verbs

I don't know why my car is doing this, but upon cold startup the car stutters really bad at low rpms (up to roughly 2500rpms-3000rpms or so) upon acceleration. The engine is shaking pretty badly, and if feels like I'm only running on say 5 or 6 cylinders. The car accelerates as if it only had about 150-200hp. During acceleration, all of a sudden without warning, the engine just goes back to normal at around 2500-3000rpms and pulls great.


The shop that installed my LSX intake as well as a buddy of mine both checked for vaccuum leaks around the manifold and found nothing.

I'm stumped and can't figure out what might be causing this. My brakes seem really mushy as of late too, and of course, I'm down about 40rwtq down low and about 30rwhp/30rwtq down from where I should be all around.

Any suggestions? I've swapped MAF sensors to no avail, and changed the valvetrain around. I'm going to test if the weatherpack plug on the MAF sensor tomorrow, but other than that I'm stumped. Any ideas?

Damian

iTrader: (89)

Sounds like normal cold start up surging to me. My cam does that a little bit when cold, kinda stutters below 3K until it's warm and then goes away. Your cam is a LOT bigger than mine, so it'll probably be a bit worse...

SouthFL.02.SS

Mine does the same stuttering for the first 3,4 minutes, then runs fine. I need to retune at some point.

verbs

This definately does not feel like surging. I've had cold start up surging with both the G5X3 and TR230/224 ,and this cam surges no more than my old cam does, and the surging never affected driveability above say 1200rpms or so with the old cam, so I don't see why it would with this cam.

The car will idle fine after about a nice 20 second warm up.....what I'm referring to almost feels like a mini earthquake in my engine about 1-2 minutes after startup after the initial cold start surging takes place.

Damian

iTrader: (89)

Gotcha. Could have a problem somewhere. That kinda stuff is hard to diagnose over the internet

Dude all things considered, the G5X3 is almost twice the size of your old cam. I wouldn't be suprised in some major surging @ cold startup...

verbs

I'm sure my aluminum flywheel doesn't help. Surprisingly, the idle isn't really much worse, if even worse at all than the TR230/224 on the 110.8LSA.

I'm hoping someone else has seen this same issue before and found a fix.

frcefed98

iTrader: (16)

kinda feel like the gas gets pinched off then, all of a sudden the gas turns on again and the car accelerates normally? Mine does this too, The engine is new and so is the big cam. I'm thinking vacuum leak around the intake manifold. My car falls flat on its face when I try to accelerate, then past 3500 it wakes up and goes??????
I just don't want to spend 50 bucks on stock LS1 intake manifold gaskets again
I will be ripping into it tomorrow, maybe my knock sensor harness got under the intake manifold funny and it lifted one side????
Let me know if you find out what it is.

verbs

Yep, sounds exactly like what is happening to my car. Hopefully I can find out what's going on. Heads and intake are coming off in the next few weeks myself.

Scalpel

iTrader: (4)

May be your 02 sensors. My brother's car did the exact same thing, usually when it was wet, as soon as he'd hit a certain RPM it'd be fine. Also, it would completely go away after about 2 minutes regardless.

verbs

When I logged my o2 sensor activityduring dyno runs I noticed they weren't switching as fast as they should be. It's probably time to replace them and that could very well be it.

Scalpel

iTrader: (4)

If you can, try to log your car on start up to catch this scenario happening and see if the O2s are working properly.

98Aggie

iTrader: (19)

I am currently having the same problem on cold start ups. So far I have installed new plugs which where fouled but did not solve the problem. With Auto Tap I am seeing a high number of misfires on Bank 2. I started to monitor my O2 sensor. When cold it reads 1150mV, after start up about 20 seconds later when the engine gets to about 120F, the O2 sensor starts to responed an then I get the misfires. I beileve when the car is cold the sensors should reas 200 mV or less. I am going to get a new O2 sensor and see if this fixes the problem.

kossuth

iTrader: (12)

First question here is who installed the camshaft in the motor? I'm just wondering if maybe the cam retainer isn't in there right and maybe it is walking. And the harmonics of the motor at the upper RPM's is what is keeping it back where it is supposed to. Just a wild idea. Violent misfires and shaking just make me think that something is off somewhere. If you installed it then you know the likelyhood of this happening. If someone else did then your guess is as good as mine. Also did you check the grounds on the heads and such? Perhaps there is a bad ground with one of the heads or even the block and it is doing this. If you don't have a ground strap on the heads I would get a braided cable and find a good spot to ground it and see if that fixes anything. You may have already done this though. It might also be a good idea to use some dielectric grease on the ends of the cables to help with the electrical connection being aluminum isn't the best conductor in the world. Another idea is do you possibly have a vacuum leak around the fuel injectors? Maybe you don't have the injectors seated 100% correctly. They should have used Vasoline or something like that on the O ring on the injector when it was installed. I can't think or anything else at this moment unfortunately. I hope you get it figured out man, and hopefully it is something simple.

Just thought what about the flywheel and clutch assembly? Has that been messed with?

Cheatin' Chad

iTrader: (3)

I assume this is only under load?

I had a similar symptoms not too long ago.

I changed my plugs.Of which four turned out to be heavily fouled I had to clean the soot off of one of my o2 sensors.

Is there any chance you have a loose/damaged plug wire or did have for awhile?

If the problem is not only limited to when you have a load on the engine

Check and double check for vacuum leaks. Spray carb cleaner,starting fluid,wd40,etc. (whichever YOU feel comfortable with-No suing me if the ether blows up on you ) around areas you suspect leaks. Idle will generally increase if any of these chemicals are drawn into the intake via vacuum leak. If you're extra paranoid or have painted parts underhood you can use water and wait for the idle to fall off. Water is nowhere near as quick as the others though.

You can use a spray bottle to mist water on your exhaust headers/manifolds to check for a non firing cylinder(due to lack of fuel or spark). Spray all of the exhaust tubing on one side of the motor if one takes much longer to boil off the water that cylinder is not up to temp. Check the plug,wire,coil,injector,etc. there.

Use a screwdriver or a mechanics stethoscope to verify proper function of your injectors. Listen to each individually and see if any one or two sound different from the rest.Obviously you'll hear a rapid ticking from all of them. One pulsing significantly slower would signal some kind of problem.

Good luck! Hope you get the problem wrapped up soon.

verbs

I had 2 bad plug wires recently that were bad for about a week. I do know my o2 sensors could use changing.

99 Black Bird T/A

iTrader: (4)

How much long do you let the car warm up before putting in gear and driving?

Could a faulty cam position sensor cause any of the erratice behavior?

verbs

I give it about 20-30 seconds or so....but the erradic behavior occurs for the first couple minutes of driving after that. I'm clueless as to the faulty cam position sensor, but I'm assuming I'd pull an SES code for that, yes?

gojo

iTrader: (12)

Try increasing yout RAF values at the temps affected.
Has all this happened since the intake install?

verbs

all this just started happening since the intake/cam install.

gojo

iTrader: (12)

The 90mm Fast needed a lot of tuning in the Idle and limiters tables, on mine.
When I tuned mine, I had to reduce the IAC and RAF's by about 4. I did that across the board until I got rid of racing startups. I had to go back and raise the RAF's across the board and then a little more in the cold temps to smooth out running until the engine warmed.