1997 3100 to 2005 3400(w/ ECU) in Monte Carlo

[rxkaffee]

Hi all, I've looked around in the forums, read the 3400 swap guide, and utilized a few other resources so... I hope that my post will not be too un-informed. However I am very inexperienced and unlearned in the topic of chevy 60degree engines and swapping them around.

Background: We have a 1997 model Monte Carlo that came originally equipped with a 3100 engine. The P.O.s had extremely poor maintenance practices, so we inherited a very gunky mess in just about everywhere that one could come up.

The engine recently gave out on us, and we have been considering a few options for getting our daily driver back on the road. Yes, Daily Driver. This swap is not to gain any performance, and I have no desire to gain any. We would like better gas mileage though, and for that reason have considered swapping to a 3800 Series II. However it is looking like the parts for this will be outside of budget.

I have found some sources of reasonably priced 3400 engines, from low-mileage 2005 chevy Equinox. As I understand it, there is an issue with using these engines because of a difference in the crank-position sensor.

Is it possible to use the ECU from the Equinox 3400? I am not familiar with how chevy seperates engine controll and auxiliary functions. I would imagine that the newer ECU's would have more efficient/more fine-grained controll over the injection system, leading to some better fuel economy. If able to use the newer ECU, this would also allow usage of the injectors and such from the Equinox. I'm sure the ones on our busted 3100 are in horrible condition.

If engine controll, and auxiliary functions are handled by the same box, would it be reasonable to run both ECUs? Connect only engine components to the 3400 Equinox ecu, and connect gauges, ABS, etc. to the 3100 Monte Carlo ECU?

If this setup is completely and totally a no-go, would it be possible to use a 3400 that doesn't have the odd crank sensor, with an ecu from a newer (2001-2004) Monte Carlo that came with a 3400?

[bszopi]

Besides the crank trigger in the Equinox 3400s, you also have to deal with their unique intake manifold, which will not fit under the hood of a Monte Carlo. BUT, if the price is right on the engine, you could always get a new upper intake as well as an external crank trigger and the engine would work fine with the existing PCM.

Newer vehicles (shall we say 2001+?) have a lot more crap in them when it comes to the computers and such. These newer vehicles have BCMs (body control module) that also interact with the PCM, so trying to install a newer PCM into an older vehicle, such as what you are looking into, becomes a major PITA.

Welcome to the site, by the way! Where are you located, as there may be a member local to you that could potentially help you out. Oh yeah, and stay away from the 3800, aka boat anchor, aka fire starter.

[jtwmechanic]

with most of the community here replacing their 3100's with the 3400-3500's i would think that somone here would sell you a good motor cheap! since you don't have a need for more power lol i would just put a 3100 back in it is a very dependable engine and good milage if maintained. the fuel milage related to the equinox would more be in the computer than the motor anyway. tuning is everything.

[rxkaffee]

Hmmm... yes I guess you're right about sticking with a 3100. The hopes was that I could use a newer ECU and gain some economy. The mechanic doing the swap found a 3100 from another monte carlo. Tranny, fuel injection, everything but the AC and PS pumps. Should be a good setup for replacing all the gunked up parts on the blown engine. Sounds like if we go with that engine, he'll be putting on all new seals/gaskets, everything except rings (80,000mi motor).

Is there any way to estimate the condition of the rings while the motors out?

[robertisaar]

leakdown test: unthread a spark plug, rotate that cylinder over to TDC, use a compressor to push 100PSI into the cylinder through the plug hole, then measure how long it takes for the pressure to drop...