SloNlo350

I just finished my TBI to TPI swap on my truck, but it stumbles really bad with any throttle input whatsoever. Its also really stubborn on startup. It usually takes about 2-3 tries to get it to fire and then one more try after that to keep it running. Even when it is warm it might take 2-3 tries to get it going. Now I knew it wouldn't be perferct cause I got screwed on the injectors. I was told they were the 22 pph, however after checking the numbers the were 19 pounders. So I got an AFPR to TRY and compensate a little, but my fuel pressure gauge stopped working today . So I am just blindly increasing fuel pressure until TTS Datamaster reads decent on the fuel table histogram guy. Every cell that had registered something was green (lean). Would a really lean mixture make it hard to start and seem like it is going to shut off while cruising at part throttle? I gotta get her running right by monday because I am NOT taking my dad's truck back to FSU again.

I'd appreciate any input.
Thanks,
Chase

bobsroc

Nice truck
I would go get a fuel gauge ASAP, even if it is a test gauge, connect it the the fuel rail testing point, set your fuel pressure to 50-55 with vacuum line off and plugged, truck running at idle. Connect to vacuum back up, start truck, fuel pressure should drop 10 PSI from your first setting 40-45. That should get you in the ball park. I would then check your basic tuning stuff like TPS, minimum air flow, idle speed, timing. All of that will effect throttle responce on a TPI motor. I am assuming you have good plugs, cap, rotor, wires, air filters, etc.

SloNlo350

Ok, it seems that I can't get the pressure above about 37 psi when it is running, and the pump doesn't stay on long enough to check it when i just turn the key. Also, when i disconnect the vacuum line nothing happens... pressure remains constant, but when I rap on the throttle a little it does drop so I know it is getting a good reading (or appears to be anyway). I replaced the filter, and all the sensors look alright through the computer. Timing is good, and the ignition stuff I would assume is good because it all worked fine before the swap. The last thing i can think is the pump... which is BRAND NEW. I just put a TPI pump from JimsPerformance.com, but that is my last option... either that or there is something up by the rails that has a problem, but I don't know how that could do it. There are no leaks (that I can see anyway).

bobsroc

Will that fuel pump push 50+PSI, your injectors need that kind of pressure at WOT. I am curious why your fuel pressure doesn't go up and stay steady before your turn the to the run position. Your pump should be wired to run in the run position, without motor started. Hope your still online, post me back

SloNlo350

ah, sorry, i went out and fiddled with it some more and got nowhere so I just cleaned up and went over to this girls houde (REALLY needed to unwind). Anyway, see, with the TBI before the pump ran like that, and the new TPI pump (GM # 25116163) runs just the same way. When I turn it to run it goes for about 5 seconds and then cuts off. Then when I turn the key off it won't start again until I let it sit completely off for about 10-15 seconds. I thought it was supposed to work like that since the TBI did that. BTW My truck is a '95 and the TPI and computer and all is from a '91 305 Camaro. I have a 350 PROM though with VATS, Speed limiter and EGR removed. What could be causing it to shut off? If there is something off in the wiring that might be causing it to not mae adequate pressure and it just cannot produce more than that 37psi. This has me a little worried now... i dont wanna take te bed off again!! Looks like I'll have 'til tuesday to figure it out with this hurricane that just decided to take a turn towards me (and is scheduled to make langfall Monday afternoon... when I was planning on going back to Tallahassee... so no class for me on Tuesday )

Thanks for trying to get me straightend out here. I'll look for more information about this pump deal.

rgarcia63

[QUOTE]Originally posted by SloNlo350
[B]... When I turn it to run it goes for about 5 seconds and then cuts off. Then when I turn the key off it won't start again until I let it sit completely off for about 10-15 seconds. I thought it was supposed to work like that since the TBI did that... [/i][b]

That is normal:
That's enough time for the fuel pump to pressurize the system, and the pressure should hold, (sometimes for days.) if it doesn't then there's a leak some where, or the pump's check valve is failing. If you don't think the pressure holds long enough for you to get a proper reading (40.5-47psi @ idle 30.5-44psi for 1985-1990 v8s except corvette and DOHC) then turn the key off and apply 12 volts to the ALDL connector's "G" terminal to power the pump continuously. Remember this is for the ALDL connector for 85'-90' models please verify yours is the same.

bobsroc

Remember this:TBI needs about half the fuel pressure as TPI. Make sure your pump is rated for TPI use, 60plus would be my recomendation, I have seen PSI numbers to 60+PSI to atomize fuel for some setups. With hopped up motors and bigger injectors, you are going to need that much pressure a WOT to deliver fuel. 37 PSI isn't enough to work the injector at idle, let alone WOT. You need to work this out before moving on. As far as the pressure not staying up after your key is in the run position, thats not good either, the system should pressurize and hold above 50-60 PSI at the fuel rail test port. As stated earlier, the system should have a check valve in the return fuel line that will keep the fuel pressure to 50-60PSI always. Your fuel lines should be 3/8" I believe, both sides, feed and return. Check the fuel filter, look for leaks, get 50+PSI on the rail before you start tweaking anything else.

