In a C3, typical hotrodder......computer 1227730 aftermarket chips....one is Alvin Anderson, have swapped the chips around among 4 computers, same results all the way.....here is where it gets tricky, the scanner says everything is pretty much normal.....supposed engine temp is same as on the other gauge.....gauge is left front L98 heads, truck 4 bolt main 355, L98 cam, 1.6 on the roller rockers, now here is the trick, a modified LT1 induction to put HEI up top.....done by a welder buddy, and never any signs of any gasket issues, if anything the engine runs very rich, been through many injector sets, they all sound normal with stethascope....even tried a new set....no go.....runs RICH as hell on start.....after engine hits about 150f on both gauge and the computer reader....it smooths out a LOT.....the temp sender goes between 0-5 volts no issue......I have tried adjusting the 'reading' by dropping the voltage or increasing it when engine cold.....no major change air temp sender is just under the intake filter as can be seen in the pix below....

BLM is supposed to be around 128 but it's way above in the 150 range....but I have no idea why.....

the single HEATED O2 sensor seems to cycle back and forth very quickly even when engine is running super rich and stumbling, rough as hell on start up....almost undriveable......

now there is a krazy krap....wife and I took a 3 hour cruise lase weekend in it, top down, and averaged nice operation, 50-70 mph all the way, engine smooth and happy......but this weekend?? all pissed off.....

I have dropped the fuel pressure down to the 24 region, witch smoothed out the full temp running to the point of the enjoyable cruise....it's the slightly chilly start up where I barely get it up hill untill engine warms up that drives me krazy now....

sorry for long post, but more info, hopefully a more accurate response.....

I getting ready to send one of the computers/chip back to Alvin Anderson's outfit and see if they can make anything out about this.....

 

If I am following your post, the rich condition is while it is in open loop but once it goes into closed loop it is fine right? You don't mention the MAP sensor, I assume that is reading correctly?

If so, I think the injectors are not matched to the chip. You can try smaller injectors.

 

YES at one point I thought I caught the MAP as an issue....connector plug in, so replaced it, for sure it's reading what ever I have to ASSume it is correct......

I have tried all sorts of injectors.....being the LT setup with no plastic over the top, they take 4 bolts to change them......I have dropped the fuel pressure to only 24 lbs....with that kind of pressure, HOW in hell any injectors can run RICH when colder but seem marginally rich when warm??

 

Injector size? FPR vacuum port leaking fuel. Vacuum leak? MAP sensor reading at idle? Chips are programmed for intake? Egr? Cat conv?

 

The supposed injector size was 34 but made in China.....getting something made here is over 400 bux/set....not affordable without some iron clad guaranfreekingTEE to fix the issue.....

FPR is fine, one of the early L98 later top adjustable types and so I modified it down to 24 psi to get engine to run decently when hot......I will have to check the voltage on the MAP sensor at idle.....

been so damn long, I forget if the chips were set for the LT induction or the L98......why would it make that much diff at idle??

the longer tubes giving more air then??

seems strange the change to LT induction with a slightly larger t-body would make the engine run RICH, if anything I would guess run leaner.....



no EGR and no CAT....just the HEATED O2 on the pass/right side in the header collector...

 

..... 34# injectors are rather large for a stock build … should be 22's … what is driving the spark control ? …..

 

NOW you got me going.....34# or the pressure #.......somewhere along the line 34 was in the system....
but it WAS the stock pressure of the line....

unsure of the injector flow ratings at this point, have to go back and look....but with 24 for sure on the pressure, why would it run decently when hot/warm, but SO badly when cold.....sounds like a damn diesel and the puffing/misfires are obvious.....much less the black smoke.....

Spartk control is a typical HEI up top, computer controlled, looks normal on the lights......

 

The chip needs to be written with the exact engine combination and parts installed. On Speed Density it is very important.

My opinion would be to get a new chip burned, and make sure the tuner know exacty what is installed.
-If the injector is 34 lbs, that is to large in my opinion.
-Reset the fuel pressure back the the 43.5 psi.

-Make sure the tuner knows the following.....
-Bore, stroke,
-Type of heads, and specifics, valve size, flow rate.
-Cam size, lift, duration.
-Rocker size.
-Injector size, brand, and set fuel pressure.
-Type of intake,
-Type of exhaust manifold,
-Type of exhaust system (stock, true duel, Y pipe exhaust)
-Throttle body size.
-Trans type, and stall with auto.
-Rear gear ratio.
-T stat temp

On Speed density, changing parts without updating the "Chip" will throw the tune off.

