The Tale of the Stumbling Vette

[Vettezuki]

Well I've had this issue of the Vette not gettming more than half a mile or so before it would go into horrific lurches/stumbling. It's a Paul's (ls1z28's) house now and he's trying to figure out WTF is wrong. And it's a mystery so far.

Every electrical connection and relay has been checked. The harness has been inspected for any frayed wires. The alternator has been checked, the battery. the computer has been checked, including disassembly to check for cracked soldering. Nothing is wrong. We're down to two ideas, and if that doesn't solve it the one remaining is a real bitch assuming we haven't forgotten anything else.

So tomorrow, he'll be replacing the cam position sensor. It isn't throwing ANY codes, but it is possible to fail intermittently without throwing a code apparently. After that, we'll reflash the computer. The negative battery cable wasn't really well connected and showed signs of arching, *maybe* it corrupted some part of the flash with a surge; but that's a fairly wild hypothesis. So what are we left with then? Crank shaft end play, which can cause this kind of behavior. But that means removing the engine, etc. Not something I have money for now. So hopefully it's the cam position sensor.

The only thing we can say now is that it doesn't appear to be anything in the electrical system itself and seems to only happen when the computer goes into closed loop. If you fire it up and drive it immediately, it's ok for a minute or two.

On the upside, we discovered the MAF was dying, replaced that and now all the misses are gone. He's replaced the ignition switch, which was fried and was probably related to the poor starting situation. We're replacing the negative cable (already replaced the positive) just to make sure there's good current, useful thing to do anyway.

[Shaolin Crane]

I really doubt it's a camshaft issue, have you checked all things related to the fuel system?

[Vettezuki]

I really doubt it's a camshaft issue, have you checked all things related to the fuel system?

Pump and relays, yes. The filter regulator may be a little clogged, but that wouldn't explain this behavior.

[kdracer73]

Does he have a scan tool that can do data logging? We need to see what data is changing/dropping out. How close is is the current location to Fullerton. I can bring a good scan tool Sat evening .

[Vettezuki]

Does he have a scan tool that can do data logging? We need to see what data is changing/dropping out. How close is is the current location to Fullerton. I can bring a good scan tool Sat evening .

He has the Tech II. :huh: Will that do it?

[Shaolin Crane]

Yes

[kdracer73]

He has the Tech II. :huh: Will that do it? Yes ! Probably better than mine. Tech II is the GM factory tool.

[blackax]

He has the Tech II. :huh: Will that do it?

A Tech II is the best tool for the job...

What is the fuel pressure?

[Vettezuki]

A Tech II is the best tool for the job...

What is the fuel pressure?

Around 58 and stable.

[Vettezuki]

Just got a text. Still driving him nuts. This is some crazy ass gremlin. :mad:

[Shaolin Crane]

Seems like typical GM wiring :huh: :smack:

[94cobra69ss396]

It's not just a GM thing. I've had an issue with the Cobra lately where at full throttle and high rpm the engine cuts back to idle. It was just happening occasionally had then it got to where everytime I go full throttle between 5400-5800 rpms it will cut out. Yesterday after driving it to the store the idle decided to just to 2200 rpms. There are no vacuum leaks and the the IAC isn't stuck open. This is why I like a carb!

[Shaolin Crane]

It was a joke, i actually had you in mind when i posted.

[94cobra69ss396]

i actually had you in mind when i posted.

Don't say that, Ben will get jealous.:rolling:

[Vettezuki]

This thread is about me and my needs!

[Shaolin Crane]

This thread is about me and my needs!

http://www.ruggli.com/bilder/inhalt/produkte/cl-3m_tampon.jpg

:leaving:

[Vettezuki]

Nice Guy . .

Paul has the Tech II, but he says he needs the event recorder to record real time data while driving.

kdracer, does yours do that as it is?

[Shaolin Crane]

I thought you had that bluetooth data logger app?

[blackax]

I thought you had that bluetooth data logger app?

Those ODBII apps suck for real time data logging

[kdracer73]

I believe it does.

[Shaolin Crane]

The data logger on my SCT works great, unfortunately, only for Ford :(

[Vettezuki]

Those ODBII apps suck for real time data logging

Mine with Torque has worked in the past just fine. It's an avenue we may explore this weekend if he doesn't find the problem by then. . . . At this point, it looks like some weird combination of factors that's very hard to tease out.

[Vettezuki]

One 02 Sensor was acting wonky and a the coolant sensor finally threw a code. Replaced the 02 sensor and it drives better overall, but still has the primary issue. Going to replace coolant sensor. . . fingers crossed. Paul has been at it all week and he's about to set the damn thing on fire.

[Vettezuki]

Looks like it's fixed!

