98 Tahoe 2 door misfire.. Mechanics??

[68lemans462]

I have a '98 Tahoe 2 door with 118K - very nice truck. Orig motor/trans. Ignition system was serviced within about 15K (plugs/wires/cap/rotor). It has always ran really good. The engine has developed a miss at highway speeds in 4th gear when the engine is under light load. The engine starts fine, idles smooth and does not miss at WOT. It also does not miss while driving around town. I have also noticed that gas mileage is not improving. The check engine light has not come on. I have not checked ODB2 for codes.

I've been planning on replacing the injectors with the MFI unit, but it is possible that they were replaced by the previous owner (he was meticulous). The intake gaskets do not appear to be leaking, surprisingly... I'm wondering what could be at fault, aside from the injectors?? I was doing some reading and others suggested 02 sensors, cat converter, vac leaks, EGR valve, etc, etc... Of course, everybody says just replace the injectors. Any ideas before I go gamble $400 on the injectors??

 

[1999hoe]

perhaps a treatment of seafoam would do the trick>>>

 

[Miami-Yukon]

I'm not a mechanic but maybe a really small vacuum leak somewhere... again i'm not a mechanic... Just a thought

 

[68lemans462]

any mechanics??

 

[PH99TAHOE]

A misfire at highway speeds is typically a fault in the ignition system somewhere. It's possible there is a break somewhere on the plug wires near the boots, or something faulty in the distributor, especially if the replacements were a cheap auto parts store brand. Double check all the wires and their boots, and check the distributor. If you know someone with a TechII scan tool, that would narrow it down to which cylinder is misfiring and you can start there.

 

[ravingmadman]

Yup. My rig hiccups when I'm doing 40-50, and slightly accelerating. This isn't the engine, it's the tranny with schizophrenia trying to be in both 4th and 5th gears at the same time, and my torque converter locking and unlocking causing the lurch. it really feels like a misfire though. If your engine is misfiring, there are many sensors that would pick it up, and give you a code, with which cylinder specifically.

Go 40MPH and engage the cruise control. If it still does it, I've got nothing for you. If it doesn't do it, it isn't your engine.

 

[68lemans462]

Yup. My rig hiccups when I'm doing 40-50, and slightly accelerating. This isn't the engine, it's the tranny with schizophrenia trying to be in both 4th and 5th gears at the same time, and my torque converter locking and unlocking causing the lurch. it really feels like a misfire though. If your engine is misfiring, there are many sensors that would pick it up, and give you a code, with which cylinder specifically.

Go 40MPH and engage the cruise control. If it still does it, I've got nothing for you. If it doesn't do it, it isn't your engine.

All stock tahoe's have the 4L60-e trans which is a 4 speed, not a 5 speed...

 

[drowndindreams]

None of us can exactly say what it could be, but it doesn't have anything to do with plugs and wires and such. Your best bet is to have it checked out, and have your codes read.

Tell me this, when you come to a stop, does the car wobble/vibrate?

 

[ravingmadman]

Yup. My rig hiccups when I'm doing 40-50, and slightly accelerating. This isn't the engine, it's the tranny with schizophrenia trying to be in both 4th and 5th gears at the same time, and my torque converter locking and unlocking causing the lurch. it really feels like a misfire though. If your engine is misfiring, there are many sensors that would pick it up, and give you a code, with which cylinder specifically.

Go 40MPH and engage the cruise control. If it still does it, I've got nothing for you. If it doesn't do it, it isn't your engine.

Geeze, RM- STFU, n00b!!!! I fail. Yeah, 4-speed. Uh hurr.... And My hoe's in the shop, so I asked them for an opinion, and they said that what we're both experiencing means we need a tune up. I fail again. New plugs, wires, cap, rotor, and possibly injectors/spider if it doesn't go away. All are pretty easy to do, except those damn rear plugs... I'm batting 1000 lately. FML

 

[TheBeast99]

i still consider a 4-speed with OverDrive a 5-speed.
it's got 4 gears and OverDrive is a wicked agressive last gear that it slips into only after 4th.
but that's just a n00b computer geek's view on it. i know enough to be dangerous >:-] and stupid at the same time lol