly to give my 2003 wrx a run for the money haha I know what these cars potential is, and mine doesn't have it at the moment.

 

[SHOdded]

When you say no CEL, did you also pull codes? 3 digit codes for 1992-1995 ECUs. How to:
http://web.archive.org/web/20090917070939/http://www.shophoenixproject.com/eec/eec.htm
http://web.archive.org/web/20090429123516/http://www.shophoenixproject.com/eec/code3.htm

The butterflies are common issue around 4000 rpm, but you could also have a vacuum leak/loose or cracked hose somewhere. If you have taken the intake manifold off, pinched wiring is a risk on reinstall.

The FRP is near/at the front left side of the intake (passenger side), you can check to see if there is fuel in the return line there, indicating a ruptured diaphragm. Since the problem is not manifesting throughout the rpm range, may not be easy to diagnose.

A voltmeter is your friend (in addition to checking visually) when it comes to alternator, battery, and wiring in between. Do the inside lights or headlights brighten when you rev the engine? There could be a voltage regulation issue.

What injectors do you have currently in the car? Are they OEM/Motorcraft or ...?

 

[sperold]

Timing belt is out a tooth, probably due to installation error when belt was last changed.

Or, the butterflies are not opening which inhibit the high end runners from being engaged. Find out how to manually open the butterflies and wire them open. Then, ignoring all the issues you may encounter at your lower speed, see if it has that same sensation at the 3500 rpm range.

 

[Jherico Earl]

Injectors and o-rings are OEM new. I have had the intake manifold off and reinstalled with new gasket and I am sure there is no pinched wiring, I was careful on that part. The secondaries open at about 4050 rpm without a doubt, I can hear it when trying to accelerate for sure. I will pull codes here in a little bit now that I know how, thank you for that link by the way!

As for the timing belt, it's worth a check to see if it's not lined up properly but I may recall having checked it before? I'm not sure, I could check again. The thing is, the car runs fantastic and has all the low end torque it should have until the engine rpm increases and it never misfires/backfires/pops at all. Still worth a check! Thanks guys, I'll check the couple mentioned things out and get back to ya

 

[Jherico Earl]

Also, all the lights are a consistent brightness and only dim if the car is just about to stall out (we're all noobs sometimes, stalls still happen lol)

 

[Jherico Earl]

Okay so did the scan... Found the culprit most likely. KOEO test showed a 219, SPOUT circuit failure, timing defaulted to 10 degrees, and a 524, Problem in low speed fuel pump circuit -Power / Fuel Pump Circuits. KOER codes are 213, (R) Ignition SPOUT or SAW circuit open or shorted - Ignition Systems and 225, (R) Knock sensor not tested (ignore if not pinging) . The one that is getting me is that DANG TIMING defaulted to 10 degrees. That's exactly what it feels like. Any ideas how to fix this??

 

[sperold]

Your car has a spout "connector" that can be removed to do the timing ritual. It is a plastic cap like thing located on the passenger side cowl area under your hood. It is low on the cowl and can sometimes be hard to find. There is a thread that will help.

http://www.shoforum.com/index.php?threads/how-to-pull-the-spout-connector-with-pics.56278/

 

[Jherico Earl]

Got it. The spout connector was actually gone. Went to the dealership and picked one up for $14. That's why my car felt like it had about 100 horsepower lol. Is it just a jumper or is it a resistor of some type? And is there only one spout? Car runs much much better now. Took so dang long to figure this issue out..

 

[Jherico Earl]

And what do you mean by "timing ritual"??

 

[sperold]

There are 2 spout connectors, but I have never seen the other one which is located near the front of the car under the hood.
It simply connects the 2 wires that lead to the connector (thus completes the circuit) and there is no resistor or anything like that.
Pulling the spout simply opens a circuit, it is like turning a switch to "off".

The timing ritual is: you pull the spout connector, find #1 plug wire, plug in your timing light, start the car, shine the light on your front damper and the stationary pointer should be pointing to the 10 degree line on your crank damper.

Usually a car with the spout connector disconnected runs sluggish all through the rpm range, not just at 3500 rpm.

 

[luigisho]

People often pull the SPOUT connector to pass emissions if those are implemented in your area. Could be it never got put back. Maybe. Also info for the brain bank if you have testing in your area and have a hard time passing.

 

[rubydist]

also, the 524 gets set any time you stall the engine, so you can disregard that code.

 

[Jherico Earl]

Thanks for all the responses guys, I'm glad I got this thing finally running correctly, I think... Lol time will tell. If I have any more questions on anything I'll search the forums, and if I can't find anything I'll make a post. Thanks guys!