96-00 5.7 vortec, supercharger tuning help

[hypntyz]

This is a long read, but please bear with me. I am an experienced rotary engine guy and know a lot about custom tuning and turbo installs, but I have no experience with v8s or GM computer tendencies and layouts. I need help with this one, or I'll be forced to abandon the project and go back stock.

 

I have a 99 denali with the 350 vortec engine. This is the version with the internal fuel injectors in each intake runner, the central injector spider setup. I dont know of any aftermarket for this injector setup.

 

I bought a used paxton novi 2000 supercharger setup for it...it was a bolt on kit made back when the trucks were new, but is no longer sold or supported whatsoever. The kit came with it's own fuel and computer setup. Two additional injectors mounted on the throttle hat were activated by the computer to add fuel under boost.

 

First, I had no wiring instructions to go on...paxton claims to have no records of the manuals on this kit. It makes it worse that they changed the electronics at least 3 times during the run of this kit, and I apparently have the earliest version. I did get the thing to come on and light up at various boost levels, but it never triggered the injectors.

 

I removed that setup in favor of an HKS additional injector controller which I can tune myself, and is probably more accurate anyway. I also have a full MSD ignition setup including BTM, 6A, coil, 8.5mm wires. I have the stock cats cut out of the exhaust, and "simulators" in place of the rear o2 sensors. Finally I have a PLX wideband in one of the rear o2 sensor holes and a realtime display inside.

 

even in stock form (I ran it NA for a while to get a baseline) this engine runs 14.6-14.9 air fuel ratio ALL THE TIME. The ONLY time it varies from this is on zero throttle decel after 4 seconds, when it goes full lean. And on WOT accel after 2 seconds it drops to 12.5-12.8 AFR. Any other time, it stays at 14.7.

 

With the blower installed, the idle is rough and it surges a bit at times. AFR stays at 14.5-14.9, and when it surges it might lean out to 15.5-16.0. NO big deal, though.

 

Under boost it stays at 14.7, unassisted by the AIC. I see a max of 7-8psi with the current pulley. I'd like to drop down to a smaller pulley for better response on the low end, but Im afraid to, for the reason below.

 

With the AIC operating and injecting more fuel, I still see exactly 14.7 at all times. It does not even go rich for a split second when the AIC comes on. The AIC has a test feature which dumps fuel in at idle to verify that it works, and I have confirmed that it is injecting fuel. If I go 100% WOT with it, I do see it drop down to 12.8 AFR or so, which is exactly how it behaved without the blower or AIC.

 

So why, even with the AIC dumping in extra fuel, are my AFR's staying so high? I am told I should be tuning for about 12.0-12.3AFR under boost conditions.

 

My only guess is that the stock computer sees the extra fuel via the front 2 o2 sensors, and pulls fuel from the main injectors to lean it back out where it wants to be.

 

Paxton apparently did testing and tuning to arrive at their solution...dump in more fuel at the throttle body. My testing shows this to be useless...how can this be? Their computer setup did NOT interface with the stock engine computer at all...no injector signal, no tach signal, nothing. It used its own seperate map sensor and injector driver. No matter how much fuel gets dumped in, I still get a 14.5+ AFR reading. Surely paxton did not intend it to be this way?

 

Perhaps I should look for a way to disable the main front o2 sensors, to prevent fuel correction? Or is this even possible with this engine setup? Can simulators be used here?

 

Any help would be greatly appreciated.

[Haulin' 8.1]

Hey Kevin welcome to the site. I'm NewRXr on RX7Club where you spend most of your time . I can help you with this like you could help me with my GSL-SE but the thing is it's never a simple two sentence answer as you know. I know you're a very capable tuner it shouldn't matter as you can probably get there your self with some pointers.

 

There is little to no aftermarket on this fuel system, mods would be made with programming. The few actual mods I know of are an intake spacer that adds plenum volume and maybe a larger throttle body.

 

The full lean on coast down is normal programming to conserve fuel.

 

An exhaust leak of any kind before the sensor will cause problems, rule that out first. These manifolds will crack occasionally.

