While getting ready for my 3.4 swap, I had a guy on facebook post this about his 3.4


" I always had a over rich condition, tried 3 MAF sensors with no avail, fuel pressure held steady so it wasn't leaking injectors, vacuum was at 22 in. Hg. So it was not a vacuum leak, tried two 02 sensors, no difference. The ecm just didn't like the motor. It caused the idle to surge up n down, the mpgs were as bad as a v8, and I was going through a t5 also. It was just weird. Switched out to the v8 and no more problems lol"

Anybody else experienced anything like this?

 

If that's what he tried then obviously he didn't find the problem.

There's a few other items that can cause an overly rich condition, one of which can really cause over-fueling and that is the coolant temp sensor. These do fail occasionally and when they fail, they tend to fail open, which causes the ECM to believe that the engine is cold, very cold, down to -40*C, which dumps a LOT of fuel into the engine.

Don't let someone with poor diagnostic skills put doubt in your mind about a swap you want to do.

 

So in general, that's not a problem you see come up with the 3.4?

 

No, but I usually see more S-10 owners who swap complain about being to lean until they swap injectors. But you have to keep in mind that this is with un-tuned set-ups.

With any swap, if there's a problem with a rich or lean condition, don't blame it on the engine when there's been little to no tuning done. And by tuning, I mean adjusting the bin file in the ECM in addition to a proper selection of supporting parts.

 

This. My 3.4 ran rich because I never retuned the ECM for the difference.

 

Sounds like he used the 3.4l injectors with the stock '85 - '89 MAF ECM. That will cause it to run rich. To use the 3.4 injectors, at a minimum need to change the injector flow rate in the ECM's calibration.

Note that using a speed density ECM ('90 - '92) will be different.

RBob.

 

Dumb question. If the 2.8 injectors are too lean and the 3.4 are too rich, is there anything in between?

Is a retune just a matter of a new chip?

 

Pretty much. The 3.1 injectors were the same as the 3.4 IIRC.

You'd burn a new PROM and pop it in the ECM.

 

I regret nothing about it because i have more than twice the engine i did before....yes its fully built but i would do it again

 

I had my 3.4 running the stock 88 ECM and it ran rich too. I still got about 23-25mpg though lol. I never regretted it, just after 10 yrs it was time to do something different, so I went the V8 route.

 

Chiming in kinda late here, but yes. You've got to return the ECM if you're gonna do the 3.4L V6 swap in a MAF car.

I'm planning on grabbing an EPROM burner this spring and trying to nail down a baseline. This way I can burn copies for other 3.4L V6 swaps.

 

A retune isn't mandatory on a MAF car, but definitely recommended for max power or fuel economy.

 

I'm looking at some brand new 19lb injectors. Are those an appropriate choice for a 3.4? Better or worse than stock 3.4 injectors?

 

Stock 3.4s were 17lb/hr injectors and ran rich on a stock tune. Are you planning on getting the ECM tuned? I wouldn't go with those unless you plan on it, you won't see any performance gains by doing it, may even hurt performance.

 

u can baindaid it by using the stock smaller injectors and running a cheap adjustable fuel presure regulator spliced into the rubber return line , once its installed u can adjust the fuel presure up to get the fueling to a apoint were its close to good but not perfect

 

I found a set of 19lb injectors for a good price and thought that was the correct size. If they aren't, I'll just go with the stock 3.4 injectors.

When it's all together, I'll tune the ECM for the 17lb injectors