: Bad Misfire on Low Mile 4.9 (1991 Eldorado)

04-21-11, 12:27 AM
Hi Everyone,
I am getting ready to sell a very cherry 1991 Eldorado Biarritz that belonged to a great aunt. It only has 52,000 miles and was always stored in the garage here in California. It also received regular proactive mechanical maintainance. The only real mechanical issues it has (up until two days ago) is an engine oil pan leak and a leak at a transmission cooling tine. I am an ex ASE master tech, maybe a little rusty since its been a few years but these items are nothing too serious for me to repair.

But, after driving it for a few days (getting it waxed, cleaning the interior, etc) it all of a sudden started running poorly. It feels like one cylnder is not firing. Not terribly noticeable at an idle, but as soon as you take off it feels like someone pulled a plug wire. I inspected the plug wires and there is no external signs of issues (I know that doesnt mean much). I pulled the plugs and they all had the exact same greyish color. The plugs, cap and rotor were worn so I replaced them all with no change in the running condition. It is embarassing, but I sold my timing light since I haven't used it in such a long time. I need to borrow one ~ I was thinking of attaching it to each plug wire to see if there is spark ~ do you think that would be helpful or sould I just pull each wire and use an old plug to check for spark? I guess I should have also done a compression check while I had the plugs out, but the mileage is so low I am just assuming that internally the engine is still solid. I was also going to pull each fuel injection connector off one at a time and watch for the idle to stay the same to possibly pinpoint a clogged or malfunctioning injector. That is when I found out that the injectors and their connectors are almost impossible to get to without removing the fuel injection hard lines (and that does not look like much fun). Are these injectors known for clogging? Are there any good tips & tricks anyone can recommend that would be good short cut to diagnosing what is going on here?

Thanks in advance!

04-21-11, 01:36 AM
After doing some more reading it seems like this could also be a possible bad injector. If so, I will probably upgrade all the injectors to the new Bosch 4-hole. I saw mention of a way to turn off each injector using the info center. Can anyone explain the entire procedure or provide me a link to the procedure?

Thanks in advance.

PS ~ recently sold my Z06 Corvette ~ thinking about getting a CTS-V. :)

04-21-11, 08:03 AM
Since it's been sitting around so much I would give it some fresh gas and add some Techron to it. Hopefully that will clean out you injectors. If you haven't checked for codes yet there is a sticky in the 4.x section that explains that procedure.

04-21-11, 10:45 AM
Thanks ~ I added fresh fuel 100 miles ago and it has benn running well up until a few days ago. I wasn't sure how often the 4.9 injectors expierience 'clogging' problems verses having an electrical or mechanical problem. That is why I am requesting help on how to turn off each injector. Also, I can ohm out each injector if someone can help me with the color coding on the injector harnesses.

04-21-11, 10:58 AM
Codes are:

I'm not too worried about the twilight sentinal code right now but how important are the other two?

04-21-11, 07:07 PM
Those codes are nothing to worry about and are unrelated to the engine.

Unplug the injector harness and look straight at the terminals. Now turn it so that it stands straight up. The + and - for each injector is on the left and right side respectively. You'll figure it out when you see it. Each injector lead has a unique color stripe. Be aware that one pair of leads in that connector are for the coolant temp sensor. Acceptable range is 12-17ohms.

Here's an explanation of how to navigate the diagnostics. It's copied from another thread:

Here is a page with instructions for reading the codes:
http://www.cadillacforums.com/forums...x-engines.html (OBD I codes for 4.x Engines)

Navigating the system is simple once you know what each button on your climate control represents. Think of it this way:

Hi = 'YES'
Lo= 'NO'

Warmer = 'ENGAGE' or 'MORE'
Cooler = 'DISENGAGE' or 'LESS'


After entering diags by holding 'Off' and 'Warmer' for 3 seconds, codes will be displayed one at a time. After the list is finished it will say "ECM?"

Answer the 'question' by pressing the Hi button. Then you'll see "ECM DATA?" Answering yes (Hi button) will put you within the ecm data section where the TPS value is displayed. Answering no (Lo button) will display the next section in the ECM and so on. You navigate within the system by answering yes or no until you get where you want to be. The Warmer and Cooler buttons are used in the ECM OVERRIDE section to engage/disengage various systems such as the ISC motor. Just mess with it for a while and you will get the hang of it. It's just questions and answers!

In your case you will want to go ECM? > ECM OVERRIDE?> INJECTOR while the engine is running in park.

The cylinder number will display in the climate control. Holding 'Cooler' will disengage each one.

04-22-11, 07:16 PM

04-22-11, 08:38 PM
Bingo ~ thats exactly what I needed. Happy Easter!

04-22-11, 08:40 PM
PS ~ its also for sale. A true creampuff!


04-22-11, 11:56 PM
Holy s*** dude, that's clean. Mileage? Price? Location?

04-23-11, 12:29 AM
Get an old spray bottle and spray the exhaust manifolds with water with it running. The dead cylinders wiil be more than obvious.

04-23-11, 12:35 AM
52,850 miles ~ one owner & always garaged in Southern California. $6500 obo :)

You can click on this link to see a detailed walkaround video:



04-23-11, 01:16 AM
That's a beauty! Wanna trade me for a hacked up seville?:contract:

04-23-11, 02:19 AM
Man...that's nice. That's the same color my first Caddy was (1992 Sedan Deville). Loved it. Looks black in indirect light, looks blue under the sun.

That's a little rich for my blood at 20 years old, but I don't think you'll have any trouble finding a buyer. Looks fantastic.