Random Power Drop at Highway Speed with A/C On and Try to Accelerate

Mikey1968 · Oct 31, 2006

Seems it might be the TPS as my throttle is completely improved...nice and crisp...smooth. Makes it much easier to shift. Also, tons of top end power I didn't have before. So far, no power loss hesitation, either!

Think I nailed it!
Mike

Mikey1968 · Feb 21, 2007

OK...I am reviving this thread as the silly thing is doing it AGAIN! Very rare....like once every other month. Again, no a/c on in the winter (happens with setting on Vent, no defrost).

Recap....cruising at 75mph, push slowly on the pedal to do a slow acceleration and then total loss of power....coast to 60mph and power kicks back in like nothing happened.

Things worked on....Cleaned the connectors, new fuel pump, new TPS, cleaned EGR valve and throttle plate, new EGR sensor, new distro/TFI, new fuel pump relay, cleaned MAF sensor, timed engine, pulled codes: all good, fairly new timing chain, new plugs and Ford Racing wires.

I'm stuck with living with it as it' occurs so rarely. Until it completely fails, I can't track it down....and I've run out of ideas.

Anyone help me with this one???

Thanks,
Mike

webslinger67 · Mar 20, 2007

have you tried...

check your Cats to see if they are plugged.... i have the same problem on my 90 GT .... i think its the cats....

jrichker · Mar 20, 2007

Your problem is probably electrical in nature. When it happens, check the voltmeter for unusual activity. Check to see if things like the radio or heater stop working when it happens. Top suspect is the EEC relay circuit since it would cut power to the computer and fuel system. Again, look at the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/. The diagrams will be very helpful in troubleshooting the problem.

Mikey1968 · Apr 8, 2007

I was working on the rear brakes when I noticed the fuel line coming off the fuel pump...the pressure one, was weeping at a prior splice I did when the holding strap had broken and allowed the line to contact the exhaust melting it. I have all new lines and fittings ordered from www.ronmorrisperformance.com.......Stay tuned!
Mike

Mikey1968 · Apr 18, 2007

OK...the GT really liked having new lines installed....runs like a scalded rabbit. Didn't realize the loss of power I had. Anyway, problem is still there. When it happens, the tach stays pretty close to the same rpm so I'm still thinking a fuel problem. New filter, new pump, new lines, new gas tank, new fuel neck filler pipe gasket, cleaned throttle body, cleaned EGR, cleaned MAF, cleaned 10-pins, new EGR sensor, new TPS, check fuel pressure at idle........no codes. Soooooo....now I will change the fuel pressure regulator, I guess. I searched this forum and others and that' seems to be the concensus. Stone stock.....

Wow....I looked at the first post....this is been bugging me long enough, I'd say.

Strype · Apr 18, 2007

Mikey1968 said:
I was working on the rear brakes when I noticed the fuel line coming off the fuel pump...the pressure one, was weeping at a prior splice I did when the holding strap had broken and allowed the line to contact the exhaust melting it. I have all new lines and fittings ordered from www.ronmorrisperformance.com.......Stay tuned!
Mike

Strype · Apr 18, 2007

Are you running a short Cold Air Intake by chance?

Mikey1968 · Apr 19, 2007

Nope...just a K&N in the stock housing with the silencer removed. All is stone stock with trubo mufflers. Only non-stock stuff is in the suspension and brand new T5 with a Hurst shifter. I will pickup a non-adjustable OEM-type fuel pressure regulator from NAPA this evening.

All you guys, crawl under your 'Stangs and add a couple of zip ties to hold those two fuel lines as a backup to the old original brittle plastic piece. When it breaks, it'll allow those lines to contact your exhaust and melt.

Mikey1968 · Apr 23, 2007

I bought a stock fuel pressure regulator from NAPA to put on and thought it'd take an hour or so....wrong! So I quit for now and will need to schedule a lot more time....those silly bolts are upside down! What a cluster F....!

Anyway, I went ahead and checked my fuel pressure with the old regulator on and here's what I got:

Idle - vacuum line off: 42
Idle - vacuum line on: 35-36

While out of gear - accelerated engine rpm - vacuum line on: Instant 40-42 then drop and held at 34

Key off it held 40

Looks like the pressure is a bit high. Is it normal for the pressure to spike up and then drop like that when you hit the accelerator while stopped out of gear?

Thanks,
Mike

HISSIN50 · Apr 23, 2007

Those FP numbers look alright to me. You're seeing a decent differential which indicates the FPR's diaphram is ok. It is a little high but the puter will adapt without isssue (I'd take your slightly higher pressures over slightly low pressures).

Mikey1968 · Apr 25, 2007

Soooo...do you think it's worth changing the regulator to fix that high speed hesitation? I'm running outta ideas!

Mikey1968 · Apr 25, 2007

This guy sounds like he's having a similar problem. His fuel pressure sounds low, though.....
http://forums.stangnet.com/showthread.php?t=694887&highlight=fuel+pressure

Joey5.0 · Apr 25, 2007

Very Wierd. Your problem sounds different than mine though. One night the car would just die while i was driving, and then while i was WOT the car would do nothing and then all of the sudden just kick in like Vtec Lol!

Mikey1968 · Apr 26, 2007

Yeah, I noticed it was different, just somewhat similar. Your WOT problem sounds about the same. Power drop off at 75 mph down to 60 when I mash the pedal, then kick back in like nothing happened.

My problem occurs very rarely (once a month) but when it does, the conditions are always exactly the same....going uphill in 5th and mash pedal.

So far, every 5.0L expert is at a loss.

Did you ever fix yours?

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