PFF - Pennock's Fiero Forum, PDA Edition

WHICH FUEL INJECTORS TO USE WITH A 2.8 TO 3.4 CONVERSION (Page 2/4)

Raydar

DEC 01, 01:48 PM

quote

Originally posted by eti engineer:
... I am using RWD 3.4.
I received it yesterday and the first things I checked were tranny match up, starter location, valve cover fit, etc. It's all good. Thanks for the warning...

Whew! Excellent!
My apologies for missing your update / additional info.

I had 19# Bosch pintle-type injectors in my 3.4. (They were sold as replacements for a 98 Jeep 4.0 straight six.)
Using a stock tune, IIRC, it ran rich until it went into closed loop, and then it passed a sniffer test just fine. (Georgia used to do a 2 speed dyno-roller test.) Even with a 272 cam, headers, big throttle body, etc.

But yeah... 17s would have been better.

EDIT -

quote

Originally posted by eti engineer:
...
I think the 15 lb. units might have a tendency to be too lean. So I guess I will take my chances and order a whole new set of 17 lb. units and install them. I would think that if an engine is run too lean, it could also create emission issues, so I will go with the happy medium.

The real trick is finding 17# pintle-type injectors. The Fiero ECM is tuned for those characteristics. (Fierofool might have a line on those. I haven't talked with him about injectors in quite some time.)

BillS

DEC 01, 04:55 PM

quote

Very odd. I ran a 1985 ECM in my turbo Fiero as it is the only one that has the software for positive pressure operation and it ran my 17 lb injectors just fine.

In any case, for a 3.4 in a Fiero the stock 17 lb 3.4 injectors are appropriate.

Blacktree

DEC 01, 09:17 PM

As with many things, the answer is "it depends". The required injector size will be dictated by the engine's power output. A good rule of thumb for 60-degree V6 engines (running on pump gas) is 1 lb/hr for every 10 HP. So if you think the engine will only make 150 HP, then 15 lb/hr injectors will probably work. But the 3.4 V6 was rated for 160 HP from the factory. So for a stock 3.4 (iron head), 16 or 17 lb injectors would be ideal.

eti engineer

DEC 02, 10:02 AM

quote

Originally posted by Blacktree:

As with many things, the answer is "it depends". The required injector size will be dictated by the engine's power output. A good rule of thumb for 60-degree V6 engines (running on pump gas) is 1 lb/hr for every 10 HP. So if you think the engine will only make 150 HP, then 15 lb/hr injectors will probably work. But the 3.4 V6 was rated for 160 HP from the factory. So for a stock 3.4 (iron head), 16 or 17 lb injectors would be ideal.

The engine will be making a little over 200 hp, according to the builders. So you're saying I might have to go even larger, right?

Blacktree

DEC 02, 12:21 PM

If it's actually producing that much power, then yeah. Then you'll probably need 21 lb/hr injectors.

Here's a nifty injector calculator, if you want to play around with some numbers: https://www.rcfuelinjection.com/technical
Scroll down to the Fuel Injector Worksheet at the bottom.

pmbrunelle

DEC 02, 12:51 PM

The folks talking about lean/rich, pintle/disc, it's because they're trying to adapt the injector to the stock Fiero tune... If they get it close enough, then they can save the cost/time/headache of figuring how to modify the tune in the ECM.

In an ideal world, you select an injector to suit the engine (not the computer), and then you program the injector characteristics into the ECM.

For a 200 hp build, this sounds somewhat different from stock, so the engine builder should expect to modify the tune of your ECM.

Since the builder/tuner has to modify the tune for the modified engine's characteristics, it wouldn't be much more difficult to also adjust the tune for your injector characteristics, while he's in there.

Therefore, when you choose an injector, I would not add the constraint of matching the injector characteristics contained within the stock tune of the Fiero ECM.

[This message has been edited by pmbrunelle (edited 12-02-2020).]

Blacktree

DEC 02, 01:05 PM

I agree with the above. Your engine is producing almost 1.5x the power of the stock V6. So it's going to need a custom tune. You could have the tuner build the tune with emissions compliance in mind.

La fiera

DEC 02, 07:18 PM

quote

Originally posted by eti engineer:

The engine will be making a little over 200 hp, according to the builders.

A lot of builders get their hopes hi because they are used to build Chevys and Fords V8s, not knowin the 60* V6 is a different specie.
What's your set up? Cam, intake, exhaust, etc. Based on my experience I can give you and idea on what size injectors you may need.

Best wishes!

eti engineer

DEC 04, 10:11 PM

quote

Originally posted by cvxjet:

I have been running my 3.4 conversion (In a 85) for 20 years...It has passed smog 8 times and I am using the original injectors because the 17 lb F-body injectors would not work with my computer- supposedly the 88 computer will run them.

The only problem I have is that at low throttle movements (Driving in 25 zones) it will jerk back and forth a bit...Driven hard it runs like a raped-ape. I now have an 88 computer but it has no cold idle- it runs at 1000 rpm cold or hot.....I will try swapping in those 17 lb injectors in the future

Thanks for the information... This is kind of what I expected. I have ordered a new set of 17 lb. injectors anyway, as I was not planning on using the old ones. I will see how it works out, once I get the vehicle back on the road.

------------------
1988 Fiero, 1962 CJ-5 and more to come...

Notorio

DEC 06, 12:16 AM

quote

Originally posted by Blacktree:

I agree with the above. Your engine is producing almost 1.5x the power of the stock V6. So it's going to need a custom tune. You could have the tuner build the tune with emissions compliance in mind.

Can you really do that in CA? Won't the smog test equipment know that the engine tune is not stock??