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From 368 EFI to Q-jet

10K views 28 replies 4 participants last post by  Cerbera 
#1 ·
OK guys, here’s my question
Will a Q-jet carb (M4ME) bolt on directly on my current EFI intake manifold?
My reason for his question? Allow me to explain :)

My car (83 Seville with 80 368 EFI engine) runs primarily on LPG (Liquified Petroleum Gas)
This is mainly done in The Netherlands for financial reasons. Because unleaded fuel runs about 9 dollars per gallon and with a fuel consumption of 15 mpg or way less, not funny.
However our goverment needs money and decided to tax all classic cars running on diesel or LPG between the age of 39 and 25 years old.
In turn this means that a lot (American) classic cars need to converted back to run on unleaded again to avoid this tax. Otherwise I’m looking at 3000 USD a year in road tax. Once again, that’s not funny.

Now I know there’s more in converting the car from EFI to a carb than just that, so if there any tips on that too it would be highly appreciated.
Already thought of fuel pump btw.....
 
#2 ·
You will need a manifold to go with that carb and a different engine wiring harness. I am sure the manifolds for the 368 engine are different and not a good interchange with the 425/472/500 engines. If the engine has been converted, perhaps these parts are available in Europe.
 
#3 ·
Is your EFI set up the stock Cadillac TBI system? If yes, just run it with regular gas, that's what it's designed for. However, I suspect that the LPG conversion is not the GM TBI set up. Take the air cleaner off, and take us some good pics, we'll be able to help you. It either already has an intake that will accept a Q jet, or, it has the EFI intake that will take the two barrel TBI set up.
 
#4 · (Edited)
Hello Jay,

Yes the stock TBI system is in place. The LPG conversion just bypasses it. I will run it on regular gas because I know it can take it.
Unfortunately I forgot to mention that the previous owner (or the one before that) had the LPG installed but the installer cut some wires and sensors so thats why I have to convert to a carb.
I will take some pictures as soon as possible.
 
#6 · (Edited)
Sure would be cheaper building it back together, but would it be possible? thats the big question for me for now anyway.
Anyway here are some pictures
general view

connector idle motor cut through

MAT sensor I'm not mistaken

original TBI as you can see

not quite sure what this is?

EGR blocked off

not quite sure what this one is but its ok

whats this one by the way?
 
#8 · (Edited)
It seems your right on the manifold issue, I did some calling around and the 80 EFI manifold does not take the Q-jet carb. Unless you have the manifold of 80's Fleetwood or Deville.
However I'm curious about the wiring harness. Why wouldnt the harness be ok for the Q-jet?
MY car runs on LPG and all the functions on my (digital) dash are working
 
#11 ·
The wiring for the 4100 should be very similar to the TBI 368. I can see in your pics that the engine is not the 81 8-6-4, so I'm thinking that they just used the 4100 wiring. Might want to pull the computer out from under the dash to see if it is the 83 4100, or something else.
 
#12 ·
Welcome and good luck Cerbera!
Are you in contact with the Cadillac Club Netherlands? They have some gear heads that might be able to help you out on site too.
 
#13 · (Edited)
@jayoldschool

I heard the same thing about the wiring for the 368 and the 4100 but wasnt sure this was true.
Will check the computer as soon as possible so I can be sure which computer it is. And also check if it still has the MAP and Baro sensors as well.

What do you think of the wiring itself? worth to give a try and order some parts at Rockauto?
As far I can see I would need a MAT sensor, ISC connector, MAP sensor (if its not there) and possibly a new ECU (if its the wrong one)

Concerning the Q-jet, I took a look in the service information manual and it also has an idle speed solenoid so it would need a signal from the ECU as well somehow.

By the way, I did manage to find a Q-jet here amazingly, for a price of course

----------

@70eldo
Well not yet actually, will do as well.
can use the luck thats for sure:)
 
#15 ·
Ok thanks, sounds logical. That solenoid wouldnt be necessary at the moment as my A/C still has the old R12 refrigerant in it and I need to convert it anyway but thats for later....

1:I found out that it has a remanufactered ECM still in place (1226930) unfortunately.
2:I've checked if I could find the MAP and Baro sensor but it seems to me their not there? see pictures below
Unless I'm not seeing what i'm supposed to see.

 
#16 ·
I'm going to look at 8-6-4 Sedan de Ville tomorrow to see if I can use some spare parts of that.
That would be nice, thats for sure.
I take it that the temp sense, map or Baro sensor wouldnt be that much different from a Seville.
Also, does anybody know where or who might have an eprom for a 80 Seville 864?
 
#18 ·
Ah. I see...No idea why I wrote that but I meant just an eprom for the normal 368.
I was looking for the baro, map, temp sense etc and some other stuff.
Not that he had any unfortunately.
I also saw that the Rockauto had the ECM but does it come with the corresponding eprom?
Just sent an email to ask if they know.
 
#19 ·
Does anybody have a list of breakers I can contact perhaps to find a manifold?
I have tried Cadillac King and Cadillacs only but until now i have received no response from them at all.
The situation is getting slightly critical as I'm expecting my first road tax bill of around 600 USD at the end of the month....ouch

Edit: all the ECU's I found are all without the eprom so thats a bit of a dead end as well.....
 
#20 ·
In worst case scenario you need to sign off the car (afmelden). But I am sure you already know that.
Did you contact the Cadillac Club for advise meanwhile?
 
#21 ·
No I havent contacted them yet but there is some progress.
I posted an ad on our national marketplace and apparently there's one guy who has both the ECU and the inlet manifold, how about that?
So I bought them both and hopefully they arrive some time this week.
Now i just need to fiigure where to start with what, ECU first and see if it runs or start immediately with the transformation to Q-jet?
We'll see.....
 
#22 ·
Well, in short I can say that I have been conned...
The guy is a total fraud after I ran his name through Google. Of course I should have done this earlier as the chance of someone of having both the ECU and manifold is rather slim.
But in the meantime I have decided to go with a stand alone system. I did some maths on trying to keep both of my cars but that just not possible.
It also helps that our city council has a cash for clunkers program going so at least I can partly pay for the system by bringing the car to the junkyard.
 
#23 ·
That really sucks! Sorry to hear that!
I didn't know the cash for clunkers is still active in NL?
 
#25 · (Edited)
Well back to the drawing board it is
The guy who was supposed to do the installation of the stand alone system has backed out stating the cars wiring was to much of a mess and was not sure what would happen with the dash as well.
Also he could not do it for the price we agreed upon as well.

So, back searching for a manifold and a carb
 
#26 ·
Any luck with Koen from the CCN?
 
#27 ·
Well had a breakthrough yesterday
sent an email to the guys of 500cid.com to see if a aftermarket edelbrock would fit (it doesnt)
but they do have a inlet manifold available for a 368.
Of course I'm pretty happy right now and I ordered a Qjet to go along with it as well.
 
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