vpshockwave

I made a similar topic awhile back that was more related to tuning but I believe my issue is not a tuning issue anymore. I think it may be some sort of vacuum leak or other physical issue (not computer related). A lot of things have happened over the past month or two so I'm going to condense it into a chronological list for ease of reading:

1. Car had a cam/exhaust/intake done over a year ago (G5X3, LG Super Pro Long Tube Headers, K&N Intake). Tuned and had no issues.
2. Car is taken in a month or two ago for AFR 210 heads, FAST 102 intake manifold, electric water pump, centerforce clutch, LS2 fuel rails, 90mm throttlebody, and 42 lb injectors. Tuned and seems fine.
3. Immediately upon picking up the car I notice the idle is extremely erratic when rolling to a stop (bogs down to 200-300 rpms, revs back up to 2000 rpms -- keeps doing this back and forth, sometimes dying, until I come to a stop). Upon stopping the idle goes back to normal. AC on or off makes no difference. Car seems to drive fine though.
4. Car is returned and retuned but erratic idle persists.
5. Took the car on a road trip to California with the intention of returning the car again when I got back to address the idle issue. Notice knocking about 3/4 of the way through the trip when car is under heavy load in 6th gear (cruising up a hill usually). I was in northern Arizona and it was extremely hot so at the time I thought heat was a contributing factor.
6. Limp the car in lower gears the rest of the way and have the car retuned from scratch by a reputable tuner in California to address knocking and idle. Seems to be doing fine, idle seems much more stable and knocking is not present. Tuner mentions he did not have time to check for vacuum leaks because I was under time constraints to get the car back.
7. Begin return trip home to Texas. Seems fine initially, starts knocking in 6th again under high load at some point. Also notice that the erratic idle seems to be present at the same time the engine is knocking (not at the exact same time, just in general, the two issues seem to coincide).
8. For the middle leg of the trip both issues seem to disappear. No knocking under WOT in 6th, idle is smooth as butter.
9. Wake up to finish last leg of the trip. Engine is knocking in 6th again and I can't even roll the car to a stop without the engine dying. I'm having to give it gas while coming to a stop to keep the engine going.
10. Finish the last leg of the return trip in 5th to prevent knocking.

I'd like to point out that lower octane gas was used later in my trip, but even after putting 5 gallons of 100 octane competition fuel in the knocking was the same. When it was retuned it was tuned to 91 octane gas, and the same gas was present when it was running fine and when it was knocking so this should not be octane related knocking.

Does anyone have any ideas as to what the issue could be? Could a vacuum leak or for that matter any other type of leak cause knocking and a bad rolling idle? I'm open for any suggestions. I plan on dropping the car off at the guys that did the original work to see if they can sort it out but I'm trying to get a list of problems it could be together.

Thanks

vpshockwave

Hey guys,

Can someone tell me if this is normal or not? I was under the impression the intake manifold should essentially be completely dry. I even have a catch can that's supposed to help with that. This intake manifold only has ~3,000 miles on it.

TNBUSA

That is not normal...time for a leak down and compresson test. My wifes Z06 has the G5X3 and we had time getting it to idle without dying. It also doesnt like to be lugged in any gear. I think the knocking was detonation which probably took out a piston

vpshockwave

Thanks TNBUSA.

I took out the throttlebody and intake manifold and cleaned both. The throttlebody had a very light coat of oil and the manifold was terrible (as you can see in previous picture). No particular intake on the heads seemed worse than the others so I wiped everything down and put it all back together. I noticed something on the back of the FAST 102 though and I'd like advice. My MAP sensor is on the back as well as a vacuum line, but there is also a much smaller nipple that leads into the intake that I did not find any line attached to. It appeared completely open to the outside world (albeit the nipple is extremely small). Is it possible I yanked something off of it without noticing? Or should I plug it up?

When I was cleaning the intake manifold I also found a lot of dust/debris in the fluid. See the second to last picture.

When I put everything back together I can hear a hissing from the back which brings me back to that nipple. But I also realized afterwards I forgot to put the clamp back on the vacuum hose so I'm going to have to pull it again (double check your work people). I have attached a picture of the nipple in question (giggity) if someone has some insight into what it is.

