1998 3.5L Spark Plug Wire Troubleshooting

[Salonika]

Hey,
I am wondering if anyone has a trick for testing spark plug wires for this engine. The intake manifold blocks access to the sparkplug end of the wire so I cannot check resistance. Mitsubishi mechanics must have had a trick for doing this, I can't believe I would need to pull the manifold apart to check them.
Thanks!

 

[TheMole]

Haha yea might as well replace them and the spark plugs if they have never been replaced before. Specs are max 22 K Ohms. Are you experiencing some issues or just for preventative maintenance?

 

[nckwltn]

I've wondered the same thing myself.... the only thing I can come up with is to take off the intake manifold.

 

[Salonika]

I'm troubleshooting a minor rough idle. The wires are suspect only because im running out of other things to check. My engine was professionally rebuilt and has 10,000 trouble free miles so far. Wires on there are maybe 4yrs old but I've experienced wires failing prematurely on other vehicles. I do not have a vacuum leak, engine runs great above idle, 16/19mpg right in spec, new O2 sensors, no CEL, new fuel pump & filter & pressure regulator, swap-checked idle air motor & MAF with salvage units and it didn't change one bit, coolant temp sensor only 3yrs old, no carbon anywhere in throttle body, new EGR, new pcv, alternator and battery newer and check out ok. I'm thinking plug wires or an injector. Checking either though will involve taking truck out of service for a bit so I want to be sure it's worth it. Maybe the salvage idle air motor was also bad? The rough idle is hard to describe. It shakes the 4wd shifter so that's always a visual reference. You can also feel it in the seat. The truck doesn't stall but always leaves you thinking that it might. It occurs in P or D, but is more noticeable in D.

 

[TheMole]

How about the coil packs? They should be easily accessible.

 

[Salonika]

Good call, haven't checked those yet. Was also going to check fuel trim values with a scanner.
Thanks.

 

[Salonika]

Coil packs Primary Coil resistance was out of spec high, about 1.3 but they were hot. All three were the same way. Secondary Coils were also on the extreme high end / slight out of spec but again they were hot. Should they be in spec even if they are hot?

Fuel trims were all within a percent or two of zero both at idle and after a 15 minute highway run. This makes me think injectors are not to blame. Need more ideas!

 

[Eric M]

Coil pack resistance is given at 68F in the FSM, so I would check them again when they're cold.

 

[TheMole]

Primary Coil Resistance
Measure the resistance between the terminals for each ignition coil.
Standard value: 0.74 - 0.90 Ohm

Secondary Coil Resistance
Measure the resistance between the high-tension terminals for each ignition coil.
Measurement points
No.3 - No.6 cylinder side coil A coil
No.1 - No.4 cylinder side coil B coil
No.2 - No.5 cylinder side coil C coil
Standard value: 20.1 - 27.3 K Ohm

 

[Salonika]

Resistance values are all in spec at 68F. It's about 74 here outside and truck sat all day so close enough. I don't think the coil packs are the problem.

 

[Salonika]

Replacing cam position sensor. Many of my symptoms can be explained by a failing cam sensor according to what I've read.

 

[nckwltn]

Replacing cam position sensor. Many of my symptoms can be explained by a failing cam sensor according to what I've read.

I'm pretty sure you can get it out without having to pull the timing belt. at least I was able to remove the sensor on my 3.8L, but it's pretty much the same in that area between the 3.5 and 3.8L.... but.. you might as well do timing belt, w-pump, etc, etc, etc if it hasn't been done recently

 

[Salonika]

Replacing the cam position sensor did not fix it. After spending more time observing my fuel trim while driving around town, I'm leaning towards a leaking injector. I have negative trim (as much as 6%) in one bank at idle only. My O2 sensors are brand new so I trust what they are telling me and a leaky injector is the most likely culprit for running rich right (especially in only one bank)? I am going to do a pressure leak down test and an injector balance test if possible before tearing into it. The problem with those tests though is that I'm not sure if they will show much as I am not getting any CEL. The problem is just enough for a rough idle. I've had P0300's at highway speed in the past but they are rare. I think now that they may be related to a failing injector. I will check spark plug wires when I get into the injector job and if I find a bad one I will stop at that point.

 

[Salonika]

Picked up intake manifold gasket set today. Manifold will be pulled (plenum & upper) to get at spark plug wires for checking. Fuel injectors are coming out regardless of how the plug wires check out. Found a place that will diagnose and balance test them on the bench for $50 total. If they are dirty and can be serviced, $20 each to clean them up. If injectors and plug wires test ok I'm likely giving up and taking it to the dealer. Injectors and fuel rail are getting new seals when I re-assemble.

 

[Salonika]

Took apart intake manifold yesterday to get at fuel rail and plug wires. Took about 2.5hrs to take it all apart. All the plug wires checked out ok. Plugs looked good too. I removed the injectors and they are going out to be checked today. I have a question though for anyone who has gotten into the injectors on the 3.5, on the end of the injector that fits into the manifold (the delivery end), is there supposed to be a seal there of some kind? The FSM doesn't show one. The fit into the manifold isn't any better than "snug", hardly air tight I know that for sure, most were more like loose than snug. The end of the injector feels like hard plastic not rubber. They are 17 years old though. Seems like a perfect place for a vacuum leak to occur. Hopefully the injector shop will have some ideas as well. Thanks.