Any TBI gurus on here

What sort of issues are you having?
 
Caver Dave has done a good bit of research while putting a few setups together.
 
The engine is originally from a 1993 Suburban, I have some specs on the engine, the block has been bored .040 over,heads resurfaced .007, it has flat top pistons (h-345acp-040), a (cs-1014-r) camshaft, a tbi spacer and injector spacer and a lower temp thermostat. I also installed a complete accel ignition system (wires,coil,cap and rotor), and a aftermarket oil pump(m55hv). The saddle tanks have been removed and a fuel cell has been installed with a Holley TBI fuel pump. I have installed a 2 1/4 true dual exhaust system and have kept the original emissions systems. I'm having a problem currently with when the vehicle is in gear it stumbles but when I have it in park or neutral it revs up fine. Any input on this issue would be greatly appreciated.
 
I spoke with Harris performance in Randleman and he suggested a heated oxygen sensor and a custom tuned chip which I'll probably do regardless. When I get the truck back from Marsfab, I'm going to hookup an air/fuel meter and attempt to see what the engine is up to.
 
NCDieselWrench said:
I spoke with Harris performance in Randleman and he suggested a heated oxygen sensor and a custom tuned chip which I'll probably do regardless. When I get the truck back from Marsfab, I'm going to hookup an air/fuel meter and attempt to see what the engine is up to.
Click to expand...
Fuel trims or a correctly reading O2 sensor and map readings would be the best way to find the issue from my experience.
 
NCDieselWrench said:
Should I get the aldl cables and software?
Click to expand...
Yes because a datalog needs to be run for a custom tune to be done and a heated o2 sensor will really help speed up the readings.

Buckeye Performance Inc.
828-779-2242
 
I'd start by checking the fuel pressure and volume too. It won't take much fuel to idle or free rev but will need more fuel under load. After that id start datalogging and checking sensor outputs
 
I was thinking about checking the fuel pressure, what would be the best way and how do I determine if it's a weak pump or a weak regulator? I was thinking if the reading shows weak to replace the regulator first cause it's cheaper.
 
Last edited:
You'll have to tee into the fuel pressure line or use an adapter that comes with some fuel pressure gauges. TBI doesn't have a test port stock. Specs are 9-13 psi but I've seen drivability issues at 9 so I like to see 11-15. I like to check the return line flow also. If there's not much fuel flowing in the return line it typically means the pump can barely keep up if pressure is good. Odds are it'll be a pump over a regulator but if pressure is low pinch off the return line momentarily and see if the pressure spikes. If it does it would be a regulator stuck open or spring broke. If it doesn't spike then the pump is bad.
 
Pull plugs and verify that the timing mark is on 0 when cylinder #1 is at tdc. That ensures setting the timing is at the correct degree to the crank. On multiple occasions I have seen the outer shell of the harmonic balancer slip on the inner part, only enough to throw timing way off but not enough to slip continuously.

Also check and re check all grounds.

Install a 195 thermostat. I know a cooler one will richer the engine but if you are going to datalog and get a chip burnt go back with 195. Your heads will thank you for not having water temp constantly swing from 160-210 all the time.

Also make sure you correctly set the base idle speed, in gear with engine warm holding the brake.

Make sure when you set the idle speed the tps voltage is .54-.6 volts at idle. There is a process to this and if you are interested let me know and I will post it. It's a series of events to ensure IAC is closed completely, and then unplug it to set base idle.

While you are checking fuel pressure, also check vacuum and post all the info. Vacuum dropping due to valve overlap will cause the map sensor to think the load is increasing and richer the mixture.

Two ways to go from here and you may go both directions to verify and cross check all your info.

Take some .030" wire like welding or bailing wire and attach it to a voltmeter and back probe all the sensors and read what voltage is going to the PCM. One wire is 5 volt supplied from PCM, one wire is ground to PCM and one wire is the signal wire and that's what you are looking for.

Post all the voltages you have on each sensor when
Key on engine off, throttle closed
Key on engine off throttle wide open
Key on engine running

As well as vacuum and fuel pressure at idle.

All of the info you are looking for is also available through a datalogger and aldl cable.

After ensuring all your sensors are performing to spec,
And everything is set up correctly, timing, base idle, tps voltage at idle, etc, and all grounds are good and it's not a fuel feed or return issue,

Then you are after the integrator numbers and blm numbers that will show how rich or lean it is.

stoich is 128 for both, the integrator is short term fuel corrections, the blm is the long term. If the blm is below 128, the PCM is trying to remove fuel due to a rich condition. If the blm is above 128, the PCM is trying to add fuel due to a lean condition. The father the integrator is from 128, the faster the blm will change.

So if you get the data logger up and running take note of all the sensor values above, as well as

The integrator and blm value and what blm cell those numbers are in. This info will be invaluable to the tuner.

If you get numbers at the end of the scale for blm, ex: blm min is 105, and stays there for extended period, this confirms that the PCM "understands" the engine is rich and has pulled all the fuel it can, and is still rich. The PCM will then kick an error code for rich.