 

To me there seems to be something wrong with the fuel system. I work on these things for a living and have run a lot of test-drives with the computers hooked up. The target part throttle A/F ratio is what you are seeing. But it's not that archaic and you should be seeing an instantaneous fuel ratio response at WOT. The computer learns correction factors and will use them until it sees a change and starts adjusting it's correction factor until the A/F meets it's target. This happens quickly but not instantaneously. I think this is what you are seeing EVERY TIME you change throttle positions. For this to be happening every time you change throttle there has to be something causing a major variable in the system that's confusing the PCM so much that it's always correcting. It could be several things, the intake manifold isn't air tight causing a vacuum and boost leak which screws up everything needed for precise metering, or there is a misfire that's letting unburned O2 into the exhaust system causing erroneous readings, or fuel pressure isn't what the PCM expects it to be. A misfire on this engine could be from any of these things also. What you mention about the rough idle with the blower drive on makes me suspect a misfire condition. In my experience a piston engine will misfire a lot easier than rotary. If the ignition is weak for any reason or the A/F is off by a slimmer margin either way it won’t burn even with the MSD. In fact the MSD may be doing such a good job that it’s hiding it from you most of the time. When a cylinder misses it’s O2 goes into the exhaust and causes the sensor readings to be way off. Your lean readings may actually be due to the ignition and not a fuel supply problem.

 

With the rough idle going on disconnect one plug wire at a time from the plugs until you find a cylinder that isn’t contributing. If you find it look for a vacuum leak affecting that cylinder such as a misaligned intake gasket at the head flange. If you have access to a smoke machine use it to locate any intake leaks. If not use low-pressure compressed air and a spray bottle of soapy water to look for leaks. Make sure the whole system is airtight from the MAF back. Clamp any hose that sees boost or vacuum. If you find the miss but no problems related to A/F ratio on the missing cylinder go over the ignition system thoroughly. Check the cap and rotor condition. Misfires in that cap design are common with age and even on new bargain caps. Ohm the terminals for cross firing; the readings should be infinite between cylinders. You should have installed high quality plugs (not Bosch platinum as boost kills them) one-step colder than stock and reduced the gap at least 0.005” from stock. Use NGK or Nippon Denso’s site to determine the correct plug. I don’t know your mileage but these engines use the distributor pick-up as a cam sensor so wear in components causes the crank/cam sensor relationship to widen over time. After a certain wear point part throttle misfires occur. You have to use a professional grade scan tool to realign them by accessing the “Camshaft Retard” reading and turning the distributor housing until it reads 0* again (= or – 3*). Usually I have to remove the distributor bracket and make the bold hole a slot to provide enough adjustment on a high mileage engine. Double-check your wires with an Ohmmeter.

 

Have you monitored fuel pressure under dynamic conditions? Look up the factory fuel pressure specs. There is a large Schrader valve test port near the distributor on the fuel supply pipe. There is a pressure regulator attached to the spider that is linear in response to internal intake air pressure and should be increasing fuel pressure with throttle and boost and decreasing it when under closed and part throttle. It does so by restricting or bypassing flow from the pump. The problem is that these engines build up sludge in the intake plenum over time and the small port for the regulator may have clogged or the diaphragm inside of it may have a coating now that has slowed or limited it's response. Sometimes the diaphragm has ruptured and drips fuel onto the intake floor causing a rich misfire on cylinders with nearby ports. Also these injectors discharge into a small capillary tube that goes to a poppet valve at each intake port (similar to old school BMW). Often I find one or more of these tubes have melted or ruptured and will spew fuel off uncontrolled causing the effected cylinder to run lean and those near by to the leak to go rich.

 

Here are some things to do, check the fuel pressure and the regulator’s dynamic response. Also make sure the fuel supply system can maintain max pressure at all engine speeds during WOT. It should always rise instantly with throttle opening and boost. The pressure of the system with the pump running and the engine off (intake is at atmospheric pressure) is it’s maximum pressure (without boost) and should be what the listed max spec is. Jump the pump circuit at the relay socket to check the max pressure. If the system can reach the max spec pressure put the relay back on then cycle the key watching for the pressure drop with the engine off. If you can observe the pressure dropping past minimum spec and quickly (within 5 minutes) then the regulator is leaking. If you find nothing there then remove the upper intake plenum and reconnect the fuel lines to the spider as when running. Disable the ignition then have some one crank the engine while you observe the injection system for leaks from the regulator or tubes, or clogged poppets. Afterwards you should install a new plenum gasket set and use silicone grease to lube the seal areas on install. Have several cans of intake/carburetor cleaner on hand as it will be a mess in there and the sealing surfaces have to be clean.

 

I hope this will help you find the reason why the measured A/F ratio is not responding to additional fuel as quickly as it should. If not I would find a way to know for sure the AIC is working under boost.

 

Let me know if there’s anything I can explain something or you run into something else that I didn’t cover. I repair these engines all the time but it’s hard to fix it from here as you know. If I was in Tennessee or you were in Texas we could get together and figure it out in no time. But then I would have been bugging you all last year about why my fuel injected RX7 ran crappy but I eventually got it. The carbureted one was easy.

