NOT Firing on all cylinders - Gen 2.5

[nwoods]

I have a 1998 Gen 2.5 with the 3.5L SOHC engine. I recently did the timing belt and water pump, and think it was done properly. Now about two weeks later, the truck has started to run extremely roughly, and sounds like it's firing on maybe 4 of the 6 cylinders. The engine rocks significantly in its mounts, and it struggles to idle, and as you rev it up, the vibrations decrease, but when you are driving, it bucks and is on the verge of stalling, loosing power.

One person disconnected the idle air controller harness to see what would happen, and it didn't stall, and he said that suggests a vacuum problem. I have no idea.

I know that I have a cracked exhaust header on one side (passenger side), and that the check engine light is on. Its possible the cracked exhaust header is causing the O2 sensors to throw a fault, which is causing a misfire..... but that is conjecture on my end.

What steps can I take to help diagnose where to start?

 

[BOPOH]

i highly doubt your cracked exhaust manifold would throw CEL. at one point i had both sides cracked and the heat almost melted my battery(killed it, eventually) but never a CEL. First think i would do is check codes to make sure it's misfire. If it is pull wires one at a time from coil packs and see if it affects how engine is running. Could be bad coil pack or maybe spark plugs. Another thing check your MAF, unplug and see if that change anything. These actions are by no means a solution but may help to eliminate some possibilities

 

[RyanY]

What code is the ECU giving you?

 

[nwoods]

I don't have a code reader. However, I did post a 30 second video of the engine running, sorta:
https://nwoods.smugmug.com/Other/Misc/Random/i-KFkCwRz/A

 

[ManfromSnowyRiver]

Sounds bad to me....

 

[tyty13]

Come by if you need the code reader!

 

[Salonika]

Need those codes........

 

[BOPOH]

looks like it's not firing right, does your CEL blink or just solid on? maybe a coil pack went bad or simply loose connection, each one is responsible for 2 cylinders. I'd check those, if you unplug one and nothing changes then it's bad

 

[freewayross]

Just a thought could the timing have skipped a tooth or two? Did you put the tensioner pulley at highest tension before tightening it and pulling the pin that holds the tensioner stub(the thing that pushes the pulley)

 

[RyanY]

So you have a check engine light on, which is your vehicle's way of telling you there is a problem, and generally where the problem is. Why are wasting time doing anything other than getting the code so you can diagnose the problem? The first step in your diagnosis is very clear and as easy as a trip to your local auto parts store to have them read it or to buy a code reader.

 

[nwoods]

My CEL light has been on since we got the truck. I have replaced numerous components all related to the long list of possible items provoking the CEL. I can't remember the code off the top of my head, but when I looked it up, it said "something under the hood is wrong" LOL, I swear that's what it should have said, because it was a long, long list of possible faults that was entirely unhelpful, thus, the reason why I can't remember the fault code. I've replaced the MAF sensor, the IAS controller, and the O2 sensors within the past 2 years.

 

[nwoods]

Just a thought could the timing have skipped a tooth or two? Did you put the tensioner pulley at highest tension before tightening it and pulling the pin that holds the tensioner stub(the thing that pushes the pulley)

It's entirely possible. I hope not, but its possible. When we did the timing belt, we cranked the engine a few turns and noted that the timing was one tooth off, so we reset it, and then cranked it at least 5 times around (the belt was marked and I did the count and the cranking), and it was all still properly lined up after 5 full revolutions of the timing belt. Yes, we set the tension pretty much to the max of the available travel in the pulley, and then pulled the pin on the new hydraulic tensioner. However, as IncorporatedX pointed out, it is not an OEM tensioner, but an aftermarket one.

 

[nwoods]

looks like it's not firing right, does your CEL blink or just solid on? maybe a coil pack went bad or simply loose connection, each one is responsible for 2 cylinders. I'd check those, if you unplug one and nothing changes then it's bad

CEL is solid unblinking orange, but not red. but it's been on since I first got the vehicle. I had to have the truck smogged last year, and the smog tech cleaned the MAF and cleared the code long enough to pass the test, but the CEL went back on during the short drive home. I replaced the MAF, had the shop clear the code, but it came back on right way for an unknown list of other reasons. Its at a shop today for diagnosis, when they call me for an update I'll ask what codes its throwing out now.

 

[RyanY]

The FSM has diagnostic procedures for every code that will help you determine where the problem is. Throwing parts at the vehicle because they might be related to the code is an expensive and inefficient way to repair it.

 

[nwoods]

The FSM has diagnostic procedures for every code that will help you determine where the problem is. Throwing parts at the vehicle because they might be related to the code is an expensive and inefficient way to repair it.

I completely agree. However, the FSM seems to assume that I am a factory trained, professional mechanic. It skips a lot of steps and references a lot tools and test equipment I do not have and don't even know what they look like

Some codes are less helpful than others, for example a previous code I used to get was P0306.

A code P0306 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s) Running out of fuel
Poor compression
Defective computer


Anything from a spark plug to a defective ECU. Decidedly NOT narrowing it down for me.