Newly Cammed LT1 Runs Poorly In Closed Loop

[1994lt1]

Recently I installed my CC503 cam with all the supporting mods, (Ultra Pro Mag rockers, hardend pushrods, Comp 918 springs, etc). For now I have a tune from MadZ28. Initially the car started right up and idled perfectly. However on my first drive I noticed that it suddenly took a turn for the worse and started backfiring, and popping and would barely want to move. I brought it back and scanned it while running and noticed an insane amount of knock, which I presumed was being detected from the new rockers and valvetrain noise, which in turn was retarding the timing. So I ordered a LT4 knock module and adjusted the valves correctly.

I put the module in and it started right up again and seemded to run better. I went to go around the block after it warmed up and it started popping and backfiring once again, exactly like it had. I scanned it again and noticed there is a constant 4 degrees of retard at idle and slightly less but still alarminly high knock count (7k now 22k before).

The Opti in the car has maybe 5k miles on it and it 2 years old. The ICM, anc coil are both relatively new as well (last 2 years). It is a night and day difference between open and closed loop tough so I am figuring it has to be some type of sensor that doesnt activate until its in closed loop. I am not sure where to go from here so any help would be appreciated. Thanks guys.

[1994lt1]

Heres a screen shot of me datalogging in before the lt4 knock module http://i623.photobucket.com/albums/tt320/1994lt1/log2.jpg

[sweetbmxrider]

o2 sensors are a likely candidate but the screenshot doesn't really tell you anything.

[grazi]

Isnt AF gallons per second at idle supposed to be around 6-10?

[1994lt1]

I do have a datalog as well. I was thinking o2 sensors as well but I'm not sure

[Pampered-Z]

If it idles fine, and runs "fairly well" under light throttle, and you have the rockers adjusted properly, then I'd bet on you either have plug wires crossed, not clipped into the opti well, or even a burnt wire. Crossed wires is so easy and so common. Check them very closely!

I set the 918's set at 180 install height, and at 1/4 turn past 0 lash.

I'd also suggest you check for a vacuum leak and check the injectors are properly wired - didn't swap connections. Also check the wire to the knock sensor itself. I had a burnt wire that was arcing to the knock sensor and the car had fits as soon as it went into closed loop!

Scan the car while driving and post the file, or send it to me and I'll look at it.

[WildBillyT]

If you email it to me I will post it here.

I take it this car is a 'Vette?

[Anti_Rice_Guy]

If you email it to me I will post it here.

I take it this car is a 'Vette?

It's a 94 Z28

[WildBillyT]

Datamaster is not using the right variables then. Won't effect the scan too much on certain things but it's set for a Y-Body.

[1994lt1]

Yeah I saw that it was for the wrong car. I did check the plug wires and connections and they're all good. It is a night and day difference from open to closed loop though and something like that wouldnt be so different. I'll send the file to your email

[deadtrend1]

I had a similar problem and it seemed to be discovered that i crossed a set of injector wires.

[1994lt1]

I have checked the injector wires and they seem fine. I just did another datalog of the car. I unplugged the temp sensor and the car didnt start so I plugged it back in. I then got code 15 (coolant temp low, expected) and code 16, the code no one ever wants to see.

Heres what I dont understand. 1. I cleared both codes and both went away and didnt come back so was it a hiccup? 2. If this was an Opti problem, why would it only happen in closed loop (literally a night and day difference). 3. Did me unplugging the temp sensor cause the code 16 possibly? 4. If I did have an Opti problem wouldnt the code stay there? I sent the datalogs to WildBillyT so he can put them up here for me because I dont know where to go from here.

[WildBillyT]

http://www.njfboa.org/WBT/log1.uni

http://www.njfboa.org/WBT/log2.uni

[Pampered-Z]

Thanks Bill, I'll try to look at them when I get home tonight.

TEMP sensor should not prevent the car from starting? Is the opti harness in tight? how about the ign module connetions and ground?

[WildBillyT]

You are getting KR even in open loop so something is defiently up.

Is your MAF clean? Does it still have the screen?

[1994lt1]

MAF is clean and stock. I cleaned it when I had it out for the cam swap.

[1994lt1]

Thanks Bill, I'll try to look at them when I get home tonight.

TEMP sensor should not prevent the car from starting? Is the opti harness in tight? how about the ign module connetions and ground?

It started (kinda) but it didnt want to be running thats for sure. When I unplugged it the reading the PCM was getting was -44... Ignition modules and grounds have all been checked when I first experienced the problem. ICM isnt old as well.

[1994lt1]

PamperedZ have you gotten the chance to look at the logs? I'm dying want to drive this car so badly

[Pampered-Z]

PamperedZ have you gotten the chance to look at the logs? I'm dying want to drive this car so badly

Sorry got sent out of state, will try ASAP to get to it.

[Pampered-Z]

PM sent. Initial file doesn't look too bad, but I would like more data if possible.

[Kat]

Thanks Bill, I'll try to look at them when I get home tonight.

TEMP sensor should not prevent the car from starting? Is the opti harness in tight? how about the ign module connetions and ground?

