1983 Cadillac Seville HT410 Pops/Backfires from Throttle Body

[bcroe]

I had my 4100 on my Eldorado converted to a small block Olds.   Our CLC president purchased it from me several years ago.  The conversion has several challenges, but, believe me, it is doable, and as a side note, we dropped the original 4100 electronic distributor into the Olds engine, and the Cadillac's ecm manages many of the Oldsmobile's engine operations.   James Landi 

Was that the Olds 260, pretty close to the original engine displacement? 

Bolting in an engine is not a huge challenge, the chassis was set up to
accept a wide range of 8 and 6 cylinder engines.  The issue is getting
all the support stuff into good shape, such as fuel pump, ignition
control, and all the rest of engine management.  A bigger engine will
beg a bigger exhaust and cooling system.  Bruce Roe

[SixDucks]

....
  A bigger engine will
beg a bigger exhaust and cooling system.  Bruce Roe

Agreed.  Order a radiator for the diesel to meet the engines cooling requirements. You will likely need a fan shroud for the diesel as well. The local exhaust shop should be able to fabricate a suitable exhaust.
I would have some concerns about a heavy footed driver and transmission longevity though.

Terry

[James Landi]

Bruce--- we used a 260 Olds with a two barrel carburetor...as I stated, the 4100 (high tech) ECM distributor works to manage the Olds.   Main challenges--- creating a cross over exhaust, reconfiguring the throttle cable set up, mounting the transmission shift lever. Some of the "bracketry" for drive belts, etc.  but it was all doable.   I could not tell any difference in performance, although the car now is slightly more "bow" heavy, and slightly less fuel efficient. Major difference:  Can take the car on the highway and don't have to worry about engine failure.  James

[bcroe]

Bruce--- we used a 260 Olds with a two barrel carburetor...as I stated, the 4100 (high tech) ECM distributor works to manage the Olds.   Main challenges--- creating a cross over exhaust, reconfiguring the throttle cable set up, mounting the transmission shift lever. Some of the "bracketry" for drive belts, etc.  but it was all doable.   I could not tell any difference in performance, although the car now is slightly more "bow" heavy, and slightly less fuel efficient. Major difference:  Can take the car on the highway and don't have to worry about engine failure.  James 

I suppose trans life is more a matter of how heavy your foot is, than
engine size.  The Olds small blocks are all pretty much the same
weight, so a 5.0L, 350, or 403 would all work out.  I doubt the 260
Olds was used in the Toro/Riv, but the 5.0L was with its 4 bbl carb
brackets being common.  That trans in a Riv did manage to contain
the turbo V6 T Type, even more powerful than my 403.  Bruce Roe

[James Landi]

An interesting side note on the 260 Olds conversion is that having driven 4100's many miles and many years, the Olds had comparable performance....i.e. just enough power to haul the Cadillac around and no power in reserve.    Would I convert another 80's Eldo convert--- you bet.   I love these cars, and the 84-85 convertible is an especially lovely car if one can afford to do the "transplant."

[Vinny6t6]

OK......here's an update.  I pulled the valve covers and the passenger side was spotless.  The drivers side was black from backfiring.  I ordered a cam, lifters, pushrods, gaskets and distributor gear.  It's a great feeling working side by side with my son and explaining to him what everything is for and what I'm doing. I started the teardown yesterday and did it the right way with ziplock bags and masking tape to label where all the wires went.  Ordered the FSM for the torque sequences and I know I'm going to need help putting some stuff back together.  The best part is what I can "Automotive Archeology"  The cut and spliced wires, missing connections, broken vacuum hoses, etc...  I found two things I've never seen before.  One: One of the alternator wires was replaced with speaker wire.  Two: the previous owner must have ran a wire across the engine bay for something and used.........get this......wire from an extention cord you would use in your house! I have a heated garage so I can take my time.  I'm going to look at every wire and solder in new ones where necessary.  Don't want my son's car catching fire.  Good thing is, all the brackets that I took off, he want to degrease, sand and paint them so it looks good going back.  I have to wait for the FSM to continue, because I can figure out how to take the PS pump off!

[TJ Hopland]

I don't remember 83 specifically but if there are holes in the PS pulley you should be able to stick sockets through those holes and access the bolts.   If there are no holes and the whole bracket can't easily unbolt off the motor then you likely have to remove the pulley to get to the bolts.    Pulley needs a special puller.  They are fairly universal and not that expensive these days.

What is your theory on how a backfire is making one valve cover dirty?   I don't remember these that well is it typical GM V engine where the PCV valve is on one cover and the breather to the air filter housing is on the other one?   If so which side is the dirty one? 

