very odd drivibility issue

[mattferkey]

Help with - very odd drivibility issue

I have a 97 ex sohc 4.0 4x4 Lately while driving at hwy speeds (65mph) my truck will loose the power to keep the truck up to speed very suddenly. I push into the gas and it seems like it is working really hard but cant maintain speed. I have to mash the pedal untill it drops a gear and regains speed. Then like a switch while accelerating, I regain all of the missing power and the truck takes off like a bat out of hell. I can also notice this coming from a stop, it will feel doggy, then like a switch was flipped, it will take off. But this only happens sometimes, say 40% of the time. Otherwise the truck is very responsive and peppy. I have always kept up on maintnence, Just cleaned the maf, replaced the pcv valve, did the seafoam treatment, and even had the pcm reflashed to the newest version. After the reflash the truck seemed even more alive than ever, but the problem still exists, and I am stumped as to what it could be. Anyone that could shed some light on this would be greatly appreciated.
thanks so much
matt

 

[ThePhoenix]

maybe a failing coil pack? guesing

 

[NOVICOUPE]

re

Check O2 sensors.My wifes X was doing same thing and then just about died coming home one night on the interstate about 1hr from home.It would run but did not even have enough power to do anything but idle..Had to get a ride home and go pick up the x next day with my car trailer.Got on here and figured out by the codes it was throwing it blew a fuse in the main fuse box in engine compt.Figured out it was problem with O2 sensor.Well front left had a heat shield hanging on wires and barelly cut through wire and was causing all the problems.Changed sensor and got rid of heat shield an the thing ran fine again. Does your check engine light come on when this problem happens.If so have the codes pulled.Hope this helps.

 

[mattferkey]

there are no codes present or in history the motor doesnt spit or sputter or run rough, it just lacks power... I am wondering if the MAF is failing and when it fails the computer goes into fail safe then the MAF sends voltage again and it kicks back into open loop
matt

 

[mattferkey]

if anyone truly understands the way a modern engine works with a pcm and sensors, please give your input. Even if you dont know what the problem is, surely there should be a way to diagnose a specific system, (intake, fuel delivery, exhaust) that the problem is mostlikely in.
thanks
matt

 

[NOVICOUPE]

re

As I stated check the o2 sensors.My wifes truck ran fine and then all of the sudden going down the road it would just kinda pooch out and lack power.Then all of the sudden it would be fine again.It did not spit or sputter or run rough either just lack power all of the sudden under driving speed and then clear up and be fine the next minute.Easy to crawl under the truck and check the wires on all the O2 sensors.If they are good then that is one thing you can know for sure is not the problem.,

 

[mattferkey]

I will look under the truck and also check o2 voltages via an obd2 scaner. Please give your feedback on other possibilities, and or solutions!
thanks
matt

 

[Mbrooks420]

Do you have access to the scanner when you drive? If so you I'd check to check if it is leaning out when the problem occurs. If so I'd suspect a fuel pressure regulator. Could also be a problem with the coil pack, I guess. I had a car that was doggy occasionally, and had trouble with hot starts. That ended up being a coil pack. I was taking my stuff to mechanics at that time, and he figured out is was the coil pack. Not sure how. I would think a bad coil pack would trigger a "misfire cylinder XX" code. How old are the plug wires?

 

[mattferkey]

the plugs and wires are about 10k miles old

 

[mattferkey]

the o2 sensors seem to be fine... when failing dont they read low voltage? not cut in and out?

 

[L4CX]

I'm not sure as to why it wouldn't happen all the time, but Sometimes when People seafoam the engine it'll mess with the Plugs. So you could check those. Also, I had a Van that would have a similar problem and eventually would only do about 35. I took it in and all they had to do was replace the Fuel filter. I would suggest it. It could be close to being plugged up and about 40% of the time something could move into the little hole remaining and cause the spiratic behavoir. The fuel filter is a Pain to get out if you don' the correct tool, but they are relitively cheap and make it a little easier. Good luck

 

[mattferkey]

i replaced the fuel filter less than 10k mi ago... i suppose i am due again... and as far as the seafoam... like you say... it doesnt make sence as to why it would only be intermettent

 

[Mbrooks420]

I wouldn't bother changing a fuel filter with 10k on it.

 

[mattferkey]

well i am usually pretty meticulious on my maintnence, and as you can immagine this problem is driving me nuts

 

[Turdle]

You might check the Throttle position sensor.

 

[mattferkey]

I will check that out. do you know what the resistance should be at idle and at wot

 

[Turdle]

You might not see it, but look for a "dead spot" or spike while you slowly actuate the throttle lever-checking resistance with the key off.

then, with the key on, check the voltage-
you want to see a steady rise with no spikes or drop out of voltage
. it should have a range from < 1v to >4v

 

[mattferkey]

very useful information.. thanks jtsmith

 

[mattferkey]

the tps has no flat or dead spots? any ideas?

 

[mattferkey]

What do you guys think about it being a thermistat... since i got the truck the coolent temp guage has read just below half... if the temp isnt getting up high enough, the truck will be running rich to warm up the motor quicker.