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It can be done. I havn't done it, but am investigating the job too. I think any 151 from '79 & up is same and you would only to change the parts which bolt on the outside og the engine. '78 and down have different internal parts, but you shouldn't need to worry about that if your engine is OE. You could find a running TBI 151 engine from any Pontiac.
do some web searches on Iron Duke and/or pontiac 151. There are a couple of parts suppliers which specialize in the 151, more geared to drag racing... but still useful. Also Pontiac Motorsport has products available for the 151.



 
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Discussion Starter · #4 ·
Checked out some fiero's at the junk yard today. There is an early tbi set up and a later model set up. They look fairly different. I think the later model, 86 and newer, looks like it will work better. I have to do some more comparisons to my jeep 4 cyl. It looks like it can be done but just have to know what parts are needed and for me, if it will pass California smog.

 

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I read your profile to see that you have an 81 Jeep Scrambler. I'm thinking your 81 Scrambler will have the GM version 151. I know that Jeep started using it's own 2.5 liter 4 cylinder engine in the early 80's, which would not be very easy to convert to a GM TBI. I've also read some of the website information posted for the GM 151 engine. I know from personal experience there are several versions of the GM 151. I am wondering if it would be better to use a TBI system from a S-10 pickup instead of a Fireo. To the best of my knowledge the basic GM 151 TBI system had only a few changes, usually to the ignition system and distributors. I'm thinking that the Fireo and S-10 had different versions of the GM 151. I've seen the heads and intake manifolds are not identical in the different versions of the GM 151. It's been my understanding that Jeep used the left over short block assemblies of the late 70's GM 151's and the newer crossflow heads. The GM 151's used in the early 80's GM vehicles do not have the same bellhousing bolt pattern as the Jeep/GM 151's used in Jeep vehicles of the early 80's. For the most part, I think a Jeep/GM 151 of the early 80's would be easy to adapt to TBI. I think it might be worth a few moments of research to make sure the TBI intake manifold of a Fiero will fit on the Jeep/GM 151 head.
dave

 
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Discussion Starter · #7 ·
Didn't think of the S-10. What other truck/cars used the GM 151 in the early 80's? My scrambler does have the GM 151. It sounds like it might be fairly easy but there are always the little things that one doesn't think of. I assume not only would I need the TBI but also the intake, air cleaner, associated sensors and smogg stuff, and the computer if there is one. I'll have to take a close look at the ignitions also since like you say they probably are different being that the ignition is probably somehow tied into the TBI system on the S-10. Too bad we haven't heard from someone who has done this or maybe someone who can park a Jeep GM 151 and S-10 GM 151 side by side and compare.

 
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Discussion Starter · #8 ·
This might help you out a little the 151 and the jeep 2.5 were not used at the same time, it's easy to tell them apart the 151 has the exhaust and intake on opposite sides of the motor the Jeep 2.5 has the exhaust and intake both on the same side of the motor.

 
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Discussion Starter · #9 ·
I knew that part. I'm wondering about the details like electrical, sensonrs, ignition, etc. I suppose I should take some digital pictures of the motor in my jeep and go to the wrecking yard and do some comparisons.

 

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I have some additional information about a fuel injection swap for Jeep with a GM 151. Provided you find a correct match with the TBI intake manifold, the electrical stuff will bolt to the older GM 151.

Now let me describe some of the basic things needed to convert to a TBI. The TBI Engine Control Module (ECM) controls both engine timing spark advance and the fuel injector. The oxygen (O2) sensor is used to tell the computer if the engine is running rich or lean. So an exhaust manifold or the exhaust pipe near the exhaust manifold will need to have an O2 sensor. Most GM engines with TBI have an external ignition coil outside the distributor cap, and the TBI distributors do not a vacuum advance. Most TBI distributors have an ignition module with 7 pins, some TBI distribtors have an ignition module with 8 pins. Make sure the TBI computer, wiring harness and ignition system are kept a complete set. The computer wiring harness is usually cut in several places at most junk yards, so it's almost impossible to mix and match computers, wiring harnesses and ignition systems a make a mix match of TBI parts work.

The fuel pump for a TBI needs to have a fuel pressure of about 12 PSI, most carburetor engines have fuel pumps of about 4 - 6 PSI. TBI system needs a fuel return line to the gas tank. It's easy to install an electric fuel pump near the gas tank that can supply the correct fuel pressure for a TBI. The only problem I know of on the fuel lines for a Jeep would be the roll over valve on the charcoal canister vapor line. Sometimes it's possible to convert the charcoal vapor line to a TBI fuel pump return line, but check to see if your Jeep has a roll over valve on the charcoal vapor return line first.

Many of the emission controls for a TBI system are computer controlled, but to the best of knowledge, the EGR valve for a GM151 is controlled by a vacuum hose, not a wire connected to the EGR valve.

GM used a Vehicle Speed Sensor (VSS) with all the TBI systems, including the GM 151. Aftermarket VSS sensors can be installed inline with the speedometer cable.

Most all the other sensors needed for a TBI conversion are easy to install. The sensors are all wired with a different electrical connector, so getting things wired is easier than you might think. The only part not included in the computer wiring harness is the ALDL connector. Usually the ALDL connector is part of the under dash wiring harness, so the ALDL connector will need to be spliced into the computer harness. Usually only 16 wires are needed to be connected into the vehicle harness. The TBI computer has a need for a couple different power wires. One computer power wire needs power from the battery all the time. One of the computer wires needs power only when the igniton switch is in the start position. I seem to remember that the computer needs a couple power wires when the ignition switch is in the on and start position.

If you have other question about a TBI conversion, send me a private email.
dave

 
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