406-IROC

My GTA (once upon a time) had a similar problem, and would never throw out any codes explaining why. Believe it or not, it turned out to be the Fuel Pump Primer switch... in which the ECM was not receiving it's 'oil pressure' signal, causing it to cut the feed to the intank pump (about 3-5 seconds after start up).

SloNlo350

So there is this little stretch of tube between the pump outlet and feed line. Well aparently the one that is on the TBI pump won't stand up to 60+ PSI of pressure... and leaks... at I'd assume 37psi. I replaced it with a similar length of harder rubber fuel injection line and now it runs 99.5%. I still get a little hickup once in a while. It happened 3 times over about a 45 minute ride through town, and once it was REALLY low on gas, so i think the fuel just ran away from the pump, which tends to happen below about an 1/8th of a tank. So I rode around and saw some friends and showed it off. I am SO excited. I'll get me some new injectors and a cam actually meant for fuel injection and then some better heads (have a line on a set of ported and completely polished, inside AND out Aluminum L98's). And then some TPI mods, and maybe she might get halfway decent on the track... maybe so i wont embarass myself at least.

bobsroc

Congrats, glad you fixed it. Surges can be caused by the TPS sensor on the throttle body, might see if you have a flat spot on it.

SloNlo350

alright. i'm just glad its going right now. It is still a little stuborn on startup. not nearly as bad as before, but it is a bit annoying. It takes too long for my remote start. I think maybe i just need to up the fuel pressure a bit. It is about 60 when off and high 40's-50 when running and as I said in my first post I got screwed with the 19pounders so I think I just need to turn that up a bit. Also I have my timing set at 0 so I'll crank it up just a tad and see how it likes it. Plus I think I still have a vacuum leak somewhere because it idles pretty rough and then there is the start problem. But it IS totally drivable right now. I've been all over town showing it off.

bobsroc

Rock on!! Sounds like you have a handle on it, set your fuel pressure with the vacuum off, idling, my 19lbs like 50. With vac on fuel pressure at idle will drop 10 PSI, assuming your vacuum doesn't have leaks? As you stated, set timing, minimum air, TPS. You should be golden.

vortec77

why didnt u go with 22lbs injectors? 305 engines have 19lbs and 350's have 22lbs u said u have a 350 right?

vortec77

Also are u running a tpi with a cold start injector or no?, 85-88 had the cold start injector set up.

bobsroc

Check the tech note off this sites main page for the details on setting minimum air control.

SloNlo350

I have 19's because i was told it was from a 350. I wouldnt have even known except when I had my harness reworked i had to send my ECM along also and the guy said, "You said you have a 350 right? Well that chip you have is for a 305." So then I got the numbers off of my injectors and sure enough, 19's. I will take the guy's word for it that I bought if from that he honestly thought it was for a 350 because he is a friend of mine, and he was going to put it on a 350 until he got an LT1. So I decided I would just suck it up and live with them until I can sell some stuff and get some 22's.

And it is all from a 92, so no cold start injector. I got it running good now. Set the timing and fuel pressure... but about this minimum air deal. I haven't heard about that yet. I did see something about that while watching TTS datamaster. TPS is fine and it idles good now, just that darn hiccup every once in a while. And it is still difficult to start. The hiccup seems to happen only when I finish accelerating from a red light or whatnot at about 45-50mph right after I level off. It is just a little annoying, and doesn't do it but maybe 3-4 over the course of an hour.

SloNlo350

Nevermind about that ^... If I'll dare to venture out of my own thread I would see the other guy having EXACTLY this problem. I'll go check the TPS now

EDIT:

Alright, jsut checked the TPS, and it is .57v closed and 4.22v at WOT. And it is smooth all the way through, and it only does it (as in the other gentleman's thread) cruising in OD at about 45-50 mph (1200-1500 rpm). I'm glad its happening to someone who's car actually came with the TPI though, so I know I didn't screw something up on the install