[76eldo]

Vinny,

Please consider this URGENT.  DO NOT ROTATE the engine with the heads off.  Cadillac had a tool that is like a bar that bolted across the cylinder liners to keep them down in case you needed to rotate the engine with the heads off.

Here's why... The liners will rise up off of their O ring seat at the bottom.  This block being aluminum uses steel cylinder liner inserts and the pressure of the piston and ring will move the liner up.  There is an O ring at the bottom that may tear and then you will be pulling the engine.

Get the updated manifold seal and bolt kit and be very careful to torque the heads back down exactly as the manual states and hope and pray that you don't tear the threads out of the aluminum block. 

Good luck,

Brian

[SixDucks]

Vinny,

You will need to get a power steering pulley removal tool to remove the pulley from the pump. I think I purchased mine from NAPA. After the pulley is removed you can access the bolts that are used to secure the pump to the block.
The harmonic balancer must be pulled from the crankshaft. When you reinstall the balancer use a balancer installation tool. I bought mine from Kent Moore. You may be able to utilize a balancer installation tool from Moroso. I'm not certain the Moroso tool will work, though I've used mine on multiple engine makes that require a press on balancer.

Hope this helps.
Terry


P.S.

The path you're on is closely paralleling my own from many years ago. Lots of work and time followed up by catastrophic engine failure leading me to the path with an Oldsmobile engine on it. Mine was a stunning 82' Seville D'Elegante.

[35-709]

"Lots of work and time followed up by catastrophic engine failure leading me to the path with an Oldsmobile engine on it."

May be too late to for this since you have already ordered the parts but please consider what has been said.  You are throwing good money and a lot of time at an engine that was dicey at best from day one.  That engine could self-destruct at any time once you get it back together.  A much better project with your son would be to swap a better engine in the car as has been detailed previously in this thread and then he would have something eminently more reliable and trustworthy and far less worrisome.  My opinion.

[Scot Minesinger]

35-709 is 100% correct.  Plus I drove my Grandmother's brand new 1982 Cadillac with the 4.1 and ...

[79 Eldorado]

If the OP were to do a swap to an Oldsmobile motor I think a good question is what would need to change. To do a swap at least need the donor motor should come with the entire set of brackets (most olds set-ups have similar layouts across car types). The A/C suction-discharge hose assembly looks like it is absolutely different. I suspect if you want the cruise control to work you would need to find a lot of parts from an Olds equipped car. That part would be interesting. Is the AC HVAC module the same; 1983 4100 vs earlier Olds 350 in the Seville? Sometimes they are specific because they occupy so much space under hood. As long as the SB Olds fits it's not a big deal if you need to get a custom suction/ discharge hose set anyway but the module still needs to fit. What about the fan shroud? The motor mounts are normally specific and normally specific to the motor and the car. It seems like a stupid question so I hope the answer is yes but are new motor mounts still available?

Has anyone posting actually done this swap? I have a couple of spare Olds motors and when I was looking for my car I specifically looked for a car which came with an Olds motor. Maybe I was wrong but I thought because the layout of the 4100 was seemingly so different I would be forever chasing things to swap in an Olds motor.

Are the later versions of the 4.1 the same basic geometry? If yes are a lot of the issues sorted. I think the 4.1L was offered in Cadillacs up to around 1992. Regarding the Olds 260 those didn't have the best reputation either but it seems it may have been partially due to small oil returns in the heads which wasn't an exclusive issue to the 260. I would try to get either an older 350 (better oil returns, stronger block, and 10 valve cover bolts as opposed to 5) or a 403 (more displacement) if I wanted to try it.

Interesting topic.

Scott

[Vinny6t6]

I was very confident on this cam swap until I saw 76eldo's post.  I was thinking of using an engine from an 83 riv.  Best part is, I have an 83 Riv and can use it as reference.  I ordered my parts from rock auto.  I think they have a 15% restocking fee.  may be worth it

[bcroe]

Any Riv or Toro with Small Block Olds or a diesel engine
should supply the brackets, exhaust manifolds, and heavier starter
you may need.  The diesel flex plate will not work (except, with a
diesel starter) do not know if the 4.1 will work. 

I have driven the better half of a million miles with SBO s of late
70s, they went to 5 bolt valve covers, lighter castings, and bigger
head bolts for 350/403 in 1977.  I had ONE 350 that had an oil
drain back issue when I got it, had gotten clogged from poor oil
change attention and was leaking out the valve cover.  This is not
fatal, oil can go down the pushrod holes.  I managed to clear the
passage with a coat hanger and never had it again with my
frequent oil changes.