 

You need to get the correct Injectors first then reset fuel pressure. It's not worth guessing or send them out have them tested and still buy injectors.. The programming is for 22/24 lbs injectors at 42 psi. The same injector can flow like 60 at 80 psi so it matters. The injector on time is base on what is supposed to be there so it's getting way too much fuel cold before it goes in closed loop.
The TPI intake has different operating characteristics compared to a short ram no different than single plane and a tunnel ram.

 

….. Check the vac line to the fuel pressure regulator … make absolutely certain that there is NO raw fuel in it … put a vac tester on it like a Mity-vac and make sure it holds vacuum … replace the exhaust manifold gaskets to make certain that there is NO free air entering the exhaust and fooling the Oxygen sensor … what ex manifolding is on the car ? Where is the O2S ? make sure the header flange gasket or downpipe donut/gasket is intact with no leaks … the reason it runs like crap cold then smooths out warm is because its going closed loop and the O2S is taking control of the fuel mixture … in open loop the engine is driven by ECM memory … fuel trims … what are the IAC counts at idle ? cold and warm ? What air intake is on the engine ? no restrictions , kinks , crazy bends ? … Has this combo … LT1 in a C3 … ever run right ? … I ask because it could be cam timing or ignition timing issue … How do you set base timing ? The LT motors have no degreed dampers … no keyway to the crank …..

 

Is the blm of 150 in open loop or closed loop? If open loop, blm is set by temperature tables in the programming. I doubt the injectors are the problem, and adjusting the fuel pressure below the recommended 43 psi is not the answer. You need to have a chat with the ecm, by that I mean get some tuning software and watch what the system is doing. I use Tunerpro rt, and it's user friendly. Good luck.

 

Because you have an O2 sensor and are in closed loop when it is warm so it cuts fuel to correct the rich condition.

 

Hello again MrVette,

I suggested that you try another Oxygen sensor to verify that yours is working properly. Even heated oxygen sensors have a 48 month lifespan or 100k miles, the older O2's only had a 24 month/50k miles lifespan. They DO wear out.

As I suggested to you before, the Oxygen sensors frequently fail on the richer side as this keeps a bad O2 from damaging your engine. Most oxygen sensors have a signal that oscillates between .1 and .9 volts. The signal as they age tends to narrow, for example an older O2 might signal between .8 and .3 or some other combination of numbers. The second problem with older O2's is that their signal starts to lag and they can't keep up with the engine RPM accurately. This means that they will run okay at low RPM's and start to cause issues with higher RPMs.

What does your Coolant Temperature Sensor indicate? Not the intake air but the coolant temperature sensor. Does it read correctly? This is a very important sensor that has a lot to do with your engine's operation. If it thinks the car's engine is Hot already then the cold engine will not get additional fuel at start-up and that makes it run poorly. The other way if would have too much fuel at startup and it would be like having a Choke stuck in the "On" position and this would make a hot start very difficult. This sensor is one of the important sensors that helps the ECM make it's air/fuel calculation. Even corrosion on the terminals can make the readings go astray. The readings will give you a resistance Value which corresponds to a specific temperature. If you need the chart it is in the FSM for the C4 Corvettes.

I suspect you have a faulty Oxygen sensor or an issue with your CTS causing your issues. It could be both...

I am wrapping up my installation of my New Holley Sniper Stealth 4150. This system for $1100 will control your engine in a better fashion than what you are playing with now. I wish I had as much control on my L98 as the Holley Sniper gives you. The Holley Software is simple to use and it can do so much. I am getting ready to switch my ignition over to the Holley Sniper as it will control both fuel and ignition and even then you can add progressive Nitrous wet or dry. The Sniper I have looks like a standard old Holley Double Pumper with a couple wires coming out of it. The standard EFI systems today are pretty amazing and if I had problems for a while like you are having with your Corvette I would consider it.

I bought mine from a Company in Central Florida named EFISYSTEMPRO. They provide 2 years of incredible service after a purchase and will have a Holley Tier 3 Technician help get you back on the road reliably. You already have the electric fuel pump system so your out of pocket would be less than a grand for a complete system. You will need an intake manifold to use the EFI simple systems. I looked at the Edlebrock Pro Flo EFI systems with the intake and eight injectors set up like the new Cars are. It has a throttle body for air measurement and would fit under the hood on a lot of cars. Call efisystempro and ask for Chris or A.J. and you will see just how easy and affordable it is to go to a modern fuel injection system.

I hope we can help you discover what is wrong with your Corvette. I would really like to see what happens when you try a different O2.