Strange power loss problem when cruising

[stevetatro]

What's up everybody.

The past couple of days more normally dependable '93 SHO has been acting funny. Let me try to describe the symptoms and hopefully someone can help!

When cruising on the interstate, all of a sudden the RPMs will drop. Usually at 80mph the engine's turning at about 2800. All of a sudden the RPMs will drop to about 1500 for no apparent reason. This has happened at a few different speeds, 80mph, 70mph and last night (in the snow) at 55mph. When it happens, there's obviously a severe lack of power. Push the accelerator a little and there's no response. Then all of a sudden, after 5-10 seconds, it'll come back to life and be just fine.

Any ideas? The car has been pretty well maintained over it's almost 200k mile life, although now that I think about it the last 60k service was 72k ago. The ATX was replaced about 60k ago and hasn't given me a problem. There's been a leak from the rear main seal for about 5 years now, but it doesn't concern me too much! The one job I keep telling myself I need to do is the rod bearings - they're original.

Oh, and I forgot to mention, there's no CE light when this happens. It just chugs along and then periodically wakes up for a few seconds.

Anybody have any thoughts?

Thanks,

 

[93rev2sev]

You sir, need a crank sensor.

 

[SolidState]

not necessarily.

being that this is an ATX, the tach dropping is the engine taking the load off of the torque converter, but the wheels are keeping the engine turn.

I am betting this is the same problem I had last week. Being that there are no idiot lights popping up and the tach still works, this is likely a fuel related issue.

I traced my problem (with the help of 93rev2sev) to a severely corroded plug causing a short in the fuel pump power circuit.

The fuel pump power circuit travels from the CCRM (on the rad support) splits off and heads to the PCM and then through the firewall on the driver's side. It travels to the back of the car to the Inertia Switch located behind the carpet on the driver's side fender support. From there, it travels back along the driver's side of the car to a GREEN plug just in front of the trunk/fuel release levers under the main harness. In this area is also the GROUND for the fuel pump. From there it crosses the car to passenger side just in front of the front seats, then heads back along the passenger side to the fuel pump.

The problem with all Taurii driven regularily in the winter is that water and salt dragged in by the driver soaks through the carpet and waterlogs this area. The plug and ground tend to corrode.

At first, my problem was intermittent, then all of a sudden it shut off. It may not have been that the wires were completely broken, but there was enough resistance due to the corrosion to keep the fuel pump from running.

Pull up the carpet and look for water.

 

[stevetatro]

You sir, need a crank sensor.

It wouldn't surprise me, my CPS is original. But so is my fuel pump. And a host of other parts!

I guess I'm wondering how confident you are in your answer? Also, I thought the CPS would leave me a nice 3-digit code and throw on my light?

Thanks for the help.

 

[SolidState]

the CPS is a very simple device and doesn't fail unless something causes it to fail, like a waterpump leaking on it.

I will tell you this...when hunting down fuel related problems, the access door cut into the body under the seats was uber-valuable!

 

[Shopower400]

Sounds like a fuel pump! Had kinda the same prob, only mine "chuggd' out all the way to 0! I would say yuor CPS is the coulprit, but since you mentioned this also happened when it was snowing makes it less likely that coolant was dripping onto it from the waterpump (but not totally out of the question either.) I would lean more towards the pump. Try changing your fuel filter first. If the pump quiets down considerablely & you notice an improvement in performance then you may have found your prob! If not you'll have to keep looking. At least the fuel filter is a cheap way to help steer you in the right direction

 

[SolidState]

while changing the fuel filter can't hurt, a fuel filter isn't going to cause an intermittent failure.

 

[93rev2sev]

I guess I'm wondering how confident you are in your answer? Also, I thought the CPS would leave me a nice 3-digit code and throw on my light?

Thanks for the help.

Weather it's the problem or not dosent matter. If the Crank Sensor is original, I would not perform any other work until I did a front 60k (I don't consider cleaning the MAF to be "work")

Timing belt - $18 Rockauto
Crank sensor- $37 Autozone
Cam seals- $15 Timkin 1213n (anywhere)
Front main seal -$7 Rockauto
Water pump - $48 Rockauto

$125+ shipping/tax/supplies and lots of work.