 

Vernon

[zippy]

my suggestion, get rid of that fuel system, put on an FMU, and change the pcm programming to work with the setup. i've done this already on a 99' tahoe. with the procharger p1sc and the pulley that came on it that truck ran 13.8 the first time out which was less than 24 hours from the time we got it on the road with the blower. you can pull this off on the stock pcm using the FMU, but it's alot easier with the better programmed pcm.

 

 

[runions79]

This is a long read, but please bear with me. I am an experienced rotary engine guy and know a lot about custom tuning and turbo installs, but I have no experience with v8s or GM computer tendencies and layouts. I need help with this one, or I'll be forced to abandon the project and go back stock.

 

I have a 99 denali with the 350 vortec engine. This is the version with the internal fuel injectors in each intake runner, the central injector spider setup. I dont know of any aftermarket for this injector setup.

 

I bought a used paxton novi 2000 supercharger setup for it...it was a bolt on kit made back when the trucks were new, but is no longer sold or supported whatsoever. The kit came with it's own fuel and computer setup. Two additional injectors mounted on the throttle hat were activated by the computer to add fuel under boost.

 

First, I had no wiring instructions to go on...paxton claims to have no records of the manuals on this kit. It makes it worse that they changed the electronics at least 3 times during the run of this kit, and I apparently have the earliest version. I did get the thing to come on and light up at various boost levels, but it never triggered the injectors.

 

I removed that setup in favor of an HKS additional injector controller which I can tune myself, and is probably more accurate anyway. I also have a full MSD ignition setup including BTM, 6A, coil, 8.5mm wires. I have the stock cats cut out of the exhaust, and "simulators" in place of the rear o2 sensors. Finally I have a PLX wideband in one of the rear o2 sensor holes and a realtime display inside.

 

even in stock form (I ran it NA for a while to get a baseline) this engine runs 14.6-14.9 air fuel ratio ALL THE TIME. The ONLY time it varies from this is on zero throttle decel after 4 seconds, when it goes full lean. And on WOT accel after 2 seconds it drops to 12.5-12.8 AFR. Any other time, it stays at 14.7.

 

With the blower installed, the idle is rough and it surges a bit at times. AFR stays at 14.5-14.9, and when it surges it might lean out to 15.5-16.0. NO big deal, though.

 

Under boost it stays at 14.7, unassisted by the AIC. I see a max of 7-8psi with the current pulley. I'd like to drop down to a smaller pulley for better response on the low end, but Im afraid to, for the reason below.

 

With the AIC operating and injecting more fuel, I still see exactly 14.7 at all times. It does not even go rich for a split second when the AIC comes on. The AIC has a test feature which dumps fuel in at idle to verify that it works, and I have confirmed that it is injecting fuel. If I go 100% WOT with it, I do see it drop down to 12.8 AFR or so, which is exactly how it behaved without the blower or AIC.

 

So why, even with the AIC dumping in extra fuel, are my AFR's staying so high? I am told I should be tuning for about 12.0-12.3AFR under boost conditions.

 

My only guess is that the stock computer sees the extra fuel via the front 2 o2 sensors, and pulls fuel from the main injectors to lean it back out where it wants to be.

 

Paxton apparently did testing and tuning to arrive at their solution...dump in more fuel at the throttle body. My testing shows this to be useless...how can this be? Their computer setup did NOT interface with the stock engine computer at all...no injector signal, no tach signal, nothing. It used its own seperate map sensor and injector driver. No matter how much fuel gets dumped in, I still get a 14.5+ AFR reading. Surely paxton did not intend it to be this way?

 

Perhaps I should look for a way to disable the main front o2 sensors, to prevent fuel correction? Or is this even possible with this engine setup? Can simulators be used here?

 

Any help would be greatly appreciated.

[runions79]

I have a lot of experience in your problem. my s-10 had the same problem when i put a turbo on it.The turbo kit had one injector before the throttle body and the air fuel ratio was always high like yours.

My problems were leaking intake gasket under boost in rear drivers side

passenger side o2 was bad

mas airflow (replaced with new larger unit)

after all this my truck had still had a bad idle and air fuel was still high.

I talked to friends who build vw turbo cars and the told me that my truck when in 14.2 to 15.4 when under 1/2 throttle was fine all day long and when under full throttle it went down was wright.

finlly fixed bad idle with 1.7 ratio rockers (same as slitly biger cam) and new head gaskets.

truck ran great up to 18 psi right into a gard rail but that is another story.

Hope any of this helps.