Hey all, still new to the prom tuning, but I searched and I'm SOL. What I have is a 350 horse vortec 350 comp extreme fi cam. 747 ecm, $42 mask, BBC TB w/90pph injectors.

Here's the issue, I mash the throttle, 1st gear, 2nd comes fast, 3rd after that, about 2800 rpm or so, it seems to slow down, less pull. If I let up on the throttle some it pulls again. Any idea's??

Been messing with the SA tables, coolant comp, and what not. still learning to understand the PE. Anybody had this happen?? What should I do to fix it?? Thanx all.

 

When it's slowing, what does the narrow band O2 sensor read? If it's still above 600mV, I'd guess you're way too rich. But, since you only have 90's in large cam engine, you may be leaning out already, or don't have the calibration right yet, and should be seeing <200mV on the O2 sensor.

Total PE should be in the 14-20% range, on an NA car. VE should be set first to get approximately stoich 14.7 if you plan to run closed loop. If you plan to run Open Loop all the time, you can set the high loads to either the full richness and not use PE, or set it to a little rich, and get more enrichment with PE (probably better economy this way, and better if you change altitudes a lot).
If you're running closed loop, you don't necessarily have to set the high RPM VE to 14.7, since almost no time is spent up there while still in closed loop. But, if you don't have a wideband, it's the easiest way to tune. Seat of the pants will be a waste of gas.

If it's a spark timing problem or general ignition problem, it would have to be serious to cause these symptoms, so I'll assume for now that it's not that.

 

well, I'm using closed loop. Don't have a wideband yet. And I'll have to make another run to make sure the o2 is up there @800-900mv. It's hard to look at the scanner and drive. I'm emulating using the moates autoprom and tuner pro rt. I know seat of the pants is a waste of time, but in first and second it screams, then in third it dies off till I let out of the throttle, the picks up speed. I don't fully understand the whole PE yet, That may be where my problem lies. I set my BPW @ 100, and been playing with the AE tables. Was rich low and lean high. FP is @ 12-13psi W/stock regulator. I used the LT1 SA table, hot spark is 0, cold is 7, and changed the coolant comp so it's the same in he normal areas as the cold is. base timing is 8 btc, if i understand right, it is subtracted from the main SA table.

 

Well,

Timing shown in Main spark table IS the timing the engine gets, when warm.

Coolant SA Table - Coolant SA Bias = Offset to Main SA Table
(Note: You CAN be set up TP RT4 to subtract the bias from the table and display the actual offset for you, then won't need to mentally subtract it)

There is a temperature at which the coolant offset stuff is disabled.

PE offset gets added to the Main SA Table.

Base Timing = Base timing. Set it to actual, and the rest of the tables automatically do their job. Don't mentally add or subtract it to anything.

If any of this is different on the 7747 than what I say, someone please jump in and correct it.

 

Coolant SA Table - Coolant SA Bias = Offset to Main SA Table
(Note: You CAN be set up TP RT4 to subtract the bias from the table and display the actual offset for you, then won't need to mentally subtract it)

There is a temperature at which the coolant offset stuff is disabled

Thank you for that bit of info there, there other few things I understand. Over time the fog is lifting, lol. Maybe i have too much timing. I could zero out the PE timing table. It just seems like if I let off to half throttle it pics up speed faster.

 

The coolant offset stuff doesn't ever get disabled. Typically the coolant compensation is set to be 0 at normal operating temperatures (but not always on stock bins).

By letting off to half throttle is the ECM dropping out of PE mode? If so, that may be a sign of too rich when at WOT.

Are you truely running a VAFPR with the fuel pressure set to 13 psi? Is that 13 psi with the vacuum line disconencted? I don't think that it is needed at that low a pressure.

RBob.

 

Is that just for 7747? My $6E .ecu/xdf has a coolant temp spark correction disable temperature. Haven't checked others, just assumed it was likely there.

 

Not necessarily only for the '7747, as other ECMs are the same way. The coolant compensation table is always in affect ('7747 along with others). There is no cold or hot start SA modifiers on the '7747 as some TPI masks have. There is start up SA that is added (some times referred to choke SA). This is decayed out over time.

For the best information on how the '7747 SA operates there is a paper floating that describes most if not all of the parameters.

RBob.

 

That sounds like either too much timing or a weak fuel pump/lean condition. Maybe even both. I hope you've got a good fuel pump as in non-TBI and it's relatively new (not older than 3 years and a clean filter).
Hook up a scanner and even with the 160baud rate you should be able to see the knock counter go up when in 3rd gear pull IF it's too much timing. Get back to us with the test results and we can go from there.

 

well, was driving today, and before my laptop batt died I noticed a few things,

a: I get no knock counts, EVER, I think the knock sensor is bad.
b: My O2 is lazy, I think.

If I watch the BLM's, they may be @ 120, but the O2 will swing from 10mv to 600 mv and sometimes stay on the really low side.

I'll change that tomorrow.


I took it off because the FP was really high @ idle with the supplied spring, I'll have to get the other spring to use it again. I am using the stock FPR for a 454.

The pump is a new aftermarket mounted on the frame, carter with 220 lph @ 22 psi. The tank is sumped and there is 3/8 line for the feed and return.

I'll have to make the stock FP adjustable I think. See, it's hard to trust my o2 now I think because it is acting lazy. I'll change it and go from there. I'll change the knock sensor too. Beings I have no knock counts even if I bump the timing up.

 

Is there an operational SES light? Do you hear knock?

RBob.

 

actually, I haven't hooked the ground up to the light bulb for the ses. Though the entire time I have a snap on mt 2500 hooked up to the vehicle. I haven't heard any knock, but it's hard to tell with the super 40 mufflers.

 

Any chance the scan tool is showing a code 43? The reason I ask about the SES is that it the forced knock test may be getting invoked. If it fails timing is pulled and the SES comes on.

As the forced knock test is run a lot of timing is added. This can account for how the engine is running. The scan tool should also be in 'open' mode, not any of the diagnostic modes.

RBob.