Ed Hall

The only other thing I would add to the things mentioned would be a set of exhaust headers. GM must have been counting pennies because these simple mods really wake up these old diesel engines.

A good substitute for the sulfur is 2 cycle oil. I mix 1 oz oil to 1 (gallon) diesel fuel. I also buy my 2 cycle oil at Walmart in the gallon jug.

So far, all is well with the 4.1 to 4.9 conversion. It just needs a little tweaking with the tuning. I'm currently using 350 injectors but it's causes it to run a little bit too rich. So I'm looking for a set of 305 injectors.

To set things straight, the car that the work was performed on was my parents 1987 Cadillac Sedan DeVille. It had 270k miles on the 4.1 and was running pretty shabby. Other than that, the rest of the car was in good shape. The 1988 Eldorado still runs very good. The Cadillacs built from 1988 and up had much improved 4.5 engines compared to the earlier 4.1. The major improvement was roller cams and much more power. Also, the intake manifold gaskets were much improved which decreased the likelihood of coolant getting into the oil and wiping out crankshaft bearings. The Cadillacs that could benefit a lot from the conversion would be FWD Cadillac's with the transversely mounted 4.1 built from 1985-1987.

Here's how the 4.9 engine sits in the car. It runs very smoothly and has tons more power than the HT4100. So far, I'm very pleased with the results and I'm glad that I saved this very well built car from being sent to the crushers and recycled into a Smart car. With only 80k miles on the heart transplant, it should last for a very long time. Also, my homemade exhaust fits like a glove and sounds like some of the more expensive exhaust systems out there. It was easy to do with the engine out. I don't know if anyone else is interested in saving an old car like this but if someone is, I would be willing to write something up on how to do this. The job was not difficult but there was someone planning and homework that went into this to make the conversion successful.

Got it running. I'm currently working out some of the kinks. The exhaust was a major success. It sounds very good and produces just the right level of noise.

Here's what was partly responsible for the terribly low power. Hint... Take a look at what has come out of the end of the pipe. Plugged up all the injector holes on the 4.9 with some bolts and RTV. Those injector holes don't need to be used since I've converted it over to TBI. The distributors are different between the 2 engines but wanted to avoid swapping them. So I swapped the innards instead. I hope it will work. 4.9 engine ready to be installed.

I've heard that too little back pressure could kill low rpm torque. When I replaced the muffler on my 1988 Eldorado, I drove it around the block without the rear muffler and it sounded exactly like you described. It was noticeable, but not objectionably loud. However, I think the catalytic converter also cut down a lot of volume as well. My guess is that it would have been pretty loud without the catalytic converter in place. I got the engine bay pressure washed. It was a terrible mess from all the oil that the HT4100 leaked out. Instead of switching distributors, I took some of the guts from the 4.1 distributor and put it into the 4.9 distributor. I left those 2 connectors (at the bottom of the picture) disconnected because the 4.1 doesn't use those. I hope it works.

The 2 glasspacks will be installed in place of that long large tube down the center. The idea is have a quiet but free flowing exhaust. The glasspacks (absorptive muffler) take out the high frequency noise while the Flowmaster (reactive chambered muffler) cancel out the low frequency noise netting as much sound reduction as possible without causing much restriction. Engine yanked out! Bye Bye HT4100. Anyone want it? Might be good for a riding lawn mower.

I'm hoping the following setup won't be too loud. But if it's too loud, I'll have to do as you suggest. Here's the setup 2 glasspacks in line Plus Flowmaster chambered muffler in the rear.

Exactly, 350 Chevy TBI injectors into the 4.1 throttle body.

Yes, the injectors on the 87 are in the middle of the throttle body. The intake manifold on the 4.9 have 8 injector holes which will be covered shut and the throttle body with the injectors from the 87 will be bolted onto the 4.9 intake manifold. Basically, I'll be changing it from Port Fuel Injection (PFI) to Throttle Body Injection (TBI).

I forgot to mention that average fuel economy on the HT4100 had dropped down to 12 mpg. This is worse than my 1990 3/4 ton Suburban.

This car was the last year that the infamous HT4100 was used. It's got 270k miles on the clock and everything on the car (paint, interior, transmission) is still in good condition except the engine. The engine has had a noisy valve train for a long time but lately, it has been getting progressively worse to the point that everybody could hear it coming from several blocks away. Also, the rated 125 hp was more like 50 hp. The engine would struggle in 2nd gear with the pedal through the metal going up Snoqualmie pass and passed by semi's that were carrying a full load. By the time you got to the top of the hill, 25 mph was as fast as she would go. We did open up the valve covers to inspect the rocker arm support fixtures for cracks and they were fine. So most likely, the camshaft and cams were wiped out. Anyways, long story short, we were given a 4.9 out of a 1992 Seville with 80k miles on it. The decision has been made to put this engine in place of the 4.1. The plan of action is the following: 1. Block off all the injector ports on the 4.9. 2. Bolt down the 4.1 throttle body to the 4.9 intake manifold 3. Transfer all the accessories over to the 4.9 4. Use 350 Chevy injectors 5. Bolt the stainless steel 4.1 exhaust manifold onto the 4.9 6. Use the 4.1 distributor 7. Modify exhaust system to have 2 glass packs in series and replace the back muffler with a chambered muffler. Replace this With this 4.9

I applaud your efforts for keeping an older but high quality car on the road. In this bad economy, there will be more people rethinking about buying new and end up keeping their old car running. You should end up with a nice running car once the swap is complete. I wish you the best of luck and do keep us posted.