Bad coil packs?

 

I don't know. Jeff's crew at CAM should find it quick if any are bad. I am simply stumped here. Maybe it's the throttle position indicator causing the car to think the throttle is open or something. Without a computer to hook the thing up to and diagnose the PCM, BCM, and other components I'm toast. I took the car over to CAM yesterday. Hopefully, they can figure it out, I heard that he is one of the best.

 

You mentioned you checked the grounds in the engine compartment. There's one under the car, on the drivers side, at the back of the block. That ground was left loose by a tuner and after a few hundred miles my car did what you describe your car is doing.

 

Thanks a bunch gojo, I'll check this on this afternoon.

 

[QUOTE=walker07;1561178274]I have an Innovate Motorsports, LM1 unt and have used it on my big block chevy, I just haven't gotten the chance to put the bungs into the exhaust on this car yet.

Scott, since you don't have CATs, you can use the clamp on adaptor at one of the exhaust pipes, just for doing a tune. Innovate sells the adaptor but safety wire it on or?? as they come loose easily.

As for the burnt O2 wiring harness, the motor starts in "open loop" so the two O2 sensors don't come into operation until it switches to "closed loop". C5's have four O2 sensors stock and you normally loose two with long tube headers and no CATs. It's recommended to use the rear O2 sensors as they are faster reacting and you have to use an adaptor harness from Lingenfelter or???. This is all from memory as it's been a few years.

Another thought, if the motor runs good for the first few minutes after start up and then goes sour, disconnect the MAF to keep the motor in open loop, if it cures the problem, the burnt O2 harness is shorting out one or both O2 sensors. When you had the big stumble at 70 mph, that could have been because the motor went into reduced power. I think disconnecting the Battery for a minute resets this. Again, it's been a while since I've been there.

Cheers, Curt

 

Curt, your correct. I only have two (2) O2 sensors and they are the rear two with 24" long harness extensions from Texas Speed as are the headers. I have disconnected the battery and reconnected it when I was fiddling around with the PCM connections just to be safe, so that step is out of the way. I am cautious of disconnecting the MAF. With a supercharger on the car, and the car supposedly tuned for it, won't the car run all F';#*d up even at idle without the MAF connected ? I know that the blow off valve should be wide open at idle to dump the excess pressure in the charge tubes, but, just not sure here. Educate me a little, what is the "open loop" scenario you mention ? How does the car know how much fuel to inject without the MAF connected ?

Thanks

 

Modern fuel injected cars use 2 modes to run in. When COLD they run in a preprogrammed RICH mode called OPEN LOOP. Data from the O2 sensors is generally ignored and a preset fuel map is used. As the engine comes up to temp, the computer goes into CLOSED loop mode, adjusting the fuel mixture from inputs recieved from the O2 sensors (as well as others). It becomes a CLOSED FEEDBACK LOOP at that point. The front O2 sensors are generally used for this activity and the rears are used to determine catalyst efficiency.

 

dougbfresh described it perfectly .....

 

And Jeff will know in time.........I guess maybe wiring/tune issue. Hold the phone closer so I can see it

 

You guys are great for my education on this car. Up until now I had only built normally aspirated street rods several of which were blown and over 900 HP. However, this is a whole new ball game for me. Jeff and his team have also been really great so far, they have taken the time to keep me posted and talk to me if I stopped by or called. I have no doubt that they'll get it right.

I think I understand the "closed vs open loop scenario", but need some clarification on my understanding of how the components are working together with a couple of questions.

- If the car is in open loop scenario when first started and warming up, this means that the info from the O2 sensors is ignored and a preset fuel map is used. Does the MAF unit not come into play here at all during the open loop stage?. For instance what happens if you just started the car, put it in gear and tried to drive it by putting your foot on the gas while cold. I assume the chain of events to be: signal the throttle body to open, MAF unit to sense more air flow, and injectors to inject more fuel. If the MAF unit is disconnected and the O2 sensors ignored, how does the car know how much fuel to inject ? Does the throttle position sensor take up the reins. ?

- Does disconnecting the MAF unit truly signal the car to stay in open loop mode?

- There was mention of disconnnecting the MAF unit to diagnose the O2 sensor problem, as indicated by the car not stalling once warmed up. Is there any potential for a lean / rich mixture problem occuring at any point in this testing procedure.

