Misfires, Knocks, and MPGs

[gweg_b]

Hey guys, I'm back again. I feel like a nagging old person by constantly asking about these issues, but due to a recent family tragedy, I'm going to be pretty much on my own when it comes to fixing my issues, and my knowledge of automobiles is extremely limited. So, I'll probably be asking quite a bit of questions over the next few years. I'm posting here instead of my bigger project post because I want to try and pin down these problems I am having.

Here's a list of a few maintenance things I've done so far: cleaned MAF (done at a shop) and cleaned TB, new fuel filter and pump, replaced ICM (original was bad), checked coils (all good), and new spark plugs and wires. Current mods: Intense 3.8" pulley, Intense PCM (yes, canned for right now), ZZP Plog, ported rear exhaust manifold, 3" DP, high-flow cat, and solid motor mount.

First off is this misfire I'm having. Whenever the engine is idling, or below 1,000rpms (such as coasting down a big hill), I have seen misfires on cylinder 4 (and only cylinder 4), between 2-12 (mostly just 2). Now, what I find odd, is this only happens at idle. While cruising or opening up the throttle - nothing - I get nothing but smooth acceleration with 0 misfires. Any ideas on why this happens, or should I not be concerned with it? I've checked the plug and wire, and everything seems good and secure.

Next up is knock. At light to medium heavy acceleration, no KR, but if I really get into, I normally see my KR jump between 0.2* to 3.9* (I did see it hop up to 4.2* one time). So, I stay away from WOT, unless it's really necessary (usually when I'm trying to merge onto the interstate). I don't think it's heat related, as it has been very cool here that last few days, so is there anything I might be overlooking, that might help bring it down more?

Last thing is my mileage. Cruising on the interstate is fine, but in town is where it suffers. Light acceleration between 1300rpms to 2000rpms gets me between 3-8 mpg on the DIC (my Aerforce reports very similar). It never used to be that way. I have noticed a lot of carbon buildup on my exhaust tips recently, and it's making me wonder if I might be running too rich?

Also, here are a few more questions I have:
-- I know I should change my PCV (put on at 98K, now have 141K), but that really shouldn't cause too many issues, should it?
-- When my spark plugs were changed, they were found to be fouled out (I was told there was carbon on them too), so even though it's nowhere near time to change my O2 sensor, could it also have some crud on it (that maybe I can clean off, or if not, just having to replace it) that might be contributing to one or some of the above factors?
-- Is it possible, even though I regularly run cleaner, that my injectors may no longer be flowing properly (or matched), or is that something I shouldn't be concerned with, as that doesn't happen often?
-- If I am running rich, is there anything I can test for that? I have an Aeroforce Interceptor gauge, and according to my math, I'm getting almost 26mpg with a combined 30% town and 70% highway, so I'm not rapidly going through fuel.

My worst fear is that I may have something internally wrong with this engine (it was very abused and neglected by it's previous owner).

Sorry for the long post, but I just want to try and nail down some of these problems, and with this being my DD (the Buick is currently out of action), I worry things may get worse if I don't get a handle on these problems.

Thanks again in advance for any help you guys can give me!

[gweg_b]

Sorry to bump, but any ideas? If I have to get parts, I'd like to try and order them soon (possibly before next week).

[Archon]

Start by checking to be sure that the #4 plug wire is not touching or very close to the wiring for the O2 sensor. What plugs are you running? I don't know if the aeroforce reads fuel trims, but if it does, what are those? Checked for vacuum leaks?

[gweg_b]

Ok, tonight I'll check and see where the #4 wire is at, and make sure it's not touching the 02 sensor. The spark plugs are NGK TR55 Iridium. I don't know if the Aeroforce can see fuel trims or not, I'll have to look. I haven't checked for any vacuum leaks yet - my brother did that last year I think, but I'll check.

What is the best way to check for leaks? I remember reading somewhere that you can use carb cleaner. Do you just spray it on the hose? Would throttle body cleaner work as well, if that's the method (don't have any carb cleaner at the moment)?

[Archon]

Carb or throttle body cleaner will work fine. Spray along hoses, vacuum Ts, and the intake. Pay close attention to the T under the supercharger which has a tendency to get brittle and crack. The capped off vacuum connector on the top of the supercharger can also leak.

Does your KR coincide with shift points?

[gweg_b]

Number 4 wire is clear of the O2 sensor. I'll try and check for leaks later this weekend, at a wedding right now.

The KR happens throughout the powerband, but mostly anything above 3K. Shifting doesn't seem to matter, so I don't think it's false KR from the tranny. I'll try and take it out for a few hard runs here soon, and see how it responds while it shifts.

[nickburgundy]

aeroforce does read fuel trims. You want to look at the long term trim @ idle 20% 50% and wot%. basically more in 2nd gear. That will give a good indication to vacuum leaks. Also this may sound dumb but I had my fwi filter fall off once and got lots of kr.