The primary culprit looks like a coolant sensor that was intermittently failing but not throwing a code. A lot of other things were improved along the way, the MAF was bugging out, and causing misses, an O2 sensor was a bit chaotic. Should run about as good as it ever did when I get it back. Hope that was it. Looking forward to a little romp time. :thumbs_up:

[Shaolin Crane]

Coolant sensors can definitely do wonky things, its a common issue on foxes

[Vettezuki]

Well, it's much better but not fixed. This is some kind of elusive bastard problem. Before I couldn't drive it hardly at all. THis time I went to pick it up and made it several miles, planning to take Ortega back (brilliant! I know). At the base I setup my logger, and nailed it and it did it, but just very briefly, then seemed to be sorta ok climbing the hill, for a while, then shit itself more or less. So then I turned around and it was basically fine.

It seems to be wors when accelerating from a slow speed (even moderate acceleration when turning), and if climbing for a long while. It's basically fine on the freeway, even accelerating. What a piss off. I'm really wondering fuel system something, but pressure didn't really drop when measuring before. The tank is a bit dirty and the filter/reg is over 10k miles and more than 4 years old, everything with long periods of sitting.

On the upside, when it was running fine, it seemed to be as powerful as ever, that's probably mostly the MAF if figure and the fact there are no more misses. I logged a bunch of data. I'll upload later.

[kdracer73]

The shop next door borrowed the scan tool today and I forgot to grab it.

[Vettezuki]

See attached. Should work with Google Docs or Open Office (I think) if you don't have a current Excel.

[Shaolin Crane]

How's the TPS voltage?

[jedhead]

Is the fuel fresh? I had a tank of bad gas that cause my car to behave in a similar way. I had to burn through the tank, add gas treatment and burn through a second tank with gas treatment then the car ran fine.

Bob

[kdracer73]

See attached. Should work with Google Docs or Open Office (I think) if you don't have a current Excel.
I can open it. will see if I can find any thing..
My scan too will graph info, which makes comparing easier.

[blackax]

It looks like your fuel trim drop to zero on both sides every now and then. That could very well be the issue. Where did you measure the fuel pressure at the rail or at the filter?
It could be the fuel regulator?

[Vettezuki]

It looks like your fuel trim drop to zero on both sides every now and then. That could very well be the issue. Where did you measure the fuel pressure at the rail or at the filter?
It could be the fuel regulator?

At the rail.

Isn't fuel trim just an offset? IOW, when it's at zero it's no altering the default programmed values or something like that?

[Vettezuki]

Is the fuel fresh? I had a tank of bad gas that cause my car to behave in a similar way. I had to burn through the tank, add gas treatment and burn through a second tank with gas treatment then the car ran fine.

Bob

I do wonder if that's part of the problem. It definitely had some gas in there that was sitting for a long time.And it does *maybe* seem to be getting better with driving.

[kdracer73]

It looks like your fuel trim drop to zero on both sides every now and then. That could very well be the issue. Where did you measure the fuel pressure at the rail or at the filter?
It could be the fuel regulator?


Fuel trim is offset. 0 trim is neutral + or - is adding or taking away from the base 0.

[Shaolin Crane]

Best bet is drive the car till the tank is near empty then fill with a few gallons of race fuel. Then regular, should clear out the old fuel

[Damian]

Can you log engine knock?? Your fuel trims are all over the place and your timing has huge dips here and there. I agree with the bad gas theory.

[Vettezuki]

Best bet is drive the car till the tank is near empty then fill with a few gallons of race fuel. Then regular, should clear out the old fuel

What does race fuel bring to the party? I actually have a 76 station less than a mile away that has 100, but I'm not sure they turn it fast enough to be fresh.

[Vettezuki]

On the upside it seems to have its original power back when not falling to pieces . . . I'm guess this is probably mostly the MAF. I do get a lot of spark knock on 91, but with fairly advanced timing (40 degrees) and stock manifolds and cats with crazy back pressure (3psi) on my slightly more than 11:1 comp heads, that's to be expected. This is a separate issue, but I don't want to decompress the heads with gasket or anything if I don't have to. I'm hoping some open headers/exhaust and full retune will make it work with 91.

[Damian]

Maybe pick up some headers or at least pull back the timing a bit, maybe +35?

[Vettezuki]

It's definitely getting better with driving, except for the age old warm start idle hunting issue.

But then at an intersection last night, my gd clutch pedal rod actually bent . . .That sucks because it's not an off the shelf part, it has to be modified from a truck MC unit.

[blackax]

It's definitely getting better with driving, except for the age old warm start idle hunting issue.

