Need help with 85 Eldo HT4100 Tuneup
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HT4100 4.1, 4.5, 4.9 Discussion, Need help with 85 Eldo HT4100 Tuneup in Cadillac Engine Technical Discussion; First, a short history, I have had this car for a couple of years, used to run great, a few ...
  1. #1
    SpittingAngels is offline Cadillac Owners Member
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    Need help with 85 Eldo HT4100 Tuneup

    First, a short history, I have had this car for a couple of years, used to run great, a few months ago started having problem with rich exhaust Code 45 intermittently but ongoing. Exhaust smell became stronger with fuel odor, not sulfur though. Idle was rougher, would surge but during driving this wasn't noticeable. At first, acceleration alone would make the code go away but in the last couple of months it would stay set for longer periods of time. Replaced air cleaner, vacuum lines, oxygen sensor. Air filter was getting dirty pretty quickly, seems to be because of an exhaust leak in engine compartment.

    Found and plugged a tiny hole in exhaust pipe coming out of driver side manifold that was causing exhaust leak in engine compartment. This seemed to fix air filter issue. However, issues persisted. Exhaust noise seems a bit louder since then as well. I cleaned off the engine a bit, it was pretty dirty. The underside is still dirty but the top looks ok.

    I replaced all spark plugs about a week ago, timing was a bit off before at 12 degrees, specs say it should be 10. After spark plugs replaced, I waited to adjust timing because I had to special order a Bosch wireset. Since then Code 45 has been near constant, as well as an intermittent Code 13. I replaced the distributor cap, rotor and wireset last night and performance was worse. Engine is noticably louder and rougher and upon first startup after this, I was getting Code 34: MAP signal too high. I played around with a vacuum tube under glovebox and took air cleaner off and checked vacuum lines under there and Code 34 went away but engine still very rough, cut out a couple of times when I revved the engine high.

    I still need to adjust timing but I'm not sure if it would cause this type of behaviour, I'm still a novice but I have shop manuals and pretty intelligent, just lack experience in maintaining and repairing cars.

    I checked EGR valve diaphragm and it moves, but not easy, not sure how resistant it should be.

    I have a few questions that my manuals don't really answer:

    1. Where is the distributor hold down bolt for this model engine? Manuals say to adjust but no pics/diagrams and I can't find it. I bought a distributor wrench but it may be wrong shape, they had two types, S-shaped and U-shaped and I bought the S-shaped one because the label said for all GM V8 engines.

    2. The advance timing seems to be controlled by ECM, I think I need to disconnect something to set initial timing but adjusting distributor.

    3. I have order on distributor cap correct, I'm sure, I triple-checked this. The old wireset was numbered, driver's side cylinders were 1,3,5,7 and passenger side was 2,4,6,8. This corresponds to info in one of my manuals but I've seen some posts here online that say #1 would be on passenger side. I'm worried the roughness might be crossfiring but I'm not sure how to tell. Can you tell by the sound and can anyone confirm if my manual info is correct?

    4. Assuming I get questions 1 and 2 answered and the roughness and rich exhaust issues persist, what should I focus on next? I've seen posts here about the EGR valve, my manual also talks about a charcoal canister and I'm wondering if the stronger fuel odor could be related to that and how to check.

    I plan on taking into a shop for exhaust system work but I want to do as much other maintenance on my car myself as possible. I love this car and up until recently it performed very well for me, I want to be able to give it the TLC it deserves. Sorry for so many questions in one post but I've been reading my manuals a lot and also some prior posts in these forums and I really want to make sure I adjust my timing right and know where to focus from there.

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  3. #2
    awadecki is offline Cadillac Owners Enthusiast
    Automobile(s): 76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
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    Re: Need help with 85 Eldo HT4100 Tuneup

    This is a tough one. First off, where is the fuel odor coming from? The tailpipe, or in the engine compartment? It sounds like from your codes that the engine is running too rich, causing the rough operation. Here's what I'd do based on your symptoms.

    The MAP sensor on this car is crucial to engine operation. Go to an autoparts store and buy a replacement (about $20-30). Connect it properly, ensuring that the vacuum line from the TBI to the sensor is crack free. Restart your car. It could be that the internal diaphram in your sensor is getting sticky. If the engine runs 100% after switching out the sensor, you found your problem. If not, just disconnect it and return it to the autoparts store--they won't know you used it. Just tell them you bought the wrong one. Easy way to eliminate the MAP as the cause of your problem. At the same time, you should check to make sure the throttle body mounting bolt torque is in spec to ensure no vacuum leaks.