- I understand there to be a air valve at the back of the motor, behind the intake manifold that is a bastard to get to that can often be a cause of some of these problems. I have also heard of spraying WD40 into one of the vacuum hoses upstream of it to loosen it and keep it from sticking. As I am making a list for myself of legitimate planned maintenance issues to tackle on this car once I get it back, do I need to add this to the list ?

Thanks everyone

 

What about the harness on the motor that rubs through and shorts out? There are some threads about it in search.

 

Scott, go to this link, HP Tuners forum, you'll find all your answers.

http://www.hptuners.com/forum/showthread.php?t=4742

Cheers, Curt

 

Ahhhhhh, and the wealth of info pours in. Curt, your right, wow!! There are several nights of reading to be had here.

Scott

 

MAF measures the amount of air coming in, the computer makes a "guess" in open loop as to how much fuel to use based on a table (fuel map). It does use MAF and other inputs to try to decide, just not O2 at that point.

 

I was the OG owner of the car before it got SC. It was installed by a shop here in Oregon NOT by MTI. MTI in Houston gave it a real tune as the tune I had it on was a simple "make it drive and not blow up" flash from Andy @ A and A. It made great power at MTI and as far as I know it ran just fine according to people I know at MTI as well as locals. It needed new coilpacks back when I sold it. The O2 extensions were already shaping up to be a problem as well. Those were the only two issues that I personally knew of at the time. I cannot speak with 100% certainty that something happened to it. However the new owner posted a video of it running and called me and let me hear it running on a couple occasions. Just my 2cents. Sorry your having so many issues though man.

You said you replaced the drivers side fuel pump....did you replace it with another Lingenfelter fuel pump? Because that's what I personally installed on the car. So if you replaced it then you are running a stock one now.

 

Scott....

I have a similar problem with my 02 Z06. (see: http://forums.corvetteforum.com/show...ghlight=intake

From what I can tell so far... A vacuum leak is my culprit. Most likely the intake manifold or the map sensor. Next week it goes into the shop and let the "brains" work on it. I'll let you know what I find out. I couldn't find a way to check for vacuum leaks.....

 

Diceman, I did see your post and was monitoring the responses to see if you got it figured out because we seem to be in the same boat problem wise. We believe mine is an electrical problem somewhere, as the car will start and run fine sometimes for a couple of minutes, then go to s#*t, other times it won't start at all even when cold. Drawing a blank on this one, and it's got me furious.

 

I am having similar problems as you walker07. I was wondering the same thing on my 02's because of the heat that comes off my turbos melting the wires. I am very curious about running with the disconnected MAF to see if it helps a little.

My problem is that it feels like the motor is loading up with fuel and falling on its face. The longer I stay on the throttle it will help clear it for a minute but then goes right back to huffing and puffing and then chokes itself out.

I have checked everything I know of and I have nothing.

 

Alex, one thing I have learned for certain so far is that the O2 sensor wires need to be wrapped with heat shields to keep them from melting. Without insulation on the wires, the O2's are useless. Unfortunately this did not prove so far to be the solution to my problems.

 

In closed loop the O2 sensors keep the car at a constant ~14.7:1 air fuel ratio. That is they're sole purpose in life. In open loop, the pcm doesn't take any readings from the O2s, this way it can richen up fuel, sort of like a choke. At approx. 144 degrees engine coolant temp, it goes into closed loop.

MAF works in open loop. If you disconnect the MAF, this is called Speed Density. A lot of guys prefer a speed density tune. The only drawback is, the MAF can sense air density so you fueling is pretty close to the same regardless of weather or temperature. With speed density, your car will run the best at whatever temperature it was when the car was tuned.

Nope.

open loop = no readings from O2s, you can set fueling to whatever you want

closed loop = afr is controlled by 02s and is 14.7 at all times except when you floor it and go into PE (power enrichment) mode, which should be around 11.5:1 on a F/I car.

speed density = no MAF

disconnecting the MAF has no affect on the O2s. One thing you can do is remove one of the narrowband O2s and replace it with your LM1. The LM1 has the capability of simulating a narrowband. This way you can still run the car as normal, but have the wideband too. This way you will always know what the afr is. The LM1 has an analog output that goes to your wiring harness that connected to the O2 that you removed. Check your paperwork or Innovative website for proper wiring. I have run my car like this for over a year with the wideband O2 in the passenger side header.