91 Spirit R/T down on power

[HSKR]

Need some help. Recently returned from a drive from Eastern Nebraska to SW Colorado and back for Christmas. Car did great the whole drive until the last fill up coming home. That last tank of gas resulted in 17mpg and the car would not hold cruise anymore. At first I thought it was because I was driving into a head wind, but the drive to work and back last night the car was doing same thing. You have to go into boost to maintain speed going up hill. Never had to do that before. Its almost like there is something holding the car back. Acceleration from a stop seems normal. Goes into boost, will spin the tires, blow off valve functions. Might take a little more pedal to get up to speed, but really hard to tell as roads are crap right now. It was like a switch got flipped with that last tank of gas on the drive. When you try to set cruise, it won't hold the speed and seems as if the cruise is surging trying to. Like it will pull on gas, then let off all the while the speed keeps dropping. Used to be able to pull up hills and not have to get above 2psi of vacuum. Now I'm having to get 1-2psi into boost. And I have filled up with fresh gas last night so I don't think it's the fuel.

[cordes]

Do you have a cat on the car? I would verify that there is not a restriction on the inlet side of the turbo or in the exhaust. Next, I would check the fuel pressure. After that it gets into the cam timing and compression in my book.

[HSKR]

No cat, and builds boost fine, so wouldnt think an intake restriction. Exhaust restriction was first thing I thought, but like I said, no cat, and feels like good exhaust pressure coming out of tailpipe at idle.

[supercrackerbox]

Any noticeable change in the sound from the turbo or exhaust? Initially I'd think an intercooler pipe has come loose, although I'm not sure that would explain the lack of cruise control. A loose vacuum line however, could explain both.

[chromguy]

In troubleshooting, your current problem is predominately "the thing you changed last". This works 90%+ of the time in my industry (scientific instruments). Like a switch is a great clue, since this happened after the fuel fill therefore any non fuel related issues are coincidental (BTW,still as possibility, of course).
Have you check your codes?
like Cordes says, fuel pressure is a good check as crap in fuel such as particulates may cause issues. You could also check O2 sensor output.

Something similar to your symptoms happened to my 87 approx. 6 months ago and a simple disconnection of the negative battery terminal for a moment to reset the ecu helped for a week or so. Ultimately a new O2 sensor fixed the problem but only once did I catch a O2 sensor code but it had a map and air temp code at the same time. At some point even after resetting the ecu, the AC would run and the internal on/off switch was non functional, my gas mileage suffered even more. The new O2 sensor drove the gremlins away never to reappear at least thus far and gas mileage return to normal.

[rx2mazda]

Had this happen to me and it was a bad 02 sensor also.

[HSKR]

Only code is code 41 for alternator feikd current. Havnt gotten time to check vacuum lines, but last time I had a vacuum leak due to broken line it screwed with my boost gauge readings and my bov operation. O2 is only aboht a year old, but I guess that doesn't mean it couldn't have gone bad. Taking all theories into consideration.

A/F ratios are good on my wideband, even under boost, so I don't think it's fuel related.

[dwh4784]

Totally different avenue but maybe a wheel bearing? You should be able to tell fairly easily if one of them is producing nuclear heat after driving it. That could be holding the car back as you describe.

[HSKR]

Totally different avenue but maybe a wheel bearing? You should be able to tell fairly easily if one of them is producing nuclear heat after driving it. That could be holding the car back as you describe.

That was on my mind as a possibility.

[4 l-bodies]

Totally different avenue but maybe a wheel bearing? You should be able to tell fairly easily if one of them is producing nuclear heat after driving it. That could be holding the car back as you describe.

Could also be stuck caliper(s) or collapsed flex hose which could in turn take out a wheel bearing from the heat generated.
Todd

[HSKR]

Only thing keeping me from exploring wheel bearing or brake more is it usually results in a slight pull to the side that is bad, or some odd noises, none of which I have,

[Force Fed Mopar]

My van had a dragging caliper that never caused a pull.

[cordes]

My van had a dragging caliper that never caused a pull.

I've had that many times too. It would only induce a brief pull when stabbing the brakes hard in a straight line. It's easy to check for a dragging caliper as the offending wheel will be noticeably hotter.

[HSKR]

Checked all vacuum lines. Nothing noticeable for vacuum leaks. Pulled intercooler hoses, everything looks good there. TPS sensor was covered in oil from valve cover gaskets leaking so I swapped it with the TPS sensor on my on throttle body from my Daytona. I also replaced the valve cover gaskets and fill cap to prevent further leaks. Also pulled neg cable off battery to reset SBEC to see if that changes anything.

Will jack up front end and see if I can feel any drag on wheels.

[chromguy]

Happy New Year. I hope you find the issue soon.
Keep us in the loop, I am on edge to hear the solution.

[HSKR]

Since I was in the mood for working on the car, I replaced the alternator as well to hopefully keep the 41 code away. Had a 136amp alternator off a 98 Dakota R/T that bolted right on. Only difference we it has a 7-rib pulley on it vs the 6-rib. Just means the outside rib isn't getting used. Tried starting it, ran like crap had check engine light. Popped code 13, discovered I had knocked the vacuum line off the solenoid for map sensor while replacing alternator. trying to get it squeazed in from top without taking anything else off car was a challenge. Then battery needed charged as it wouldn't start again and showing 9vdc on my guage.

[HSKR]

SO may have found part, or all of my problem tonight. Previous changes didn't effect anything. Pulled the plugs tonight to look at them and see if they showed anything. Other than actually being cleaner looking than I expected with burning 1qt of oil every 1000 miles, I discovered the gap was at .045. I remember opening them up slightly the last time I gapped them to see if it would help gas mileage any, but thought I had taken them to .040. Anyway, closed them back up to .035, cleaned up the holes from the leaking valve cover gaskets, and threw them back in. Car started up faster and idle seemed smoother right off the bat. Will take it out tomorrow for a drive to see if it helped any while driving.

[HSKR]

Last night before work I went through and checked every vacuum line and check valve in the vacuum lines. All were good. Hooked everything back up. On drive to work, cruise control is now working as it should, but still have to go into boost to maintain speed on interstate while going uphill, so there is still something wrong with car. It's also making a new noise above 8psi of boost. Sounds like a whistle/squeal type sound.

[supercrackerbox]

If that alternator bolted in, I think you should be able to swap pulleys if you have an impact gun.

[HSKR]

No room to get an impact on the alternator. I do have one though.