Dakota 3.9L V-6 Intake Manifolds and Use of EGR

[biggman100]

As many of you already know, i have a 1994 Dakota, 3.9, 5 speed. Recently, found some major issues with the engine, so, i found a complete, good running 3.9 from a 1998 Dakota. Today, i went to swap my intake to the new engine, and, due to using the cork end gaskets, which i have since found out i wasn't supposed to, due to them being too thick, i snapped the intake in half when i went to torque it. My engine has EGR, but, the new engine doesn't, so, my question is, since everything else is the exact same on both intakes, can i use the non-EGR intake from the 98 on my 94? I know it may throw a code for the EGR not being present, but, other than that, what other issues may arise from eliminating the EGR system? The biggest reason for this is, finding an EGR intake wont be easy around here, as most of the yards are getting away from older vehicles. My biggest concerns are that i have some very long, 400 mile or more, round trips coming up, and, each of those trips will be towing a vehicle at least half way, and, i don't want to cause any damage to the new engine, and waste all the work i did.

[Moses Ludel]

biggman100...What I like about your posts is your candor and straightforward approach.  Yes, you screwed up, so move on with that lesson and get it right with the next move...

The EGR is important and often dismissed as just a pesky emission device.  The purpose of EGR is to reduce NOx, which is caused by upper cylinder heat.  An EGR valve dilutes the incoming air/fuel charge with exhaust gases, and in the process, the combustion process cools.  The target is 2500-degrees F or less to reduce NOx emissions.

When I earned my California smog inspection and installer license in the mid-'eighties, there was much discussion about the EGR valves on carbureted and newer EFI engines.  I attended a NAPA seminar on emissions, and the instructor noted that upper cylinder temperatures can reach as high as 4,800 degrees F without EGR.  This is especially true with lower octane fuels, which are quite volatile and burn quickly across the piston crown.  6,000 degrees F will readily melt metal.

From that point on, I viewed the EGR valve as a passive (non-power robbing) device that could protect the engine from upper cylinder overheat.  Even on performance engine builds for magazine project vehicles (OFF-ROAD Magazine in particular, I built two 383 Chevy small-block V-8 stroker engines for Land Cruiser FJ40s), an EGR manifold and EGR valve was my choice.  This provided insurance against excessive upper engine heat and risk of detonation.  

Note:  I could run low octane fuel in any of my engine builds.  For all-around use both on- and off-pavement, my typical multipurpose engine build was 8.7:1 compression with a CompCams 252 grind camshaft.  These engines ran well with 87-88 octane fuel, no ping/detonation and no risk of pre-ignition.  Ignition timing on conventional distributors was adjusted according to fuel type.  From 1991-on, I ran the J&S Electronics SafeGuard device to control timing with its knock sensor trigger signal.  This brilliant device constantly adjusts individual cylinder spark timing while the distributor rotor spins.

If the '94 Dakota 3.9L V-6 engine uses a knock sensor, eliminating the EGR could create a power loss by retarding the timing to compensate for an increase in knock.  The engine would be prone to knock without the EGR, and the knock sensor would tell the PCM/ECU to retard the spark timing.  The result:  Loss of power.

I would find an EGR manifold and restore the system to OEM design.  In any case, the EGR is a win, it has very little if any performance impact and has much positive to offer!

Moses

  

Edited February 8, 2016 by Moses Ludel