1983 Cadillac Seville HT410 Pops/Backfires from Throttle Body

[Vinny6t6]

OK........before I start, I know all about the dreaded HT4100.  Here's the thing........My 17 year old son found a 1983 Seville with 85k miles that he fell in love with.  He wants to get into the hobby and is proud of his car.  It ran beautiful and has a great ride. He put fuel injection cleaner in the tank and on the way home it started popping/ backfiring from the TBI.  I checked the error codes and there are none.  I checked the timing and its not 10 degrees before TDC like the manual says but at 14 degrees BTDC.  I checked the fuel pressure an it's 14 PSI so I am ruling out fuel pump.  A lot of forums say it's the cam and I'm hoping it's not.  I'm beginning to think the fuel filter may have clogged.  It runs beautiful at idle, but when given gas, it pops.  Please help.  I'm used to my 66 DVC and 83 Riviera Conv with a carb.  BTW, where is the distributor hold down clamp nut?  I cant see it at all!!

[Dan LeBlanc]

Popping through the throttle body, timing at 14 degrees not at 10 degrees and nobody has changed it sure sounds like a valve timing issue to me.  I think the events of adding injection cleaner and the beginning of the popping are merely coincidental.  The popping through the throttle body is because the cylinder is getting spark before the valve is closed - increased engine RPM = Increased advance = spark plug firing with the intake valve still open.

Either something gnarly happened with the cam (which these engines are known for) or the timing set has jumped time.  Prepare for the worst, hope for the best.

[Vinny6t6]

I just ordered a 13mm/15mm Distributor wrench from summit racing.  I will set it to factory specs one I A. Get the distributor wrench in the mail.  B. Find the hold down clamp nut.  I appreciate the feedback.

[Jeff Rosansky CLC #28373]

However it turns out congratulate your son for getting into the hobby. My son felt in love with a 55 we found and it is a lot of fun (especially since I get to drive it while he is at college). My son drove it to school multiple times and there is even a blurb about the car and him in the yearbook.
No matter how it turns out, enjoy!!
Jeff

[Eric DeVirgilis CLC# 8621]

I once had the exact same symptoms in a 4 year old 1983 Fleetwood Brougham with 39,000 miles. The issue was due to a soft camshaft which was another of the HT4100 maladies which have largely been forgotten.

Thankfully the factory covered the repairs at the dealership despite being just outside the warranty period. (GM was anxious to make up lot of PR ground back in those days) The repairs were finished in the astonishingly short time of just 2 days, the technicians almost able to do the job in their sleep having done so many up to that point. 

Car was sold to a customer who just two years later experienced the same exact problem due to the replacement camshaft which was apparently just as soft as the original had been.

By all means check all the usual suspects first but if nothing helps, a bad cam would be my guess.

If you do manage to get it sorted out, my earnest advice would be to sell the car and put the money toward one of the earlier models with cast iron block 425/368 powered Cadillacs from 1977-1981 which have far and away better reliability than the dreaded HT4100 can ever hope to be. 

[76eldo]

My memory of foggy but there is a wire somewhere near the master cylinder area that you have to do something with when you set the base timing.

Google it to be sure.

The backfire through the TBI is not a good sign.

[Vinny6t6]

I appreciate everyone's input.  I hope it's the timing but my gut tells me it's the cam.  I've done a cam/lifter/timing set replacement on my 66 myself, but the HT4100 has so many hoses and tubing on it.  Parts are cheap and it may be a good winter project for him to learn on. he has the shop manual. I'll be there every step of the way, but I think it's overwhelming for him

[Vinny6t6]

I'm thinking of replacing the motor with a 368, 307 or 350.  has anyone done this?  What motor would be a straight bolt in?  How about computer? Wiring, etc.  I'd rather go this route than fix the 4100

[Dave Shepherd]

I was a Cadillac factory employee during the HT  4100 debacle.  The root cause for cam failures turned out to be the exhaust guides in the head were machined too tight, when they got carboned up they tended to bind in the guide causing an additional load on the cam lobes.  Hence repeated failures. Code 30 and popping in the intake were the most common symptoms.  Of course the metal contamination in the oil eventually scored the bearings, more trouble.

[SixDucks]

If you're willing to replace the 4100 with something other than another 4100. I suggest installing any Oldsmobile small block engine. That's what Cadillac did..... at least on the rear drive Brougham. These cars could be ordered with a 350 Oldsmobile diesel engine so parts for a conversion  can be found. Look to the Buick Riviera or Oldsmobile Toronado for any needed engine mount brackets if they are any different than the 4100. I suspect they may in fact be the same. Any 307 - 403 small block Olds can be bolted in. With careful measurements you may be able to verify that any Olds big block fits also. (Hood clearance is the issue but if you use a Toronado intake I think it clears.)
Others may follow with more suggestions.
P.M me with your phone number if you want to discuss this.