 

[Arc Angel]

I have to join in on this post and the same problem. I've got a 94 ATX with the identical problem. Mine only happens when I'm climbing any type of a grade, though. Riding at any highway speed, once climbing a hill (ANY degree vs. flat), the car looses power. Stepping further onto the accelerator pedal does no good. But, let up on the pedal for a second, and then press back down on the pedal, and it takes right off, fine. Five or six seconds later, it looses power, again. Does this over and over, with the same 5 - 6 second interval in between power losses, RPM's drop about 2 - 300 RPM.
It's like a nightmare trying to figure this one out...I've spent months changing everything - Crank Position Sensor, Cam Position Sensor, Fuel Pump, Fuel Filter, Plugs, Wires, Coil Pack, DIS, anything I could think of - nothing has stopped it. If someone can figure out this 5 - 6 second interval between the power loss, I think that has allot to do with it.
Frank

 

[itwonder]

I..identical problem. M...only happens when I'm climbing any type of a grade, ... the car looses power. Stepping further onto the accelerator pedal does no good. But, let up on the pedal for a second, and then press back down on the pedal, and it takes right off, fine. Five or six seconds later, it looses power, again. Does this over and over, ...RPM's drop about 2 - 300 RPM....I've spent months changing everything - Crank Position Sensor, Cam Position Sensor, Fuel Pump, Fuel Filter, Plugs, Wires, Coil Pack, DIS,

Did you change the fuel pressure regulator? Also, for grins try loosening your fuel cap when this happens and run with it loose for a while to see if perhaps there is a venting issue.

 

[SolidState]

unplug the vacuum hose to the fuel regulator.

 

[Arc Angel]

Okay...I may be an aerospace engineer, but, without a service manual - I'm lost. Where exactly IS the fuel pressure regulator - heck - I might just as well replace that, as well. Thanks again...
Frank

 

[93rev2sev]

It's on the fuel rails...on top of the intake. The one in line with the fuel line is the regulator and the other one is the pulse damper...or it's the other way around...I can't recall.

However...you never mentioned cleaning the MAF element. I would do that first.

Unplug the sensor, get some security torx bits and remove the 2 screws holding the sensor to the MAF housing on the intake hose. Remove sensor from under the hood, and spray the FILIMENTS down with CRC MAF cleaner repeatedly, letting it dry in between cleanings. It should look nice and clean when you are done.

A small magnifying glass will help you inspect the filiments, don't touch them.

Reinstall MAF sensor and see if that helps.

Or...just unplug the sensor and see if THAT helps...then, if it does, clean the filiments like I outlined.

 

[itwonder]

Here it is, but X2 check out that MAF first, and also do the gas cap test.

 

[stevetatro]

Okay. I know everybody thought this was over, that my problems could be attributed to a failing crank sensor, but now I don't think so. I hadn't started it up in over a day, then when I got off work I fired it up and it was idling really low - about 500rpms. Hit the accelerator hoping to bring it back to life, and it didn't do much. So of course, I took off! On the way home it was running very low on power. And it was loud! A couple of times - for about a minute apiece - it came to life and was running at the proper rpms for the speed and acted normally when I gave it some throttle. But the rest of the time it was really struggling. So it basically limped all the way home.

Still no CE light. Actually there were no lights. I thought I might even get an oil pressure light flicker when I was idling at 500rpms, but it didn't happen.

One other note. The other day when I was checking for codes and trying to do the KOER, I never got the sensation of the poor-running engine for 6-20 seconds while the computer tried to get the sensors to reach extreme ranges (or however it's described on the SHOtimes FAQ). I thought it was strange, but all the codes I got were pretty minor.

Any help would be greatly appreciated!

 

[SolidState]

one quick and easy thing

Check the power at the fuel inertia switch. This sounds like a fueling issue. Possibly the CCRM.

 

[Arc Angel]

Stevetatro, Same problem with mine when it starts while cold...if I'm stupid enough to go out to a highway before it warms up fully, forget it. I'm dogging with no power. As soon as it warms up, full power returns. Very strange. I'm still having that same loss of power at highway speeds. Changed plugs, wires, and fuel filter (again!!!) and still the same. I'll switch out the fuel pump later in the week. And still - no CEL coming on during any of this.
I'll also switch out the fuel pressure regulator and see if that does anything. I'm going crazy trying to figure this one out... what the heck would cause that five/six second interval loss of power, let up on the gas, step back on the throttle, and power returns, then five/six seconds later, another loss of power over and over, every five/six seconds, is beyond me...!
Frank

 

[93rev2sev]

No one is going to help you if you don't do whats suggested.

clean your MAF sensor. Until the engine knows how much air is entering the engine, it's going to suck ass(every 5 or 6 seconds while it tries a new fuel curve based on the MAF sensors screwed-up readings).

 

[Arc Angel]

OK...I not only cleaned the MAF (on both SHO's), I switched the whole unit around from my good-running SHO to this one. Still has the same problem. I'm pretty darn sure it can't be spark related (unless two cylinders are cutting out), and I'm betting it's fuel delivery. So...I'll try the regulator (again) and see what happens.
Now...out a limb with this question, but, I am running SHO-Bros. Cat-less Y-pipes and an entire Borla SS exhaust system... anyone got a bigger Throttle body/MAF they want to sell?
Frank

 

[93rev2sev]

OK time to list all of your "non-stock" parts.