Topic: hard time maintaining highway speed

[Clip]

I should think you could drop the exhaust pipe from the exhaust manifold and run straight pipes to check for clogged catalytic converter.  I had a similar problem with a Ford 4 banger years ago. After I replaced the head, I had no power. A bad catalytic converter was the root cause of all my problems.

[stan98tj]

im gonna pull out the O2 sensors this weekend to take a look at em because i figure they ought to be changed since the vehicle has 85k on it and they prob havent been changed. ill also try and do a vaccum check as well. im unsure at this point if any of the other sensors are faulty including the map sensor as the jeep dealership assured me they were fine, however im unsure if i can completely trust their diagnosis. as far as the timing is concerned, if the chain had slipped or stretched wouldn't i have a hard time starting the vehicle? im not too sure anymore whats goin on with this thing. i appreciate all the input, and appreciate any new input i can get. ill just have to take it one step at a time.

[aw12345]

With cases like this its always good to start wi8th the basics, and go from there if the basics are wrong everything else goes out of wack, start with the vacuum if that is low follow what I told you.
to check the timing chain you would set the timing mark on the cranck shaft pully on ) or tdc mark the rotor, now turn the engine in the opposite direction and note how many degrees you can turn it before the rotor starts to move. Anything more than 10 degrees of cranckshaft/ pulley rotation is excesive. Ignition timing is not adjustable but still would not hurt to check timing and to see if it has timing advance, also is the distributor indexed properly this affects the timing of the fuel injectors. Download the repair manual and look how to check this. I gave you the link in a previous post. It would not hurt to read through this whole manual covers testing on all engine parts as well as the engine sensors, its far cheaper to follow those procedures than just throwing parts at it.

[aw12345]

as far as testing the oxygen sensors you test those when they are installed with the engine running, the rear one has no effect what so ever on how the engine runs its there to measure catalytic converter efficiency. The front one iks used for fuel delivery corrections it should toggle between 0.1v to 0.8 volts on the sensor wire. A heated oxygen sensor generally has 3 wires a ground wire a heater wire which has 12 volts to it and a sensor wire 0.1 v to 0.8 volts if the sensor wire toggles low and high fairly quickly when the engine is running and warmed up its ok

[ron521]

I read the posts when you first melted a hole in the piston, and I am very suspicious that this may have happened as a result of something related to the new parts which were installed. In other words, what CHANGED with regards to your engine which could have contributed to the failure?

Specifically, I'm thinking that the parts guy MAY have sold an incorrect spark plug which created a hot spot on that cylinder. I've seen motorcycles burn holes in pistons from the wrong spark plugs. I recommend comparing the new plugs with each other to insure that they are all identical, and comparing them to the old plugs also (if you still have them).

As for your current low power and poor economy, again try to think of what has CHANGED since before the new piston and head...either something is obstructing air flow into or out of the engine (a rag in the air box, or something in the exhaust pipe?), or the fuel injectors are delivering WAY too much fuel, possibly because an inoperative sensor is telling them to do so. However, did the sensor fail before the hole melted in the piston, or while repairs were being made? Does the exhaust pipe appear all black and sooty on the inside? If so, your mixture is too rich. Is there any chance that a wire or vacuum hose is hooked up incorrectly, causing a sensor to operate incorrectly, or not at all? It is sometimes easy to overlook simple things...are you absolutely sure that all the plug wires are on the correct cylinders? What is your intake manifold vacuum, should be around 21"?

[stan98tj]

well all that is now behind me....a few days after i posted this topic my engine blew and i had to swap in a new long block.  all that is standing in my way of having a 100% running TJ are injectors and new rims (the ones i bought the jeep with cause the 31s to rub on the frame a bit)  Im still gettin poor mpg but i suspect that is due to old injectors that need to be changed. Im still searchin to find a cheaper way to buy them..60-70 bucks a pop is kinda steep.

As for what caused all this....the jeep always started hard from the day i got her...(had to slam down on the gas to start) we suspect the head may have had a hairline crack in it.  Suspiciously, a week after i got the jeep, i cracked the head-and yes i was running "hotter" plugs.  We suspect that the hairline crack was prob allowing antifreeze to poor down into the engine and into the oil pump and oil pan.  I bought a new head thinkin all was going to be fine but damage (possibly from the burned piston) and the antifreeze in the crack killed my oil pump and destroyed the engine while on the highway not too long after this topic was posted.  when we opened her up the #3 piston was exploded and warped...antifreeze was everywhere so i bit the bullet and bought a long block
Now things are better.

[aw12345]

Glad to hear she is alive Stan, once everything is the way it should be, take her of road and enjoy your Jeep