S10 with a 2.5 TBI - Upgrades ?

I am attempting to help a friend with a 1990 S10. It has the 2.5 inline four with TBI. He's running a blow through turbo setup and he needs more fuel under boost. I'm not that familiar with the TBI stuff so I thought I would ask - what are some options to flow more fuel with this setup ?

How is he controlling fuel pressure?

IIRC, if you just stick a boost bonnet on top of the TBI, the fuel pressure won't rise in relation to boost pressure, effectively reducing fuel flow as intake pressure goes up. I'd have to study a TBI FPR to be absolutely sure.

AN FMU could also be used, to raise fuel pressure beyond stock delta pressure. I have one that I'm not using that I would part with.

Other ways I've seen this done is with extra port injectors placed just above the TB, and switched on at a certain boost pressure. Some people have even gone as far as adding a second ECM to control just the secondary injectors, or modifying the code for an extra injector output.

Having more details on the set-up would help determine how to make it work.

Or you could change out the injectors he has to 4.3L, 5.0l, 5.7L or 7.4L TBI injectors. When he gets to 4.3L it will also have bigger throttle plates, then the 5.0L and 5.7L also have bigger throttle blades and the 7.4L has the biggest throttle blades.

I believe the 2.5 uses a single throttle plate.

He said TBI if it's a single TBI than all the injectors above will fitbut the throttle body wont.

I was hoping a larger injector from a bigger engine TBI would fit into his throttle but didn't pull his pressure hat off to see what it looks like. I doubt other injectors are bigger anyway - he has one injector feeding 2.5 liters, 2 injectors feeding 5.7 liters = 1 feeding 2.85 liters, that's not much bigger

Is the pressure regulator not built into the throttle body and trying to adjust fuel pressure relative to boost on the TBI ?

How many lbs of fuel pressure will the stock fuel pump provide? He says it's about 17# - me I don't know :confused:

I think he's needing a MPFI intake from a FWD car on there and a new puter

If it's the TB I'm thinking it is, it uses a different injector than the dual throttle plate truck TBs.

I'm not sure there were any MPFI intakes for the 2.5. I can only recall TBI applications, including the Fiero.

That being said, an intake could be converted, and MPFI will make getting proper fuel supply a lot easier.

Yes, the FPR should be part of the TB.

As far as the pump max pressure, they can vary, especially depending on age. Most people seem to say max TBI pump pressure is about 20 PSIG, but some say higher. The later 454s would run about 20 PSIG base pressure.

You really need to see what the fuel pressure is doing in boost. It should rise at a rate of at least 1:1 with boost pressure, if it doesn't then you are reducing the delta fuel pressure that will have less flow the higher the boost pressure rises.

Basically he is going so lean that the thing shuts down completely at 2500 RPM.
He is planning to go MPFI with it but I was hoping there would be an easy option with the TBI. Apparently not :sad:

Making an adapter to mount a 2 barrel TBI would probably be about as simple as he could go with that setup from the sounds of it
Thanks guys

It sounds like the fuel pressure is not rising. Like I said before an FMU might be the esiest option, at least for the time being.

If he's interested I have an adjustable one for sale.

The one barrels I have seen are the same as a two barrel and in jectors are interchangable. I think 17 PSI is max with out a new spring.

Just to see what it would do he blocked the return line on the fuel - to get max pressure - didn't help much at all. If the stock pumps only make 17-20 lbs there isn't going to be much more flow available even with the FMU maxing out the pressure is there ?

What if he switched to a regular multi port fuel injection pump that can make 70 lbs pressure and used that with the FMU ?

I'll have to grab the TBI that is in my GF's Mustang and take some pictures, most, if not all, the late model single TBIs were a different injector. The early single TB had a similar injector to the common dual throttle TB, but I believe that was last used in about '87 or '88.

No, with the pressure maxing out at 17 PSIG with the return line blocked won't benefit from the FMU at that point.

Possibly using an MPFI pump might get what you need. I'm just not sure how well it will work at lower pressure.

I do know a guy that uses ford MPFI pumps in TBI applications without issue.

I've run 18 PSI no issues on a TPI pump. Now that is an external TPI pump from NAPA PN#5000 or PN#5001 i get the 2 mixed up, one is TBI and one is TPI. The TPI is cheaper for some reason but the pumps look identical.