I found the 403 heads still had the metal in place for 10 bolt
covers, so most of mine got carefully drilled and tapped for 10
bolts on my drill press.  Might even make a jig so I can do it
without removing the head. 

Despite expectations I have found these engines extremely
reliable.  No failures, not even worn one out.  I did find a 403 in
the junkyard someone had cracked both heads on by running
with no coolant.  I put used heads on the short block and ran it
another 100,000 miles, think its overhaul time.  Bruce Roe

[79 Eldorado]

Bruce,
I agree with your comments regarding the Olds SB even the newer ones. The older ones have some advantages but I've had "newer" ones as well and they've been reliable for a lot of miles. I did buy a car with reported small amount of blue smoke upon start-up but then goes away. I decided to check it further because it seemed like it was consuming oil more so than smoking a few minutes after start-up. Between the 2 heads 2 of 4 returns were completely plugged. There was so much oil in the head I think it was being sucked around the valve guides. I used music wire and a cordless drill to break the "log jam" and then I used diesel fuel and a test tube brush to thoroughly clean them. I changed the valve seals and it's been perfect since (also changed the oil when I finished the job but goes without saying).

As far as saving an '83 Seville by sacrifing a Riv or a Toronado.... Everyone has their own opinion but if everything was in the same shape corrosion wise I would take a Toronado or Eldorado first, the Riv second/third and the Seville would be in far last place. I never liked the styling of the trunk area of those. The prior Seville was very nice but 80-85 IMO not so much. If I was the OP and really wanted the Cadillac I would probably find an Eldorado/ Toronado or Riv. I would drive it without swapping any engines. When the body finally gives up due to corrosion* only then would I swap the engine into the Seville. That would save the initial work and the son would have a lot of time to know if the E/K body was something he wanted to have in the future. There will be plenty of father/son repair/improvement projects on anything as old as the cars we're discussing.

*The corrosion comment is based on my area..not certain where the OP is from. The transmission as we know is another weak link and based on my experience more so with the TH3254L than the 3spd TH325.

Scott
PS: I really thought about drilling and tapping the extra valve cover bolt positions. In the end I didn't do it because I was concerned about trying to do it while the engine was still in the car.

[76eldo]

There are some parts you will possible need from the donor car for the axle support which boots to the side of the engine and will be different.

Try to locate Cory Heisterkamp on line. He’s done some 403 Olds swaps into HT4100 cars and has all the facts for doing these swaps.

He’s on Facebook.

[bcroe]

My experience has been good with the TH325, its due to be refreshed
at this age, and the accumulator spring replaced, that got me past
200,000 miles.  Less known is the faulty differential gears, which could
crack off some gear teeth around 100,000 miles with absolutely no
warning.  Do not know when this production problem was finally fixed,
3 of mine failed over time.  The TH325L4 might do about as well? 

Avoided all those issues here, the 79 E has a 403, 67 Eldo TH425
switch pitch trans, and 78 E differential.  Bruce Roe

[76eldo]

I didn’t mean to talk you out of fixing your engine. If the parts didn’t cost too much  you may want to go for it and maybe get some more time out of the car.

Swapping is not easy, certainly not as easy and putting the engine back together.
I just wanted to caution you against rotating the engine without the heads on it.

I made that mistake on an 85 Eldo and pulled the engine out and had it rebuilt. It ran great afterwards but I sold it and got a 76 Eldo.

[Vinny6t6]

76eldo......you did not talk me out of it, just gave me the insight that was looming in the back of my head.  I started to get a little "iffy" when I pulled the valve covers and saw that the intake manifold and heads look like they are one piece.  That's why I am looking over the service manual and may give a swap a try.  I have removed and replaced many engines over the years.  The toughest being a 2000 Jaguar K8 with all of it's electronics and special tools needed.  I located an 85 Riv in a junkyard that has 70k miles on it and I can hear the engine run before it's pulled.  It's a 307 and he wants $400.  The only difference, I believe is that it has a carb and the Seville is a fuelie.  That means fuel pressure and other electronics will be fun to handle but it's a winter project and he's excited.  I really appreciate everyone's input and tons of questions you have answered for me.  My son wants reliability not performance so that's why I'm thinking the 307.

[76eldo]

Get every bracket you can off of the donor car because you will need to fab some things and I do remember reading that the Olds has something doffeeent on the axle bearing holder bracket that bolts to the side of the engine.