I'm still on the quest to get my LT1 running right. Ever since doing headers last summer I've run into several problems. Here's what I'm dealing with now...

I replaced my plugs and wires a few weeks ago. Some of the plugs had the gap blown out and I had a severely burned wire. I put on a set of MSD street fire wires, platinum ac delco spark plugs and I added high temp heat sleeves to protect the wires. I also got my pcm tuned by pcm for less.

after getting everything bolted back up, it ran great. real fast and pulled nicely for the first time in months. I thought I noticed a slight hiccup under load at light throttle ( between 1000-25000 RPMs while cruising) but I figured it was just in my head but lately it's been getting worse.

Yesterday I ran the car for about 8 hours straight (a lot of turning off and starting again, maybe 30 stops total) and the more i was on the road, the less it seemed to perform like it should. After a few WOT runs I noticed it runs real crappy immediately after. The engine would shake and seem to miss. When its warm it seems to drive worse as well.

Today I used freescan for a little. Right away I got code 18. It's been an intermittent code I've been dealing with for sometime now. When I clear the codes on freescan and wiggle my injectors it goes away, but the fact it's still popping up bothers me.

I also got a decent amount of KR today. When I rev it up I get between 1-3 knock counts and after a few WOT runs I noticed upwards of 7 knock counts.

I will note that I'm getting some real bad vibrations from my headers and exhaust. It feels the worst in drive idling. It will be real bad against the floor right under me but I never see any knock when that happens.

I also have a ticking noise from my passenger side that gets worse the hotter it is. i thought it was lifters but I ran the car with no belt and the ticking stopped so it's something within the belt assembly.

So I'm chasing knock and a phantom bad injector. I have the Lt-4 knock module too. I feel like it might be detonation but I'm not too familiar with it other than it's one of the worst things for an engine

any ideas?

 

I'm going to try tackling the exhaust rattle this weekend. I got some high temp resistant silicone sponge I'm going to wedge between the floor and the exhaust to absorb the vibration. and if that doesn't take care of the vibrations I'll probably be looking at some poly motor mounts in the future.

I'm also going to try some octane booster to see if that helps in the event it is actually detonation

 

Is your exhaust touching? I would look at your hangers on it. What I have found to be good is a solid hanger on the pipe that goes up and is caught in a rubber mount sleeved in metal. I have little luck with the hanger straps that have rubber riveted. Hanging the exhauat is important because it needs a level of flex and still retain strength. Also curious what you meant about the spark plug gap being blown out. If you havent spaced the coil and icm off the head it may be worth a try because heat soak can effect them.


Posted from Camaroz28.com App for Android

 

If any of the exhaust is touching or vibrating against the body(or other parts of the car), may be causing the knock sensor to trigger.

 

Yeah I've got some bad rattles and vibrations where it touches the floor but I've seen a lot of posts with people saying it's to be expected with these cars. that the bad vibrations and the engine shaking are just a part of owning an lt1 with headers.

I drove it around a little tonight and when I go WOT it runs like absolute crap after. It shakes bad and feels like its missing. I assume that's characteristic of knock causing timing to be pulled and the loss of power that goes with it.

 

The effects of knock retard quickly dissipate. It should not run poorly afterwards (unless the condition causing the KR is still there).

You also say you are getting some minor knock counts. That does not mean you are getting KR. You need to see what the KR register is saying.

 

I think you are referring to "degrees retard", but calling it "knock counts".

Bad vibrations, engine shaking, and the headers hitting the floor is not "part of owning an LT1 with headers". Where did you read that?

Sounds like you may have an engine overheating problem, with the heat causing loss of power, and affecting parts that can heat soak, like the ICM and possibly the optical cam position sensor in the distributor.

What have you done to try and eliminate DTC 18. The only possible components that could cause the code are the injectors, the wiring and the drivers in the PCM. You indicate the code goes away when you jiggle the wires. Have you checked the resistance of the injectors (12-16 ohms)? Have you verified 12V at all times at the pink wire on each injector harness connector? Have you tested the injectors while they are extremely hot - another possible heat soak problem.

 

Yes, when I said knock count I meant instances of knock retard. I'm getting a lot more knock counts but only a few instances of knock retard which i noted above.

I've just seen among random posts that vibrations here and there are something that isn't out of the ordinary. I've looked through several threads about exhaust vibrations and motor mount replacement and it seems to be a common occurrence, but probably not to the extent I'm getting with mine.

I feel like you might be onto something with the overheating idea. My thermostat on the dash never really gets above 180, only on hotter days but I feel like the heat soak could be an issue especially with the headers.


And as far as the code 18, i first noticed it a few months ago. it comes and goes which is frustrating because I thought it went away completely. hopefully i can look into it more if i can get my hands on a volt meter. I'm taking it to a shop on tuesday to have my A/c lines evacuated so ill see what they say about the issues i'm dealing with and can maybe test a few things for me.

 

update:

I figured out which injector was bad. I'm almost positive it's the injector on cylinder # 1. I noticed the wire was kind of sliced near the connector. when I wiggle it, it sets off code 18 on freescan so that has to be it. I can tell when it's not functioning right because the car shakes more and the throttle response is crappy. I wrapped it in electrical tape but it still comes and goes.

What I'm confused is when it's running well and the injector is working, when I go WOT or I pull a fast tight turn, all of a sudden its running crappy again just like the injector decided to cut out. why would this be?

and I'm still getting knock retard (still think its from my exhaust rattle/shaking, especially when I'm at WOT)

 

Keep in mind if enough strands of wire were cut(on the wire you found) you may not be getting the voltage you need.


Posted from Camaroz28.com App for Android

 

are you running premium fuel all the time? For me with the kr I would want to know for sure if its false or not and therefore I would be certain my fuel has enough octane. I would consult someone with more experience with me and see if you should add a little av gas or race fuel to up your octane and see if it remains or dissapears. If thats safe, wise, and what percentage to add is all something I dont know but its what I would question if I had kr. Might just be time to get your injectors cleaned and checked out. I know on my stock setup with 135000 I had bigtime improvements with new wires,plugs ,and clean injectors.


Posted from Camaroz28.com App for Android

 

I did add some race fuel but I'm still getting timing retard.


And the wires aren't sliced, it's just the outer plastic of the wire. Its still causing a problem though

 

If you have an injector that isn't delivering as much fuel as it's supposed to, you may have detonation on that cylinder.

And if one cylinder is running lean, the O2 sensor picks up the lean condition, and the PCM addes extra fuel to the entire bank, so now you have 1 cylinder running not quite as lean, and 3 cylinders running rich. Not going to run well at WOT under those conditions.

 

I believe I have it sorted out for the time being. I wrapped the exposed wire in hi temp vulcanizing tape, and then covered both wires for added protection. I drove it around for a bit today with freescan and code 18 never came back up, even with my foot into it. I'm assuming this should take care of it because none of the actual wires were damaged, just the outer plastic.

In the event my fix doesn't completely do away with what I'm dealing with, what's my next option? I know it's possible to purchase another connector, but I'm quite the novice when it comes to wiring, splicing, etc..

And I'm wondering why the code was so intermittent. At WOT, I assume there's more electrical current running to the injectors and the exposed wires caused couldn't contain it? And then driving for longer periods of time, the heat soaked engine bay probably caused an issue as well?

 

how would I go about replacing the clip that's faulty?