Audiman

Has anyone experienced any weird driveability issues with their conversions. I worked all the bugs except when in overdrive and putting it to the floor, truck kicks down to 3rd and when it gets to 3500 rpm the r's fall off 200rpm then it just goes back to climbing up again. Second is when pulling a steep hill at about 60, when the engine starts to lug at about 1700 rpm it feels as if there is a slight misfire and sometimes the truck knocks. It used to be way worse before we changed the fuel pump and set the psi at 17. What are you camaro guys running for fuel psi with your vortec heads? Thanks for readin!

kdrolt

The 93 (350, LO5 engine) trucks were rated at 210 fwhp with the TBI. That's probably using 61, 65 or 68 lb/hr injectors. Upping the fuel pressure to 17 psi helped (as you said) but you are still running stock injectors, and you also have a new cam (specs unknown), better intake & exhaust.... plus the Vortecs.

So your engine is now poised to put out somewhere in the 280 to 310 hp range, and probably around 370 to 390 ftlbs, IF it gets the air & fuel it needs. You have what you need to get the airflow but you don't have enough to get the fuel.

You added a chip, you raised the static fuel pressure, but you didn't change the injectors to something larger.

So my advice is that you need to try using the vFPR so that you get more like 20 psi when you get on the throttle, and 16-17 psi at idle & cruise. That will HELP reduce the problem but it may not be enough. You may also have to add larger injectors (ones used on the 454 TBI, they will fit into your TBI) and then reset the fuel pressure. If you do one or both of these things, it will probably correct the major problem you are having, but it won't guarantee optimum performance. To get that you need to do the fuel stuff AND then you need a custom chip. And the one you are using is not optimized for your engine.

The bottom line is that you have a very heavy truck so you are always loading the engine even when you drive easily, and that load is causing the engine to run very poorly. If you keep driving it, as is, you may damage it.

Go back and read the posts (search on TBI) for the vFPR or vaFPR. There are also many posts discussing the need for more fuel, and larger injectors, based on engine mods like yours. And finally, AFTER you work the fuel issues, you might want to go read the FAQ on DIY chip work. Your vehicle has demands that are different than a 3500 lb Fcar so in some ways, your debugging & tuning is going to be different and possibly more challenging than it is for Fcar owners that have done your mods. Lighter cars don't work the engine as hard as your Suburban does.

FYI, HTH. - Ken

Audiman

I am running a custom chip, pace performance had superchips burn me a custom conversion eprom. I already have a jet fuel psi regulator, it is set at 17psi at idle.

DM91RS

Are you running the same intake and heads?

Audiman

I run gm vortec heads off a 96' pickup #12558060. The intake is the gm performance TBI to vortec conversion setup #?, well I cant find it right now, but I am sure you guys have heard about it.:lala:

kevm14

I may be wrong, but I thought the trucks ran 55 lb/hr injectors.

Therefore, he needs that fuel pressure even more.

Assuming he started at 12, and goes to 20psi, that's 20/12 = 1.667, sqrt(1.667) = 1.29 * 210 = 271hp. So 20 isn't bad, but it may or may not be everything the engine wants.

kdrolt

Agreed. And I don't think his custom chip knows diddly about the fuel pressure that he's running, and any place that DOES a custom chip should have asked (a) what injectors will you be using and (b) what fuel pressure will you be running.

If they didn't ask those questions, then you probably don't have an optimized chip for your application. I think my original answers pretty much still stand FWIW. - Ken

Audiman

The people who sell the vortec conversion kit had the chip made. They do hundreds of these conversions and even offer it in their catalog. They have been working with me to figure out these problems, I think upgraded injectors are the next step.

DM91RS

This it?

