90-93 engine in a 94 Q45a

[dsagers]

A while ago I bought a beautiful 1994 Q45a from QSIGUY

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After researching the forum messages for a couple of months, I decided that using a 90-93 engine in the car was doable with the info available.

Anyway, may I ask for your help?

Here is my situation, when you have a minute see if you have any thoughts or advice.

With the 90-93 engine and harness installed in the 94 car I had the engine running last fall just before the weather turned cold. It started and idled just fine, but I never drove the car. In addition to a lot of small things to tie up, such as the radiator, brakes and AC, I thought there were only two issues to solve.

One, the fuel pump in the 94 would not run off the 90-93 ECU and harness, I had to jump the fuel pump in the trunk.

Second, the 94 car side harness has a brown plug under the dash above the ECU. There is no matching plug on the 90-93 harness or ECU. I figure this brown plug has something to do with the fuel pump, and possibly the AC and instrument cluster, but I'm just guessing here.

I paid a guy to modify a 94 harness to work on the 90-93 engine, but that turned out to be an expensive mistake.

So here are some questions I could use some advice on.

I have both a 90-93 harness and a 94 harness. But the 90-93 engine has an EGR set up that looks different than the 94. I figure the car will run better with a working EGR system as I have a great deal of confidence in the engineering of Nissan vs what I can speculate on. So I'm in no hurry to just skip the EGR. Would you use the 90-93 or 94 harness and modify it to work? Why?

Next, will the 94 TCU work with a 90-93 ECU? I figure since the "NICO" modified ECUs are going in 94 cars, and all modified NICO ECUs are 90-93, this should not be a problem?

Finally, the brown plug under the 94 dash, what all does it connect to?

Thanks


Modified by dsagers at 2:15 PM 5/7/2009

[goody90q45]

......But the 90-93 engine has an EGR set up that looks different than the 94. I figure the car will run better with a working EGR system as I have a great deal of confidence in the engineering of Nissan vs what I can speculate on. So I'm in no hurry to just skip the EGR. Would you use the 90-93 or 94 harness and modify it to work? Why?.....

I compared the EGR systems on my 90 and 94 and other than the mounting location of the 2 sensors and the routing of the vac tubing they appear to operate the same. The big difference is the 94's EGR hoses dive under the plenum via a group of small diameter metal tubes and the 90's system is plumbed using mostly rubber tubing. You can set the 92 engine up to use the 94 components by swapping in the tubing manifold from under the plenum.

will the 94 TCU work with a 90-93 ECU? I figure since the "NICO" modified ECUs are going in 94 cars, and all modified NICO ECUs are 90-93, this should not be a problem?

A 94 TCU is not the best match but it will work. IIRC one of the cooling fans does not operate but it doesn't seem to be a problem.

.....the brown plug under the 94 dash, what all does it connect to?

I compared FSM's last night until I had a headache and couldn't figure it out. Earlier in the day I was finally able to locate the brown plug on the 94 mounted under the white plastic block directly behind the ECU but was unable to figure out (visually or with the FSM) where it routes to. Gosh my ribs hurt.

[dsagers]

Thanks Mike, I'm getting closer!