[gweg_b]

Update 11/3/12:

So, as mentioned in another post, I had some leaks and electrical issues that made me have to park the car for awhile. I recently got it back on the road (still missing most of the interior at the moment), and noticed some changes since the last time that I posted in this thread.

Misfire - Really don't know the situation at the moment (haven't checked, as I've been monitoring other issues), if that #4 is still missing, but I'm not really concerned as that wasn't causing any issues (refresher: it was occasionally getting about 2 misfires per cycle at idle).

Mileage - That has gone down. Before the tear down, I was getting almost 26 mpg, now, it's slightly less than 24 (the car is even lighter). This might be attributed to the colder air and winter gas mix.

Knock and Fuel Trim - This is what I'm concerned with. Before, I saw the max KR of 4.2*. Now that the car's back on the road, I've seen up to 8.9* of KR. I've also noticed that I am running more towards Lean conditions now. At light throttle (20-30%), I've seen my short term fuel trims hit as high as +11.5% (it normally hangs between +3.9 & +7.2). At cruise it usually bounces between -2.9 to +3.2. WOT my trims are slammed at 0. That leads me to believe I might have a vacuum leak. However, all the fittings, connectors, and hoses test fine (I ran out of throttle cleaner before I could test the intake).

My questions are:
1. If the vacuum leak(s) is not at the mentioned areas above (assuming once I test the intake that I find no leaks), where else could one be? If it's not a leak, what else might it be - O2 sensor, injectors, any other sensors not working correctly (and not throwing a code)?

2. I know it's not too far out or range, but last time I checked, my long term fuel trim was around +2.9. Short term seems to always lean more to Lean (as mentioned it has gotten into double digits). I'm concerned, but am I worrying too much? And if the engine is running Lean, but the trims are 0 at WOT, would that still cause the high KR? (Note: the KR does not correspond to shifting, just engine speed.)

When the throttle is opened up, it does not feel like I am losing power - it still pulls very strong. However, I don't want to push it, because last thing I need is a melted piston - as this is my daily driver.

Thanks again, guys, any help is appreciated!!

[JEzze]

im having same issue, im interested to see/help with this . i was told from one of our big vendors some of the ssei are kr prown. also was told that a clogged fuel filter can do this .

[xrob]

Bump

[gweg_b]

I actually did have a small vacuum leak (a "U" shaped hose coming from the TB), took care of it, and that helped fix my trims some. I also got an explanation on the trims from my brother that kind of cleared up my misunderstandings about fuel trims.

Anyway, I'm not running nearly as lean now, but that dang knock is still there. I need to check the O2 sensor (since the old plugs were a little black), but I doubt, at this point, it's the sensor. With my limited knowledge of engines, I have exhausted my resources. I'll have to smoke test the engine at some point.

i was told from one of our big vendors some of the ssei are kr prown. also was told that a clogged fuel filter can do this .

This fuel filter has maybe 6-7k on it. I might change it soon, but I'm doubtful that's my issue. But as mentioned, if my engine is prone to knock, I might just have to live with it and hope for the best.

[Alybue2]

I have the same issue. I have a 2000 Bonneville SLE with 204,000 miles. I have long starts where it sounds like it is trying to flood itself, cylinder 5 missfire at idle or under 1000 rpms, no loss of power under throttle or deacceleration. I have done new plugs(acdelco), wires(acdelco), coil (acdelco, one tested bad), oil pressure sensor(acdelco, sensor was at zero hit a bump and oil pressure would go to max). The previous owner said they changed the fuel pump and fuel filter 6 months before I bought it. I have been searching this forum and have not found any concrete answers. I do not want to throw parts at it and would prefer to fix the problem. It has been in the single digits lately and seems to become harder to start. There are times that I have to crank for so long that the battery almost dies. At one point I had to jump it because I killed the battery trying to start it. I have ideas of what it could be, but I would like advice on what to test.
Thank you in advance

[01bonneSC]

I have the same issue. I have a 2000 Bonneville SLE with 204,000 miles. I have long starts where it sounds like it is trying to flood itself, cylinder 5 missfire at idle or under 1000 rpms, no loss of power under throttle or deacceleration. I have done new plugs(acdelco), wires(acdelco), coil (acdelco, one tested bad), oil pressure sensor(acdelco, sensor was at zero hit a bump and oil pressure would go to max). The previous owner said they changed the fuel pump and fuel filter 6 months before I bought it. I have been searching this forum and have not found any concrete answers. I do not want to throw parts at it and would prefer to fix the problem. It has been in the single digits lately and seems to become harder to start. There are times that I have to crank for so long that the battery almost dies. At one point I had to jump it because I killed the battery trying to start it. I have ideas of what it could be, but I would like advice on what to test.
Thank you in advance

Best bet is to start your own thread. That way we aren't trying to fix 2 problems in one thread. It will keep the flow of information from getting criss crossed