    Next, the timing...I've never owned a longitudinally-mounted 4.1 engine, but I do know that the hold down bolt is very hard to reach and/or find on it. All I can say is to look around the base of the distributor, where it mates to the intake manifold. 12 degrees is fine for this motor--in fact, I wouldn't touch it. It's giving you a bit of extra power. Although, after reading your description, I'm doubting that you've checked the timing properly. On this 85 Eldorado, i'm not sure if you jumper the A&B terminals of the ALDL connector under the dashboard, or disconnect the 4-pin connector at the distributor. In any case, you MUST check the timing while doing one of these things in order to put the car in fixed time (i.e. no advance) mode. Recheck your timing using the correct procedure. Timing at idle in advance mode is about 15-16 degrees, so if you're reading 12 degrees, your actual base timing may only be 7-8 degrees, in which case, you could have jumped a tooth on the timing gear.

    If the MAP doesn't solve your problem, I'd look at replacing the EGR valve. If you can't move the diaphram freely (you should be able to push it up fairly easily and smoothly), this could be stuck open, causing too much exhaust to be recirculated, and hence, the computer will try to compensate based on what it sees as a lean condition. Here's one trick to testing the EGR. Start your car and get out a hammer. With it running, hit the top of the EGR hard--you won't hurt it. Of course, don't demolish it, but hit it pretty hard. This usually will release the diaphram if it's stuck. If your engine operation smoothes out, replace the EGR valve. If it hasn't been replaced in a while, you may want to replace the EGR anyway.

  4. #3
    SpittingAngels is offline Cadillac Owners Member
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    Re: Need help with 85 Eldo HT4100 Tuneup

    ok, I found the green connector in the back of my engine I have to disconnect and the distributor bolt.

    I also think I found the culprit of my problems. there was a short length of vacuum hose connecting the TBI to a stiff black hose that I presume runs to the map sensor. It was rotted and almost ripped in half, I missed it when I replaced my vacuum hoses a few months ago. I also found a couple of other hoses in the back of the engine that could use replacing as well. Man, I hope that's it...to think a small 2" piece of hose could could so much problems.

    I want to proceed with timing adjust but I can't get the green connector disconnected. I recall last night, looking at the diagnostics panel, the value for the advance timing being detected was 18 so maybe I'm not too far off after all and misreading it. I'll keep messing with it but I hope I don't break this wire clip that's giving me trouble. I wish I could read the label on the front of my engine compartment, would've save me a lot of trouble. Once I learned what I had to do from my manual and these forums, I was able to read what was still legible on the label to confirm I'm on the right track.

  5. #4
    SpittingAngels is offline Cadillac Owners Member
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    Re: Need help with 85 Eldo HT4100 Tuneup

    Ok, well I gave up on the connector. I've attached a pic of it, sorry the image isn't better focused but it's a royal pain to get to and I had a hard time even aiming the camera at it.

    On the bright side, after replacing the vacuum hose I discovered, my Caddy is purring about as good as she was before. I guess that hose must've been rotting and when I replaced the distributor last night, I pulled on that hose and made it worse, bad enough to trigger the map sensor error.

    The spark advance the ECM is reading now is 25 so I still think I need to adjust the timing and bring it down a bit but at least she is drivable now. I've got a smaller hose in place of the rotted one so I'm going to get the correct size and get that one and the other couple of hoses I found replaced tomorrow and afterwards have another crack at that connector. Any suggestions or tips would be greatly appreciated. As you may be able to make out from the pic, I have pushed back the clip on the side and the connector wiggles but it just won't pull apart and I can't get a good enough angle to take a closer look at it. there a couple of loose male clips elsewhere in the engine compartment that look the same but they are not mated with a female connector so I'm worried there is another catch that I'm missing. I've pulled very hard and I'm afraid if I pull any harder I'll rip one of the wires out.
    Attached Images

  6. #5
    awadecki is offline Cadillac Owners Enthusiast
    Automobile(s): 76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
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    Re: Need help with 85 Eldo HT4100 Tuneup

    Hold on there on the spark advance. That value is not based on what the ECM "sees" the engine running at. It is only a value that should agree with what you find on a timing light. In other words, changing your timing will NOT change the value displayed by the ECM. Check your timing following the proper procedure before moving anything. As I said, I don't know if this entails jumpering 2 pins on your car (as is the case with my 85 FWD Deville) or disconnecting the wiring harness at the distributor (as is the case with early 80s GM cars).

    Usually, though, the distributor connector is a 4-pin connector on older GM cars...you may have the wrong one.

    You need to read the emission control label on your car, or the service manual before doing anything. If you hear no "pinging," your timing is likely not too far advanced.

  7. #6
    SpittingAngels is offline Cadillac Owners Member
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    Re: Need help with 85 Eldo HT4100 Tuneup

    Well, here's my VECI label. With the help of my factory manual, I was able to decipher it and step 5 reads "Disconnect green reference signal connectors on engine wire assembly at rear of engine near distributor." It's actually easier to read from the photo than on the car

    That's the only green connector I could find in that area, it's practically right behind the distributor. But it's a single blade plug, not a 4 pin connector, as I've seen mentioned here and there on these forums. I included another shot of the connector and the wire harness that it's connected to.

    But, no pings and I took her out for a short test drive and she's sounding a lot better. I can't see what the initial timing is without getting this stupid connector apart though.
    Attached Images

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