1993 power loss and wont run right

[rhauf]

my '93 (220k miles) had been running great until it blew a head gasket a few months ago, i pulled the engine, changed the gaskets, timing chain and other nick nacks and put it back in. now however, it has a drivability issue that i can't figure out.

at full throttle it seems to run fine. at idle it idle fine, but sometimes drops to a slightly lower (and rougher) idle speed. when it does this i notice a slight "puffing" from the exhaust.

when driving it, if i lock it in gear so it wont shift (say first or second, for a controlled test) and slowly press the gas down, it hits a point, at near WOT where suddenly it feels as if it has downshifted, and there is instantly about a doubling in power output.. i have swapped the MAF, TPS, and engine temp sensor, with no change in conditions so far.

any help is much appreciated as it's been parked for a month and it for driving.

Thanks,

Ryan

 

[wood1]

When was the last time you replaced your plugs/wires? Pretty easy to check the wires, spray salt water on them at night and watch for sparks

 

[rhauf]

Installed new motorcraft plugs and bosch wires around 4 months ago.

before changing the head gaskets it ran perfectly, aside from loosing coolant at an increasing rate out the exhaust.

 

[wood1]

plugged converter maybe or does it seem more like an ignition problem?

 

[rhauf]

plugged cat did cross my mind... because of the possibility of cat damage from coolant going through it before the gasket swap.

but would it still seem to run good at WOT with a clogged cat? it seems to me like it'd be the opposite. Im hoping for some other things to try before i take a sawzall to the exhaust

 

[wood1]

That's what I was thinking, coolant wrecking the cat but I guess the amount of exhaust gas it would flow would depend on how fouled it was. Was thinking about fouled O2 sensor too but it wouldn't have that big of an effect. Not sure, just throwing some ideas at you. I'm still betting it's an ignition component.

 

[rhauf]

ignition yes maybe.. but where to start?

 

[MrShorty]

I would probably pull codes from the computer. Even if the CEL hasn't come on, sometimes, you will find codes in memory that will give you a direction.

I would also probably put a fuel pressure gauge on it and see if fuel delivery is doing something differently when it is and isn't running right.

 

[Turdle]

Make sure you have vacuum to the FPR ---pull the line and verify vacuum is reaching that point , at the same time smell for gas in the vacuum line.

 

[wood1]

Did you get the firing order right? I know, a bit basic and you probably checked it already 4 times... codes might tell you something as stated in the earlier post. Did you try pulling plug wires when it's chugging at idle to see if you have a dead cylinder?

 

[rhauf]

Alright now ive got something to go on again, thanks for the tips guys i'll give those things a try and get back with the results.

 

[rhauf]

firing order is correct
compression is good
fuel pressure is good.

i pulled the exhaust system out and cut out the cats today.. to discover that the first cat had decintegrated and clogged up the second cat... replaced them, and put it back together. it runs a little better now but still considerably less power than normal.

it still has a point (about 3/4 of the way down with the gas pedal) where it suddenly has more power "all at once"

 

[wood1]

Codes?

 

[Roadrunner777]

One thing I can think of, easy to test too... throttle position sensor. Here's a thread on testing:

http://www.explorerforum.com/forums/showthread.php?t=263699&highlight=test+throttle+position+sensor

 

[rhauf]

Wow, I just stumbled onto my own old thread while googling for something else completely!!

I see I never posted what the fix ultimately was for this problem.. well better late than never!

Eventually scanned it and found a lean condition for one bank, and a rich condition for the other... It turned out when I did the head gaskets I accidentally got the O2 sensors swapped (my X has the dual O2's, one after each manifold output) and that through everything way out of whack! I switched them back and it's ran great ever since.

 

[Turdle]

Thanks for updating this. Although I probably would have made the same mistake no doubt, it would be a long time before anyone would have suggested that. Glad you sorted it out!