Post the info you come up with. Feel free to txt or call me if you get stumbled I'll be glad to help.

Scott
2 five 2 nine 0 3 nine nine 6 2
 
Mac5005 said:
Pull plugs and verify that the timing mark is on 0 when cylinder #1 is at tdc. That ensures setting the timing is at the correct degree to the crank. On multiple occasions I have seen the outer shell of the harmonic balancer slip on the inner part, only enough to throw timing way off but not enough to slip continuously.

Also check and re check all grounds.

Install a 195 thermostat. I know a cooler one will richer the engine but if you are going to datalog and get a chip burnt go back with 195. Your heads will thank you for not having water temp constantly swing from 160-210 all the time.

Also make sure you correctly set the base idle speed, in gear with engine warm holding the brake.

Make sure when you set the idle speed the tps voltage is .54-.6 volts at idle. There is a process to this and if you are interested let me know and I will post it. It's a series of events to ensure IAC is closed completely, and then unplug it to set base idle.

While you are checking fuel pressure, also check vacuum and post all the info. Vacuum dropping due to valve overlap will cause the map sensor to think the load is increasing and richer the mixture.

Two ways to go from here and you may go both directions to verify and cross check all your info.

Take some .030" wire like welding or bailing wire and attach it to a voltmeter and back probe all the sensors and read what voltage is going to the PCM. One wire is 5 volt supplied from PCM, one wire is ground to PCM and one wire is the signal wire and that's what you are looking for.

Post all the voltages you have on each sensor when
Key on engine off, throttle closed
Key on engine off throttle wide open
Key on engine running

As well as vacuum and fuel pressure at idle.

All of the info you are looking for is also available through a datalogger and aldl cable.

After ensuring all your sensors are performing to spec,
And everything is set up correctly, timing, base idle, tps voltage at idle, etc, and all grounds are good and it's not a fuel feed or return issue,

Then you are after the integrator numbers and blm numbers that will show how rich or lean it is.

stoich is 128 for both, the integrator is short term fuel corrections, the blm is the long term. If the blm is below 128, the PCM is trying to remove fuel due to a rich condition. If the blm is above 128, the PCM is trying to add fuel due to a lean condition. The father the integrator is from 128, the faster the blm will change.

So if you get the data logger up and running take note of all the sensor values above, as well as

The integrator and blm value and what blm cell those numbers are in. This info will be invaluable to the tuner.

If you get numbers at the end of the scale for blm, ex: blm min is 105, and stays there for extended period, this confirms that the PCM "understands" the engine is rich and has pulled all the fuel it can, and is still rich. The PCM will then kick an error code for rich.

Post the info you come up with. Feel free to txt or call me if you get stumbled I'll be glad to help.

Scott
2 five 2 nine 0 3 nine nine 6 2
Click to expand...
I think I'd go the data log route. It'll pay off in the long run? Not to mention saving the aggravation of checking fuel pressure unless it's absolutely required lol.
 
ImageUploadedByTapatalk1399248844.909308.jpg
ImageUploadedByTapatalk1399248854.963987.jpg


This is what I use to check fuel pressure on most gm vehicles, especially tbi.

Silver soldered a refrigeration shrader valve into an open area on a spare filter. Cut an old filter open to ensure this was a good area to put port.
 
So the aldl cable showed up but I have to wait until I can get my laptop back from my neighbor so I can run the log. I'll update ASAP and thank you for all the suggestions so far! FYI autozone rents a tool kit to check fuel pressures and it has the adapter for tbi, just in case.
 
Harris Performance/TBI Chips sells chips and other parts for tbi systems. He also makes custom chips. I was in the process of installing a set of vortec heads on my 1995 2500 using info from his site. We were going to put my truck on a dyno and make a custom chip. I got all the parts together but ended up selling the truck before I got time to do the work.
 
Mac5005 said:
Take some .030" wire like welding or bailing wire and attach it to a voltmeter and back probe all the sensors and read what voltage is going to the PCM. One wire is 5 volt supplied from PCM, one wire is ground to PCM and one wire is the signal wire and that's what you are looking for.

Post all the voltages you have on each sensor when
Key on engine off, throttle closed
Key on engine off throttle wide open
Key on engine running

As well as vacuum and fuel pressure at idle.

All of the info you are looking for is also available through a datalogger and aldl cable.
Click to expand...

A little something I created (when I was setting up my TBI swap) to keep track of all the various voltages... HTH
 

Attachments

  • 1227747 Voltage Checks.zip
    7.5 KB · Views: 412
Since my neighbor is using my laptop, one of my friends offered up his snap on scanner. He said it has all the bells and whistles, so I'll be hooking that up this weekend and maybe see whats going on
 
NCDieselWrench said:
Since my neighbor is using my laptop, one of my friends offered up his snap on scanner. He said it has all the bells and whistles, so I'll be hooking that up this weekend and maybe see whats going on
Click to expand...
That scanner is useless as compared to the winaldl program on a tbi engine.

Buckeye Performance Inc.
828-779-2242
 
Back
Top