Terry

[Scot Minesinger]

Six ducks has a great idea.  Teenagers have more time than us.  My son and I worked on a 1970 SDV together, and he did all the sanding, scraping and grinding that typically is the most laborious part of the process.  Your son can research and find an engine, read the manual on how to remove and reinstall while you supervise.  Then he can research all the tedious tasks of hooking up the climate controls, sensors for dash read outs and etc.  He will learn a lot and you both will have more fun.  It keeps him busy too.

[bcroe]

Diesel conversion parts for an Olds with a carb is going to be the
most simple approach.  Most Riv/Toro of those years will already
mount an Olds small block.  The smaller FWD starter ring gear must
be used, do not know if the 4100 fits, but it was used on all the
Olds powered 79-85 FWDs.  A 403 will provide a real performance
boost, needs a bigger 3 inch single exhaust system.  good luck,
Bruce Roe

[Jeff Rosansky CLC #28373]

but I think it's overwhelming for him

He is probably disheartened. I, and most of us, have been there. He found a car he loved and could afford and now this is happening. Close to the end if the world for a teenage car guy with no $$. He is probably more upset about this than if his girlfriend dumped him.
Just be there to support him (sounds like you are).
I don't know the costs involved with just a cam swap but if it's reasonable maybe do it now to get it back on the road and then take your/his time researching the engine swap.
This may not be the smartest solution, but just thinking about it from his perspective. Getting it back on the road asap is probably the most important thing to him.
Jeff

[Scot Minesinger]

Jeff is right.

Plan on the engine swap and do all the prep work (buying the used engine and getting all parts) you can and maybe help him out with some of the $.  Drive the Caddy anyway since engine will be swapped.  Then maybe when use of a car is less critical maybe around holidays swap engines.

[fishnjim]

Doesn't sound logical that a good running motor would trash the cam with a dose of injector cleaner.  What was the rationale for additive add?   
I think there's a little anxiousness and not much lets work this thing out going on here.   Already changing the motor when problem hasn't been diagnosed? 
Take the TBI off and check it and the flow module.   Take the valve covers off and check the valves.   IF it's the cam, they'll not B move'n right.   

[TJ Hopland]

Just make sure you are following the correct procedure to check and set the timing.   There will be a specific way to put it into timing set mode.  There were a lot of variants so don't just assume its the same as a different year or model car.   Later years its a jumper in the diagnostic connector but I too am thinking earlier was disconnecting something under the hood unless I am confusing that with the GM's with carbs and computers.

Besides the cam issues the other thing these engines were known for was tearing up the distributor drive gears.

The hold down bolt is where you would expect it to be but not easy to get to on the longitudinal engines.   The transverse engines its a little easier because its not so far back.  Be glad you don't have a RWD car, those were almost impossible.   

[Vinny6t6]

You guys have made me rethink everything.  Jeff Rose......you're right he's really upset.  I'm helping him every step of the way and told him that you have to kiss a few frogs before you land a princess.  We've all been there.  I'm going to buy the parts for him and he's doing the work, but I'll be right next to him.  One thing he had over me when I was growing up is at least I have all the tools he needs and he does not have to go borrow or spend his money on it.  Fishnjim.....you're right.  I'm taking it one step at a time.  I'm setting the timing first.  If that does not work, I'll pull the valve covers and check the lift.  I figured if I get a replacement engine from a junkyard or private seller, I don't know the history and chances are they are high mileage, need work and I have to get everything like the climate control, ECM, and sensors to work together.  I did the research and a new cam, lifters, timing set, distributor and engine gasket set is about $500.  I've done this before and I'll show him how to do it.  Good winter project for him and it'll ad one more person to this wonderful hobby of ours.  I've always told him anyone can go out and buy a new car or a classic that has already had all the work done to it, but nothing gives you satisfaction like knowing you did it yourself.

[Dave Shepherd]

If the cam is bad the real issue is the engine  is loaded with metal, the filter does not get it all trapped. As  I stated above, it was a common  issue for bearing failures down the road. That engine should not be run any more without an immediate oil change.  Then cut the filter open and look for metal debris.

[TJ Hopland]

A crude way to check the cam would be pull the valve covers which isn't too bad a job on those and use a straight edge across the rockers while its running looking for one or more that isn't moving as far. 

[James Landi]

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.  Go figure. In any case, I think Glenn Brown will have some insights. If your interested in going that route.   James Landi