Audiman

Yes, that is it! I talked to mark at Pace this morning and I think we will run 454 injectors and turn down the psi on the regulator.KDROLT how did you get that formula and what does it work out to with 85 lb?hr injectors at 15psi. How do you figure it out? Are the 454 injectors 85 pounders?

kevm14

Here, take out the guess work with this:

http://www.csgnetwork.com/fiflowcalc.html

And the 85 lb/hr injectors came on the later model TBI 454s (or are they 80s?).
How do you like that manifold? Was it worth the cost? What have you done about your EGR?

By the way, the computer is going to have to do a lot of learning to get back some of the proper drivability with those 85 lb/hr injectors, unless you custom program. I think you could get by with just sticking them in and setting the pressure at a figure that eventually gets you a BLM of 126 or so, but the WOT will always be compromised, as will the idle. It WILL work, just give it time to learn, I think (temporarily, before custom ECM work).

Audiman

I like the manifold alot and I think to keep the egr it is worth it. I ran a 96' chevy pickup manifold and crossover tube to make the egr work. You can get headers for it to that have the same egr tube hook up. check with www.paceparts.com and call them get a catalog the whole kit is in there for the vortec conversion. I already have a custom superchip to compensate for my cam and other components. Pace had it burned and if I disconnect the ecm I think it will be ok as far as relearning the intergrator curve. I will call mark to see if superchip will give me a new chip, they already have once.

super chevy

I would replace that Jet fuel pressure regulator with the vAFPR. Made a world of difference in driveability of my truck. Mine is set at 9psi idle and 16psi WOT. Truck is real snappy off the line, idles great, and no more leaning out at WOT.
The vAFPR is $41 from gmpartsdirect.com part #17113186. It's nearly a bolt on deal. SC

kevm14

You say nearly - I take it you had to replace the spring.

This sounds like what I will eventually need...something like 12psi idle (high vacuum) all the way to around 18 or 19 psi at WOT...

super chevy

Yeah, nearly. You have to change out the spring and run the vac line through your air cleaner to a manifold vac port. I also plumbed in the recommended vac delay valve from NAPA between the fpr and manifold vac source. No big deal. SC

Audiman

Dude, you guys have got to spell it out for me. What does it do, where does it hook up and how do you hook it up. I researched some old tech articles and so far I can tell you would need manifold vacuum (or Port?) hooked in to the vafpr. Put the new assembly where the stock or the jet one is and set base psi. What's this about changing the spring? Super Chevy do you have a vortec set-up? My truck is leaning out at wot. Is there is formula for what wot psi will be or is that what the spring is all about? Do you have to check psi under load or can you rev the engine at idle. I will get going on this as soon as you guys let me know, it sounds slick, just like the fuel pressure regulator on the mpfi setups. Will it work ok with cams too? :

kevm14

It sounds to me like it bolts on where our regulator currently sits, on top of the injector pod.
I mentioned changing the spring because that will give you a different base -> WOT pressure range, most likely moving it up and down, like a cam does to a torque curve.
What you'll want to do to set WOT pressure is just disconnect the vacuum line and use trial and error (unless someone knows something) to find the right spring for a good WOT pressure. The base pressure will likely fall into place as something the ECM can work with. Ideally, the base pressure will be 9-13psi, but mine is 15 and my car is fine with it. I bet you could get a pretty high WOT pressure with a 15psi base pressure...The only reason you'd have to check the pressure under load would be to diagnose a weak fuel pump. Otherwise, idling with the vacuum connected sets the base pressure and unplugging the line sets the WOT manifold vacuum (pressure will read slightly higher with the line unplugged, but you will be within 5% probably). Then go drive with a fuel pressure guage as the final step and make sure it has pressure where you think it needs it. After that, let the ECM learn the part throttle BLMs and whatnot...

super chevy

I followed what everyone else did with the vAFPR mod.
Here's a thread that discusses this mod in detail:

https://www.thirdgen.org/techbb2/sho...ighlight=vafpr

Audiman

I put on a new cat last week, huge difference in low end power. Edelbrock is going to be sending me their conversion chip. The fall off at 3500 I found out is the torque converter lockup.