But then at an intersection last night, my gd clutch pedal rod actually bent . . .That sucks because it's not an off the shelf part, it has to be modified from a truck MC unit.

It's all those clutch drops you do from 4000

lol

[Vettezuki]

Got the new clutch pedal rod fabbed. Putting it place was a PITA, but I think it might actually be impossible to get the snap ring back on on the MC side.

kdracer, do you have some snap ring pliers with looonng teeth?

[Vettezuki]

It's been running better, nearly fine. Took it all the way to Temecula today and back through Ortega. Brought it home, washed it. Took it for a tank up. Still fine. Cleaned it a little more, then went to move it and the issue is back 100% as bad as it ever was. I can only think of the following things:

1- I managed to tank up with another shitty tank of gas. This is at a busy chevron so I find it unlikely. It also ran fine for 10 minutes or so after tanking up about 2/3rds.

2- Some water from washing settled in on something and it's shorting something in the electric system. This is possible I suppose, but it would mean the water settled after going to tank up while it was still driving fine.

3- The fuel pump has just been intermittent and now it's going out hard.

[Damian]

Fuel pump or the fuel pump wiring?

[Vettezuki]

Could be the wiring . . . How would I really isolate that?

[Shaolin Crane]

Replace it.

[Vettezuki]

I'm leaning towards some wiring thing related to moisture. I took it out just a touch tonight (24 hours later) and it was way better, until I turned at the end of my culdasac and it went nuts. Something in the turn appeared to make it go weird, yet coming from ls1z28's house it was fine. The only things different were washing the car and tanking up. :huh:

[Damian]

Rewire it with thicker wire and see what happens. It will help even if you have to replace the fuel pump.

[Ryridesmotox]

Dude, I have HP tuners, I can datalog it as long as the OBD2 port is within reach of my laptop and the cable. I live in Wildomar, if you head over to Temecula again soon let me know and I can graph that mofo and wee can see whats up. Just one thing, I need to know what engine/mods you are running in that thing so I can make sure I have the appropriate config file.

I'll be able to see anything that the ECU will monitor, hopefully we can narrow it down.

Oh, one more thing, if you can find an ethanol station near you, that would be an even better alternative to the race fuel. The Ethanol has very high detergent properties, and its muuuuch cheaper than race gas, if you are looking to clean the fuel system a bit, dump like 5 gallons in a 20 gallon take and it shouldn't effect performance. you will be running like a E20 blend depending on what is at the pumps

[Vettezuki]

Good to know! There is a brand new station with E85 at the pump near by. I don't think I could make it out of my neighborhood right now. I really think it's something wiring/mositure related, but who knows for sure. . .

[Shaolin Crane]

Dude, I have HP tuners, I can datalog it as long as the OBD2 port is within reach of my laptop and the cable. I live in Wildomar, if you head over to Temecula again soon let me know and I can graph that mofo and wee can see whats up. Just one thing, I need to know what engine/mods you are running in that thing so I can make sure I have the appropriate config file.

I'll be able to see anything that the ECU will monitor, hopefully we can narrow it down.

Oh, one more thing, if you can find an ethanol station near you, that would be an even better alternative to the race fuel. The Ethanol has very high detergent properties, and its muuuuch cheaper than race gas, if you are looking to clean the fuel system a bit, dump like 5 gallons in a 20 gallon take and it shouldn't effect performance. you will be running like a E20 blend depending on what is at the pumps

Uhm you have that backwards, you dont want detergent in your fuel and you want to run something lime race fuel or avgas in it since it has no additives. Its also super corrosive to everything it touches. Personal opinions aside, i dont think it will help. Yes its expensive stuff, but right now i'm sure Ben wants his car back.

[Ryridesmotox]

Uhm you have that backwards, you dont want detergent in your fuel and you want to run something lime race fuel or avgas in it since it has no additives. Its also super corrosive to everything it touches. Personal opinions aside, i dont think it will help. Yes its expensive stuff, but right now i'm sure Ben wants his car back.

True, I kinda got the idea that the gas was dirty from the other posts, I didn't realize that they were all like 3 months old, Ethanol wont help at all in that case.

[Damian]

Honestly, your problem sounds a lot like a buddy of mine had. He thought it was a bad fuel pump. He pulled it out and found the wiring in the tam was all shorted out. Rewire the whole thing and maybe even change out the pump while you are in there. Go buy some cheap 8 gauge wire and redo it all. You can probably get the wiring for like $40.

[Vettezuki]

Here's the problem. I know next to nothing about wiring. Let's start with this.

Que es "tam"?

[Damian]

I hate autocorrect on this phone sometimes. It's supposed to be "tank" not tam.

[Boosten ya]

This sucks man. Hope you get it figured out soon.