Frankenstein TBI Fuel Pressure

[94x4 blazer]

after doing the ultimate TBI mods on a 350 TBI i put the injector assembly on a 454 TBI base but after doing so ive noticed that my throttle response coming off the line is very sluggish. do i need to raise my fuel pressure to keep up with the massive increase of airflow? does anyone make a gauge to check the fuel pressure? i made my stock fuel pressure reg. adjustable and my only worry is that because i cant see how many lbs of pressure im running ill increase it too much and mess something else up. thanks.

[mounty]

what all is done to your engine?

if all you had done was mod the tbi and swap injector pod from a 454 tbi then you are dumping wayy too much fuel for a stock 350.
put the 350 injectors back in and raise the fuel pressure a turn or two. should be golden. :)

[ryan_thompson87]

He has the 350 injectors in it, just on a Big block base. Yes you need more fuel pressure. You really can't hurt anything by increasing pressure, the stock pump won't put out enough to hurt anything. Pick up a cheap fuel pressure gauge, and one of these http://cgi.ebay.com/ebaymotors/GM-TBI-Crossfire-fuel-pressure-gauge-tap-1984-95-_W0QQcmdZViewItemQQhashZitem35b00d44fcQQitemZ23058 6926332QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries anyway, comes in handy alot.

[oldred95]

Its needs more AE TPS not necessarily more fuel pressure. Requires tuning.

[helo]

x2 needs tuning. AE map and AE tps will resolve your issue. If you aren't prepared to tune, you'll need to put the 350 TB back on there for now. Adding a lot of fuel pressure may eliminate your sluggish feel off the line, but then it'll throw you for a loop for all other running conditions and you'll end up significantly worse off at idle/cruise/decel/etc...

Personal experience, when I went to a '96 motor (tbi-vortec), I got to 45psi with stock prom before my sluggish start went away. It was running stupid rich. It's all about AE, not fuel pressure. (a guy on thirdgen told me to keep upping fuel pressure until it ran right and then play with the tune; WRONG)

As I keep explaining to my uncle, it's not a carb; you can't just increase/reduce fueling with a screw and expect it to run better across the board.

[94x4 blazer]

my engine is bored 40 over with a pretty hot cam an open intake and a high flow exaust. i ran the 454 injectors for a little bit and then realized that it was an overkill and made me run waaay too rich. im up for whatever tuning i need to do but i dont know what AE stands for. thank yall.

[someotherguy]

It's still a good troubleshooting tool to KNOW your fuel pressure, I don't think anybody would argue with that.

What I'll add is to skip buying that T from the link posted, those guys are charging 3X what that part actually costs. I made the mistake of buying it from them and then was shown where it can be had for much cheaper.

Actron sells a gauge kit with that T included, and if you hunt around, you'll see the T itself listed for about $10 - not $30 like XtremFI gets for it. The part, #0180-000-1320 is listed on Actron's site for less than $7! Searching for that part # on google I found it for $10ish from Toolsource.

Here's one of the kits that includes it:
http://www.someotherplace.com/tools/actron7817_fuelpressure.jpg

Here it is in action...for a permanent type install. Or, you can just put it in down by the filter. Obviously when leaving it in place permanently, you'll want to score a cap for the valve so dirt doesn't get in it. The cap used on a Vortec setup's test port is the same fit.
http://www.someotherplace.com/guides/fueltee.jpg

Richard

[helo]

my engine is bored 40 over with a pretty hot cam an open intake and a high flow exaust. i ran the 454 injectors for a little bit and then realized that it was an overkill and made me run waaay too rich. im up for whatever tuning i need to do but i dont know what AE stands for. thank yall.

Acceleration Enrichment. What ECU do you have? (I don't see that you posted a truck/year, just 454tbi)

AE TPS is a burst of fuel when the TPS changes, and AE MAP is a second burst of fuel when the MAP changes. Depending on how much change the ECU measures, the duration of the fuel shot varies (adjustable). Too much AE and you get a slight hesitation with black smoke; too little and you get a horrible bog off idle and perhaps a backfire out the intake if you give it too much pedal.

Start by doubling or even trippling the lower end of your AE tables. Anything less is just pissing into the wind.

[Fast305]

x2 needs tuning. AE map and AE tps will resolve your issue. If you aren't prepared to tune, you'll need to put the 350 TB back on there for now. Adding a lot of fuel pressure may eliminate your sluggish feel off the line, but then it'll throw you for a loop for all other running conditions and you'll end up significantly worse off at idle/cruise/decel/etc...

Personal experience, when I went to a '96 motor (tbi-vortec), I got to 45psi with stock prom before my sluggish start went away. It was running stupid rich. It's all about AE, not fuel pressure. (a guy on thirdgen told me to keep upping fuel pressure until it ran right and then play with the tune; WRONG)

As I keep explaining to my uncle, it's not a carb; you can't just increase/reduce fueling with a screw and expect it to run better across the board.

They probably told you to adjust/raise fuel pressure to make the WOT fuel correct. The TBI ECMs are fairly close to having the useable pulsewidth on the factory injectors used up by 4,500 rpm, much less 5,000. To rais the RPM you can turn the engine you have to raise the fuel pressure. A 260 HP engine needs around 20 PSI with stock injectors and a 300 HP engine needs around 30 PSI.

[Fast305]

Acceleration Enrichment. What ECU do you have? (I don't see that you posted a truck/year, just 454tbi)

AE TPS is a burst of fuel when the TPS changes, and AE MAP is a second burst of fuel when the MAP changes. Depending on how much change the ECU measures, the duration of the fuel shot varies (adjustable). Too much AE and you get a slight hesitation with black smoke; too little and you get a horrible bog off idle and perhaps a backfire out the intake if you give it too much pedal.

Start by doubling or even trippling the lower end of your AE tables. Anything less is just pissing into the wind.

I wouldn't touch AE MAP, just TPS AE. You are not changing the intake manifold so it doesn't need more AE MAP. Only needs a slight amount more TPS AE due to the larger throttle plates. Too much MAP AE and the truck will bog on part-throttle upshifts.

[94x4 blazer]

Acceleration Enrichment. What ECU do you have? (I don't see that you posted a truck/year, just 454tbi)

i drive a 1994 blazer but the base of my tbi is off a 92 i beleive. i not sure which ECU i have i guess whichever one came stock in 94.

how do you go about change the AE on your TPS and MAP?

[1.721afr]

how do you go about change the AE on your TPS and MAP?

By changing the settings in the associated tables...time to do a good bit of study.

Start by reading ALL tuning stickies.

BTW your "hot" .040" over 350 never needed a big block TB.:twak:

[whitelightnin92]

the bbc tbi will get you a good bit more power over 5k. given you have good flowing heads and cam.

[94x4 blazer]

By changing the settings in the associated tables...time to do a good bit of study.

Start by reading ALL tuning stickies.

BTW your "hot" .040" over 350 never needed a big block TB.:twak:

yes i now realize that i never needed that much fuel. my engine was just wasting it. i guess its time to read...

[94x4 blazer]

the bbc tbi will get you a good bit more power over 5k. given you have good flowing heads and cam.

ive got a good cam in it. but stock heads, i just cant see spending the 670 that jegs wants for a set of after market ones. do you know anywhere i could get some considerably cheaper?