Yeah the car wouldn't start if the the ECM is seeing -44d. It will just dump fuel into the motor trying to start and wont.

[greenformula92]

what program did you guys use to view those logs. I can't get them to open

[WildBillyT]

TTS Datamaster

[greenformula92]

used to have that on my other computer.

[1994lt1]

Well I took it to a shop and unfortunately I don't think he got it. He thought it was because I have a bad plug wire on the p.s. This wouldn't make sense to me because it changes to drastically. I was talked into bringing it home and checking the timing which me ans I have to remove the front cover again...crap. Either that or an opti problem im guessing now.

[sweetbmxrider]

What lifters are on it? Preload? Did you ever do anything with o2's?

[Pampered-Z]

Looking at the one scan, the car seems to run fine in open loop, once it goes into close loop I do seem some very odd O2 splits for 1-2 cells, such as RB at 880 and LB at 53. Which I think could be a miss or maybe an injector sticking. But for the majority of the time the O2s are running close together and the injector pulse and LTs look fine.

I'd like to look at a scan of the car under load and when it starts acting up badly, so I can get a better veiw of the fuel trims, spark advance, knock etc.

[1994lt1]

Lifters are Ls7. I had the guy at the shop adjust the valves again he did 1/2 turn preload.

I'll get another scan of it under load tonight for you. I still dont know how to upload them so maybe ill email it to you?

[1994lt1]

Ok I just logged the car again this time under a load. I sent them to WildBillyT's email so he can post them here for me.

This time out I finally got a code, 33: MAP High which says either bad sensor or vacuum leak to me. I still want to check the timing. When it gets posted tell me what you think! Thanks again guys.

[WildBillyT]

http://www.njfboa.org/WBT/log3.uni

http://www.njfboa.org/WBT/log5.uni

See above :D.

And start looking for a vacuum leak.

[1994lt1]

I do have weak brakes and my fan directory doesn't work, I'm just wondering if this is a result of the engine possibly being out of time. I'm almost positive i didn't set it up right at this point

[LTb1ow]

Did you install it dot to dot? Its reasonably diffucult to really mess up the mechanical timing to the point where it won't run well, but not to the point where you kiss valves.

[1994lt1]

I did dot to dot I'm just not 100% sure the engine was tdc when I did it. It has to be close to run, but I've been doubting myself since someone brought it up to me.

[LTb1ow]

I am not sure if you mentioned it, but is it audibly pinging or knocking? Or are you just going off the knock sensor readings

[1994lt1]

Not all the time, but at times it makes ping noises when it is acting up.

[greenformula92]

If it it a timing issue i don't see how you could screw the opti up, it only goes on one way. now if the cam is a little out of time compaired with the rest of the bottom end than that would cause a problem. but I would think it would cause the problem all the time. The problem is occuring when the ECM starts to use its sensors. so something related to them is probobly what is screwing it up

[Pampered-Z]

you would know if you were off a tooth dot-todot would be pretty obvious.

As greenformula92 stated, the car seems fine in open loop. I'll look at the scans ASAP.

[1994lt1]

When you install the timing chain, the cam dot has to be at 6 o clock and the crank at 12 which will put the cam dowel at 3 right? And all this HAS to be done with the engine at #6 TDC correct? I think I might have been off on the tdc part if anything. I have to check it or it'll always be on my mind.

[Pampered-Z]

If the dot on the crank it at 12 O'clock your at TDC FOR BOTH #1 and #6. Remember that the crank goes two revolutions to complete a cycle, and the cam goes one rev for the cycle. The first revolution is intake/compression (IGNITION) then second revolution is power/Exhaust. If the cam dot is up your on the #1 cylinder ign part of the cycle, if cam dot down you on #6 ign cycle.

BUT, that is only really important on a conventional SBC where the distributor can be installed in various positions, and you want to be on #1 TDC/ignition so that you can get the distributor properly oriented ( Basic timing is pointing the rotor at the #1 spark plug).

Since the opti only goes on one way – as long as the dots match up, your opti will get installed correctly.

[1994lt1]

Oh ok that makes sense now

[greenformula92]

If you can't find any bad sensors then you are going to have to start digging through the harness. could be O2, CTS, MAP, MAF. you don't have any codes right? You have to look at the values of each sensor and see which one is way off. As far as the timing thing goes Im pretty sure thats not your problem.

Also I would comb over for vac leaks just to make sure. But I wouldn't be surprised if you didn't find anything.

Another option is maybe a corrupted tune file? Im just spinning wheels on that. Did you get a base tune to run the cam. I know the ECM is a little forgiving on that but I don't know how forgiving

[1994lt1]

The car acted exactly the same before the tune was installed so I don't think its that. Only code I have is 33 map high

[1994lt1]

Ok so this morning I still have Code 33 while running it. Also I noticed that my IAC is maxed out at 160... I'm thinking now that I do have a serious vacuum leak somewhere. o2's seem to function normally, going from .1xx to .8xx frequently.