I'd also like to point out that to my knowledge the PCV valve has been deleted.

Thanks!

neutron82

there is a small vacuum line at the back of the intake for the ac controls... if these tuners are tuning your car without finding and fixing any mechanical issues first then I would look elsewhere, the tune will only be as good as the cars mechanical condition

vpshockwave

Thanks. At this point I'm just trying to find things that need fixing. I noticed that my catch can was installed backwards by the same guys which explains all of the oil in the intake. Once I get all of these hoses situation and make sure everything is routed correctly I'll figure out where to go from there.

racebum

need to do a compression and cylinder leakdown test. if that looks good you can continue, if it's not you're wasting time trying to address anything else

vpshockwave

That's next on my list, though at this point I'm just going to give it back to the original guys and let them figure it out -- the issue didn't started until the most recent upgrades and tune so it's most likely related to something they did.

I removed the intake manifold today and reattached the HVAC tube (the one I was asking about). I also added about a 1 foot extension to it to make it easier to deal with in the future. I also relocated the MAP sensor to the front while I was at it by splicing in my own wires and tubing it around. Plugged the previous rear location as well. Fixed my catch can flow to be correct. Car was acting really weird, let it relearn idle and it's still weird but it's the same weird I've had so the issue lies somewhere else obviously.

I don't have a picture, but I did notice some scarring around one of the intake ports on the driver's side heads. Close to where the intake would seal it looked like someone had scarred it up real bad with a screwdriver. I'm not sure if it's bad enough to cause my issues, but if it wasn't quite sealing right would it cause similar issues?

neutron82

spray some carb cleaner around the intake where it meets the head near the area in question... if there is a leak it will suck in the carb cleaner and you should hear a difference in the way the motor runs

vpshockwave

I may try this. I sprayed all around the edge of the intake but I didn't realize the area where it seals is fairly open so I may give it another go and spray between the manifold and heads. Will update with results, if any.

racebum

if they put too much timing on the map you may have already blown a hole in a ringland via detonation. that causes the exact symptoms you describe

only one way to know for sure...test

vpshockwave

I get it, but that costs money, so I'm doing everything I can BEFORE I spend money. I've got nothing but time here.

neutron82

have you checked the parts stores to see if they rent out compression testers?

vpshockwave

I checked around online and it's possible my local autozone or oreillys has one, but I won't know until the morning. There are more stores in Tyler but that's a solid 40 min drive on way so I'm avoiding that as much as possible.

vpshockwave

OK, went ahead and rented a compression test kit for the hell of it. I didn't warm up the engine much because I would've burned the hell out of my hands trying to get the spark plugs out, but each chamber held 165-175 psi successfully.

racebum

a compression tester is $15-30 dollars, a leakdown is around 100 but compression should be enough to let you know if there is a hole in the engine

i'm sorry but i have to LOL a little. you mod cars yet refer to $15 as spending money?

modding cars while tight on money is just such a facepalm

if all 8 holes show similar compression that at least tells you the long block is healthy and you can start tracing things down elsewhere.

vpshockwave

Took pictures of my spark plugs as well to get everyone's opinion on their condition.
#2 & #4


#6 & #8


#1 & #3


#5 & #7

vpshockwave

I'm not tight on money, I just don't spend money needlessly. Please facepalm your way out of my thread.

vpshockwave

I finally got a picture of this. I'm going to put a light coat of RTV over the scarred area to make sure it's sealing correctly, as well as RTV in and around the intake seals on the manifold itself.

vpshockwave

OK, I added some RTV to the manifold and a little around the scarred area just in case to help with sealing. I put everything back together and did the relearn idle procedure. I made a video showing what it is doing. It's almost like it's the complete opposite now -- rather than bogging down and dying it's revving way too much on its own while rolling in neutral. See what you think. The times when I'm coasting are @ 6 seconds and @ 41 seconds (direct links below). I'm partially thinking that perhaps I've fixed the issue, but my current tune was built around the issue so it just needs to be retuned: