4.5 ECM Req'd for Original 4.1 Car?
 

Hi, I have an '86 Eldorado which has been "upgraded" to a 4.5 TBI motor from the stock 4.1. Everything from the air cleaner thru the intake was retained from the 4.1. The issue I am having is an erratic idle--it varies from 550 to 800, and the car idles very poorly as a result. I have tinkered with the idle control motor, TPS sensor, etc, and paid a mechanic with 30 years of experience to do the same. His conclusion was that the fuel injector pulses were different between the 4.1 and 4.5 motors, which causes the idle issues, but more-or-less goes away while driving. He wasn’t sure that replacing the ECM would solve the issue.

So that is my question—do you think that replacing the ECM with one from say, an ’88 Eldo will solve the idle issue? Will it create others? Thanks for any words of wisdom!

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

You dont need computer, but you need custom PROM. I suggest to search web, it seems someone should make them.

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

A couple years ago we replaced an '87 Allante' 4.1 with a '92Allante' 4.5. There were no driveability issues whatsoever, and no trouble codes once we got through. We reused all the emissions equipment and modules off the 4.1. This included the air pump, EGR valve,AIR valve, exhaust manifolds, EGR pipe,O2 sensors, upper intake, etc. We retained the original transaxle. The car ran and idled perfectly. There arevery significantdifferences in the emissions system between those two years. The '92 had no EGR valve and no pump and no AIR valve.I would suspect there is something different somewhere in the emissions system that could be causing your problem.

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

The allante used it's own unique pfi system. The 4.5 & 4.1 TBI engines fuel requirements are very different.

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

Thanks for the ideas. The car does not set any trouble codes. I kept thinking that it had to be an issue with having the TPS voltage properly adjusted, and/or the idler motor. But it does seem to be a fuel issue of sorts. Is the PROM a chip within the ECM? If so, would replacing it with a 4.5 PROM chip fix the problem, or would I need a customer chip b/c the sensors etc. are still from the 4.1 motor?

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

4.5 has different intake manifold and tbi (larger). In 88 faster computer came out,I dont believe the 88/89 chip will work in the slower computer.

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

slowroll,

what do you think would happen by using a NON-Allante 4500, lets say a Seville on a Allante with an
original 4100, assuming one uses al the 4100 emissions equipment and modules, including air pump, EGR valve,
AIR valve, exhaust manifolds, EGR pipe,O2 sensors, upper intake, etc. and retaining the original transaxle?

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

I would be surprised you want to go away from the allante long ram intake. Trying to run TBI won't work with out major investment. I would be more interested to put in 4.9 with allante 4.5 intake re-using 4.9 injectors.. Not sure 4.1 intake will work on 4.9. The Allante was the test bed for many of the things to come, and due to low production emission waiver would have been possible and the computer more able to compensate for changes.

RE: 4.5 ECM Req'd for Original 4.1 Car?
 

Slowroll, thanks for your help. Is there a way to verify that the 88/89 chip won't work in an 86 ECM? Just want to be sure b/f I shell out several hundred bucks for a custom chip.