I instlled a Air Fuel ratio this week end and is showing running lean at highway speed causing a run hot problem. It is a 79 with 383 TPI installed. I am running a 7730 ecm with a map system. 24 lbs injectiors, 10* advance,and a adjustable fuel pressure regulator. I have set about 50# fuel with no vacuum. Any ideas how to richen up the fuel system...

 

There are three ways:
-reburn the EPROM with new fuel curves
-bump fuel pressure to 55psi, if that's enough??
-install larger injectors

But you really need a way of checking A/F under various conditions. A scan tool will do this, even the stock O2 sensor.

 

toyvette, off the cuff your performance has to be way off. setting a global timing curve @ 10* BTDC might be too much, definitely the 50psi fp setting w/o vacuum line at idle means you're running somewhere in the 57-60 psi range which is waaaaay too much.

since you're running MAP strategy its criticial that the chip be recalibrated extensively. i'll bet your timing and a/f values are all over the board.

i would recommend Alvin at www.pcmforless.com, whom i'm sure will help you very well indeed with your chip recalibration, so there's no worries. your timing and fp can then be brought back to sane levels as well.......the sooner the better. good luck!

 

Bradvette, doesnt the fuel pressure go down when vacuum is applied, so when you open the throttle and vacuum drops it increases fuel pressure. Or an I thinking backward. 50# = 42# under vacuum.

I have a PCMFORLESS prom in the car, but the Alvin only gives you a piggy back module and I dont know what is on the original prom itself or ware it came from. So I ordered a prom from Proms by Jim and it has been sent back with very little change in performance. I will probley send what I have out of the car to Alvin and see if he can make heads or tales out of it.

I have scan tool but am not sure what I am looking at..

 

toyvet, yes you're correct on the fp reading, my mistake.....42-43psi w/line connected sounds just about right.

you're right to keep working with alvin on your piggyback, as well as determining what main chip is all about. i believe the '90-92 TPI cars use the very same ECM you have (MAP), and it sounds like you just need some more work on that piggyback.

just off the top though, that 10* advance timing sounds like it could be risky. are you getting alot of knock counts/spark retard? again, i would work with alvin to get the tuning squared away - he's an excellent tuner

you have quite a hybrid of a vette there!

 

What do you mean by lean? If you installed one of those narow band ratio meters, they dont really tell you anything meaningfull. If you think its lean because it's alternating rich/lean, it's probably not. That's normal output of the o2 sensor in closed loop with proper fuel control. And those cheapie gauges are just voltmeters with leds, measuring the o2 output.

 

Yes it is a Autometer gauge. At low speed it will bounce equal lean to rich. But at highway cruise speed it will peg lean and only go mid on the normal range. The engine temp will climb to 215* from 180*. I never had this problem until the TPI was installed.

 

It does sound like its a little lean even though I don't like the AFR Meters that Auto Meter and others sell. As these are not true AFR meters. All they do is monitor the O2 sensor voltage. It is normal for the voltage of a narrow band O2 sensor to vary from rich to lean or from about 200mV to 800mV during normal cruise and light throttle. But the thing about narrow band sensors is that they operate in a narrow region of voltage to indicate 14.7 AFR, which is 450mV. You need a wide band or otherwise referred to as a linear output sensor to indicate true AFR. A typical wide band system has a 0 to 5 volt output.

Check them out here:

www.innovatemotorsports.com

If you have a scan tool, observe the long and short term fuel trims. If they are going to say 135+ then the ECM is attempting to add fuel. Observe this when under the same conditions during cruise where you mentioned that the Auto Meter gauge is indicating lean. This would back up its indication of a lean condition. The ECM has a limit that it can add fuel with the fuel trims. Usually it pegs at around 160 and 108 on the other end of the spectrum. When the O2 sensor tells the ECM that its lean or rich the ECM responds by taking fuel out or adding fuel. The smaller the fuel trim number the more fuel it is taking out, the larger the number the more its adding fuel.

Depending on your scan tool, the fuel trims can be referred to as Long and Short term fuel trims or it can be referred to as Integrator or INT and Block Learn Multiplier or BLM.

 

I checked fuel prussure this morning. Adjusted fuel pressure to 50# no vacuum. 44# with engine at idle and vaccuum applied. Run the engine up to 3500 rpm and fuel pressure drops to 44#. Shouldnt pressure increase as engine speed increases and vacuum drops. I only get a small flutter in fuel pressure under acceleration and it settles back at 44#. New AC 241 fuel pump, new regulator, new ac fuel filter,new adjustable pressure cap(?).Pump will put out 60# no vacuum when check for max pressure. Any ideas??????

 

Yes, fuel pressure should rise as manifold vacuum drops. If you're just free reving to 3500rpm, then manifold vacuum is still high, maybe even higher than idle. Test drive it with the gauge installed and note if pressure drops under heavy load.

 

Is the ECM calibration setup for hiway lean cruise mode? This may explain the lean running. Else, is the ECM still in closed loop?

Al.

 

Took car for ride and fuel pressure was pretty much stable within 3 or 4 lbs. Also unplugged vacuum at regulator and plugged line. Running 55# full time at highway speed and still same problem. Yes it is in closed loop. I am baffled as whats going on. No way I can believe it is starving for fuel at 55# pressure? I will do some testing in the am.........

 

With the scan tool you can monitor BLM cell number and cell value as well as INT value along with O2 sensor values.

During steady cruize conditions these values should be very close to 128; when you go to WOT the BLM cell number should go to 15 with a value of 128 and the INT value should also go to 128.

Also, under steady cruize conditions, the O2 sensor values should swing between say .9 to .3 Vdc and the ECM should show closed loop mode. When you go to WOT the mode should stay closed loop but the O2 sensor value should go to around .89-.92 Vdc.

 

65Z06 thanks, I.ll try it out in the am and see what the scanner does....