BajaRunner

Would this be considered a misfire or is it just the exhaust making the noise? You can hear the hiccup when I hold it at a high idle. The engine shakes when it hiccups.

I have Downey headers, Magnaflow Cat and Flowmaster muffler with a 2" pipe all the way.

It does it in closed and open loop.

T_F_E

Is that intake noise? I get that noise in my stock intake.

2DoorRunner

Subscribed. I have the same problem. Well...its not really a problem. It has never affected me before. I just want to know what it is, and why it does it.

I have a bad injector, and one of them is noce and loud, so that has always been my guess to why it was doing it.

xxxtreme22r

I vote for a slight miss (but not really a miss more like a little bit of plug fouling), but does it do it when under load, you shouldn't have throttle open that far when at idle because it should be sending too much fuel into the motor. I know for a fact the carbed truck will, and pretty sure the efi ones do to.

BajaRunner

My first thought was an injector not doing its thing! I am still waiting for the Red Line fuel injector cleaner one of the members keeps posting about (high % of PEA)...i'm hoping it will clean it out.

If not I'll just pull the injectors. I should probably just pull them now since I have the week off. :/

Xxxtreme22r: The plugs are new, all ignition is new (except for igniter and coil). It doesn't do it under load, at least that I am aware of. I'm trying to figure out if this has any connection with my lean mixture.

2DoorRunner

Want clean injectors?
This is what you need
http://www.witchhunter.com/

xxxtreme22r

yeah could be inj's too. this is why I am glad I have a carbed truck. easier to diagnose.

myyota

Besides the noise, it sounds like your valves need to be adjusted.

BajaRunner

Gah! I just did them 2 weeks ago YOu mean they are too loose sounding or do you hear it in the exhaust? The exhaust valves were all tight so I loosened them to spec. I was just reading that some people go a little tighter though.

xxxtreme22r

if the adjuster screws are worn too much to where you can see an hourglass shaped wear mark, then you may not be able to remove the tick completely. When you adjusted them did you do it when the motor was warm or cold, or redo them again after 500 miles?

BajaRunner

There was a new head put on 4000 miles ago with the PO. I adjusted valves when the motor was as hot as I could keep it before pulling off the valve cover. So yes they were still hot to the touch. I could have adjusted them down further though. I will go back and redo 'em to double check

Exactly how tight can I make them. What feeler gauges do you use for exhaust and intake? (I used the spec's from the FSM)

myyota

Yea, they sound a little loose, but like was said above, the adjusting screws could be a little worn.

xxxtreme22r

on 92 Toy's I used what the manual called for and his has not been adjusted from cold after headgasket replace, using all original parts nothing new and his came out quieter than mine using new screws, nuts, new complete head, cam. and I never did go back in there and reset them Like he should have had me do. hmmm just said that in another thread as well. lol.

BajaRunner

Hey so can anyone answer the original question? Is this due to my exhaust setup, a lean mixture, a timing issue, or what? Its kinda pissing me off because I hate revving the engine hearing that hiccup. It makes me feel something is wrong.

I've literally done everything except pull the injectors and replace the mass air flow sensor. Everything is clean, tested or replaced... well not EVERYTHING but... any direction would be appreciated.

I'll be adjusting the valves tomorrow again... but I've had this thing before and after adjusting.

BajaRunner

Well when I disconnect the O2 sensor, this problem goes away. I also notice an increase in power. I bought an OEM replacement Denso, and it does the same thing.

My power is much better when cold or warming up. Once the ECU starts reading signals from the O2 sensor, it looses some power. I'm thinking the O2 sensors are working correctly, but the injectors or an injector is not operating correctly.

Anyone got advice?

greatskiiiier

i didnt hear anything that would raise any flags to me, maybe im missing something? but i think you're overthinking the situation and should just drive the truck until it blows up (150,000 miles down the road )

BajaRunner

Ha. You're probably right.

What makes me wonder is why the old and new O2 sensor causes the hiccup/misfire and when I disconnect it, my power comes back?!