I drove it a little to take a video for you guys. In the video I am applying even throttle pressure trying to accelerate and you can see it gets caught up around 1500 to 2000 rpms and makes some weird noises which sound like theyre coming through the intake.
http://www.youtube.com/watch?v=IcFsEaTDGRQ

[greenformula92]

you need to rule out a vac leak. another thing you can try is unplugging the MAP and see if anything changes. in other words if its a faulty MAP sensor throwing everything off you can eliminate it by unplugging it and the car will run. not to its full potential but it will run. if you have a vac leak the problem will still be present, if you don't the problem should be kinda solved, then you replace MAP and you are good to go. Potential vac leaks could be anything from a simple hose or the plenum and lower intake gaskets and so one and so forth. it could be a real can of worms

[1994lt1]

Ok so today I figured I'd take a look at the plug wires the guy said were bad thinking there was just one. There were 3 on the p.s. that were cut into from the belt. These msd wires are too big for their own good. So now I'm looking at wires, problem is that I have otvc wires. Also I looked at my drivers side o2 sensor and it looked rust color, so I'm not sure if i should order 2 sensors or not. I might just to do away with that as a possibility

[LTb1ow]

What kind of headers do you have? !AC or no?

[1994lt1]

I have Pacesetter LT's. !EGR and ! A.I.R. but I still have ac

[1994lt1]

Ok so I just had to order new OTVC wires and 2 o2 sensors. I have to get the ball rolling here this is ridiculous. Ltslow I looked up the length of stock wires and found out that I was nowhere near where I needed to be, longest was like 34 inches or something. Thanks anyway though.

So now I just have to wait for the wires to come in. Question I have is: While I'm waiting should I do anything else? The car is already semi apart so if I were to do something else now would be the ideal time. Also did PamperedZ or anyone else get a chance to look at those datalogs under a load yet?

You guys have been so helpful and great I really do appreciate the help.

[LTb1ow]

Change teh spark plugs and figure out how you plan on routing the wires to avoid them getting caught by the belt this time round.

[1994lt1]

Alright well heres the update, I hope I havent lost people's interest because I need you more than ever!

Replaced the plug wires with new, also did brand new AC o2 sensors and a new throttle body gasket. Car started right up like always and ran at 800 rpm (desired idle). I took it out for a ride and it did seem noticeably better than before, however still has SES light (code 33 low MAP).

Now what is interesting is that the light only comes on during light throttle operation or idle situations. When accelerating or at increased rpm it does go away. This to me says vacuum leak more and more. When the car is "acting up" it bucks and knocks and makes weird noises out the intake. (Weird?)

How do I go about finding a vacuum leak? Where do I look?

[greenformula92]

you could use the cigar test, or pay an hour labor to have a smoke test done, if nothing else you will know if anything is leaking and where its leaking from.

the other thing you can use is a can of throttle body cleaner to spray around the base and plenum, throttle body and where ever else you think needs to be sprayed. lines you may just have to gently feel around

[1994lt1]

I sprayed throttle plate cleaner around the runners and vacuum lines to no prevail. The code comes on now IN GEAR with brake applied. I assume its because the idle drops down so low and it sees low vacuum?

If you brake torque it in gear, the car hesitates, and pops both through the intake and exhaust. Like I said it does this when warm after warmed up. Could this be another OPTI issue?

I unplugged the MAP sensor and it seemed to run better at first but then had the same symptoms.

[greenformula92]

Try taking the MAP off and checking that little rubber donut that the nipple mounts too. Is this on a factory tune or has a tune been applied yet?

[1994lt1]

The nipple was there. It's a little scrunched up. Maybe ill try taking it out and plugging the hole and seeing if that helps. It is in tact though.

The tune has been changed. Email tune from madz28

[sweetbmxrider]

Eek, haven't run into a good experience with a tune from madz28 yet. Not saying it is your problem, just saying there isn't a good track record there.

[1994lt1]

Well I would be worried but it ran like this before the tune as well.

[1994lt1]

Well guys its fixed and it runs like an animal. Timing was off by one tooth...not sure how I did that. I'm just glad its right now! Thank you everyone for your help and patients.

[greenformula92]

wow and we ruled that out. how did you come about figuring that out?

[sweetbmxrider]

Yeah, I thought you also said it was doing this before the cam swap as well?

Oh well, at least its motoring now!

[1994lt1]

Noo it was doing this before the tune, not the cam. But anyway I had a good mechanic friend listen to it and he said it sounds like timing, so apart it came.

[LTb1ow]

Pretty cool stuff man, when you headed to the track with it? :)

[1994lt1]

As soon as I can. Maybe next Friday

[sweetbmxrider]

Good stuff, it definitely helps in diagnosing when you can see and hear what you are working on 8-)

[1994lt1]

Haha yeah I know. I was just asking on here for some sort of direction and it worked. Thanks again guys

[sweetbmxrider]

No definitely, I do the same. Its just tough/frustrating when you can't see or hear the car in question. Keeps you sharp at the same time though, having to consider all variables that are second nature when you are there in person.

Go race it!!!