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Converting EFI to carburator

752 views 3 replies 3 participants last post by  jseabolt 
#1 ·
I've got this "roached out" 1992 Nissan Sentra I've been trying to get running. I'll try to make this as short as possible:

Compression wet test: 185,190,210,195 lbs
#4 cylinder has spark and injector is firing.
40 PSI of fuel pressure

Engine appears to be flooding out.

Check engine light flashes a code 13 which indicates a bad coolant temp sensor which will definitely flood an engine out if it's not sending anykind of reading to the ECU. When checked with an ohms meter, the sensor shows an open circuit instead of around 1600 ohms at 80F (well based on a Bosch L-jet sensor). Replaced sensor and connector. Engine still appears to flood out.

Pumped the 2 year old gas out of tank and added 3 gallons of fresh gas.

Still nothing.

So I'm thinking about installing a side draft 38mm Zenith S&S carburetor from a Harley Davidson I have laying around in place of the throttle body. All I need to do is fabricate a 3.25" X 3.25" plate and mount the carburetor to it. That's the easy part.

Then reduce the fuel pressure down to about 3 lbs. But before doing that I'm going to gravity feed it just to make sure it works.

My biggest hurdle is how to link the factory throttle cable to the carburetor. Or even link the accelerator to the throttle even if this requires cutting it down so it pulls from the opposite direction and fabricating something to go on the end of it.

The throttle body looks like this:



Here is what the carb looks like except it has a ball socket connector. However this particular carb has a similar piece that might work with the throttle cable:





I'm just wondering if any of you guys have ever done something like this if you can post some photos of how you did it so maybe I can get some ideas.

If I can verify this carb is going to work, I can cut down the throttle cable and attach someone on the end that might work.
 
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#2 ·
really... the idea is to not go rube goldberg..

start by disconnecting the vacuum hose to the fuel pressure regulator.. have somebody cycle the key on a few times.. you may need to actually crank the engine.. the air flow meter may turn on the fuel pump on that.. i will have to check the wiring diagrams..

you should not have fuel coming out the vacuum fitting of the fuel pressure regulator..

do you have a proper wiring diagram for that engine's fuel injection system.. so you can ohm the individual circuits at the ECM connection with the ECM disconnected.. its not hard if you have a printer to print the connection diagram a few times and mark it up to which to test..

you may want to without touching the circuit board.. remove the computer and inspect it for cracked solder joints. damaged ones will seem to have 2 different shades of solder or just a ring in the solder showing.. i have to resolder ecms and pcm almost weekly. its not for the never done that before people.. you can screw it up really badly in seconds..
 
#4 ·
Thanks for the link Wayne.

I must point out this car is roached out. It has a hole the size of a basketball between the trunk and rear wheel well and the passenger door has issues shutting. The door jab has a large crack it in below the upper door hinge which I will weld up. Among parts of the wheel wells and rockers have large rust holes. The car has 207,000 miles on it. I'm surprised the compression readings were that high to be honest based on the over all condition of the car.







The car belongs to me now and I have a title for it. My wife wants me to get it running for her son. I'd like to just patch the car up because I don't think it's going to be on the road very long.. That's why I don't want to put allot of money in it.

I have some limited experience with fuel injection. Only the old Bosch L-jetronic systems with the O2 sensor. I have diagnosed some issues with my Subaru and Explorer like misfires and bad O2 sensors but that's about it.

The ohms on the spare Bosch coolant temperature sensor I tried from my stash of Fiat parts actually came close to what the link you posted (1600 ohms at ~ 80F) so the car should have started.

I did not think about the fuel pressure regulator causing the engine to flood out. While cranking the engine over, the fuel pressure gauge measured 40 PSI which sounds about right compared to my Bosch L-jetronic Fiat Spider. I wouldn't think it would flood out at that low a pressure.

The NODE tester I used on the #4 injector was somewhat suspicious. I know injectors pulse in milliseconds but seems to me the LED was more constant than a flash while cranking the engine over which leads me to wonder if the injector remained open instead of pulsing. But it maybe hard for the eye to see flashes in milliseconds. I would think the flash would be consistent with the spark plug flashing.

There is a purple sensor/connector on the end of the intake plenum. I think it's the cold start valve. I tested for power while cranking but never seen it flash. I have accidently forgot to plug the cold start valve up on my Fiat Spider before. It only opens below 95F by means of a temperature sensor in the intake manifold. Below that the car will start but takes maybe 3 or 4 seconds longer around 70F.

I'm sure this system is probably based off the Bosch system. The system was licensed by Bosch to Motorcraft on Ford 2.3 liter engines and Nippon Denso systems used on Nissan 240Zs among others.

With that said, I've already spent 20 hours if not more trying to get this car running. I'm thinking since I already have a carburetor, it's just a matter of getting the accelerator cable to link up to it. I actually converted a fuel injected Fiat Spider to dual carbs once because someone had monkeyed with the system to the point it was going to cost hundreds of dollars to get everything sorted out.

It turned out this Sentra needed new wheel bearings and or CV joints. The guy was a friend of my wife and I agreed to fix it. I thought he was going to drive it over to my house but instead had it dropped off with a rollback. He said the car would not start. For starters one of the cells in the battery busted and leaked acid. I don't know if they tried to jump start the car or not. Next thing I know here I am trying to get the car started.

I asked the PO if the car was running poorly before and he said he was driving the car and it got to where the fastest it would go was 30 mph at full throttle then eventually picked up power. Which sounds consistent of engine flooding. The plugs were also carbon fouled. So he drove it home and it sat for 4 months until he had it dropped off at my house.

I'm thinking the apartment owner told him to get the car off the premises and he needed a place to dump it.

If this car was in better condition, I would just take it to this guy I know and have him diagnosis it with his Nissan diagnostic system but like I said I already have $200 in this piece of junk and I'm just trying to patch it up.

I wish I had some spare parts like a mass air sensor and pressure regulator to try.
 
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