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THOLTZ

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After looking through the site to no avail I figure I have to post the problem we’re having with our Caddy.Here is the particulars on the car. It is a 92 Seville 4.9L V8 PFI with 70k miles. My wife’s dad gave us the car. Garage kept, any time the car needed anything it was taken to the dealer. No past history of any serious trouble. Now for the problem, which I believe is in the engine coolant temp circuit somewhere. Turn ignition switch to on, engine temp reads 7deg. Start engine, engine starts but very rough idle and black smoke for a minute or so then it smoothes out and the smoke goes away. After what would be considered enough time for normal operating temp to be reached the engine temp reads any where from 80 to 108 degrees. It seems to run fine other than the rough start-up and it’s mass consumption of gas. I understand that the computer thinks it’s cold and therefore increases the amount of fuel delivered. I have checked various sensors and have replaced the temp sending unit and one more located in the intake ( don’t remember the name of it) and it still has the same problem. With the ign. Switch on(engine cold) I disconnect the connector to the temp sens. And the temp reading on the dash goes down to –35 degrees. I short across the conn. Pins the rad. Fan comes on and the instrument cluster reads Engine over heat or something to that effect. Now the strange thing to me is when I remove the jumper wire (switch still on) the temp reading is now closer to what it should be (ambient) aprox. 81F, I now plug the conn. Back into the sending unit and turn the ign. Switch to start and what do ya know, the dang thing fires up like nothings wrong, no stumble, no rough idle and no black smoke. The engine temp reading goes to what I think it should be when at normal operating temps (I let it run for awhile) around 185 to 190 degrees. But as soon as you turn the ign. To off the whole thing goes back to the low temp reading rough start-up etc. I can duplicate this over and over. It’s just hard for me to believe it’s the PCM but that’s why I’m throwing it out to the experts. Has anyone ever bought a PCM from NAPA? Are they good or bad? BTW it’s not giving me any codes. As always any help would be greatly appreciated. Sorry for the long post.

THOLTZ

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Welcome to the forum. The 92 Seville is a fine car, and the 4.9L overall has been very reliable.

Guesses/Things to eliminate:

Head gasket failure, allowing water into the piston during cold start, hence the smoke/rough running when cold, and slowing proper heatup? Are you losing any coolant? Any exhaust gases in the coolant (test kit)?

Stuck/dripping fuel injector? Similar to above, but too much fuel going into the piston on shutoff or on startup and does not clear til running? Check by pulling the injectors out and observing them while spraying, or have them flow checked.

Can you reproduce the smoke/rough idle only when the engine is actually cold?

So if you drive it for an hour, then park for 4 hours, does it smoke/run rough, or only if parked overnight?

Bruce

2016 Cadillac ATS-V gray/black

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Thanks for the welcome and reply Bruce, I am quite certain that it isn't head gaskets, intake gaskets or injectors but I wouldn't bet my life on it lol. This thing is about to drive me nuts. It isn't temp sensitive, that is, it does it when its cold and after it has been run for miles, in other words any time you turn the engine off and then start it, it goes through this smokey stumble untill it clears up, which takes about 30 to 45 seconds. It kind of reminds me of my old Ford truck that the choke would hang up on. I have discovered how to make it think everything is ok by turning the ign switch to on and shorting the coolant temp sending connector pins together with a jumper wire, then remove the jumper and reconnect the connector back to the sending unit while the switch is still in the on position. Then I can turn the ign switch to start, the engine fires up like nothings wrong But once the ign. switch is turned to off its back to square one. One thing I didn't mention is that the idle is slow to come down, like pulling up to a stop sign it just takes longer than it should. Thanks for the help!

Tony

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I'll try to go through the cold start info in the 92 manual later today and re-guess.

It does sound like something in the cold start system is confused, but I wonder why if that were the case it is not posting an error code. Have you checked the onboard diagnostics, or are you using a code reader, or do you mean that it is not showing an error light or message in the driver's information center?

See the how-to section here: http://www.caddyinfo.com/howto.html for how to use the onboard diagnostics to check codes.

Bruce

2016 Cadillac ATS-V gray/black

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If ECM thinks it's cold theRPM at start should be very high... Did you check the FPR fuel pressure regulator for leaks? Just pull the vacuum line of the FPR if any fuel comes out the nipple when car is on it is bad. Replacing the ECM with a known good one takes seconds.

Oh forgot... welcome to the board!

The saddest thing in life is wasted talent

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Had a problem something like yours with my 92 seville, it would stumble on startup run rough for a few minutes then smooth out until the temp got up to 175 then it would start to stumble and jerk like crazy and the temp reading would jump to around 235 and the message would come across "engine hot shut down" replaced everything that I could think of with the advice of the great guys on this board, still the same, until one day Old Gamer" replied the my post and said to replace the PCM and told me to get one from the salvage yard since there are no moving parts in it, you just have to remove your PROM ship from the old one. Got it for $50 bucks put it in and every since the that car has run like new no problems what so ever and it has been about a year now. You can look up our old posts just do a search if you think that they will help, good luck.

DL

BTW- The Cadillac Dealer/Stealer told me that my headgaskets were blown and that it would cost me $4000 :ph34r:

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I'll try to go through the cold start info in the 92 manual later today and re-guess.

It does sound like something in the cold start system is confused, but I wonder why if that were the case it is not posting an error code.  Have you checked the onboard diagnostics, or are you using a code reader, or do you mean that it is not showing an error light or message in the driver's information center?

See the how-to section here: http://www.caddyinfo.com/howto.html for how to use the onboard diagnostics to check codes.

"Have you checked the onboard diagnostics" Well, I'll say I've made an attempt and have had some results but I'm just not too sure of the accuracy of the data I was getting only because I'm not real up on caddy code as of yet. I will however be trying it again tonight to see if I get the same or different results. I'll post them later.

"are you using a code reader" no sir I'm not.

"or do you mean that it is not showing an error light or message in the driver's information center?" The only thing that comes up is Service Ride Control but thats been happening since we've had it, was told by pa in-law it was ok. I'm gonna spend a little time in the How To section. Thanks for the link!

Thanks,

T

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adallak, downlow... Thanks for the input, no I haven't tried that (FPR) check yet but I will. Right now I'm leaning heavily toward the PCM and I'll hope for the best! Thanks for the welcome and thanks for the help.

Tony

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