Yokie Posted May 13, 2011 Report Share Posted May 13, 2011 1999 STS, this started last fall but went away. When the outside temp is above 80 deg or so he engine will have a miss intermittently. The hotter the temp the worse it gets. There are no codes posted. Changed the plugs cleaned the TB and EGR no change. Running the AC makes it worse but its still there when off. I need to get this fixed before vacation next month. Thanks in advance. Link to comment Share on other sites More sharing options...
Göran W Posted May 13, 2011 Report Share Posted May 13, 2011 Are you absolutely sure there is no codes? SES light on? Link to comment Share on other sites More sharing options...
rockfangd Posted May 14, 2011 Report Share Posted May 14, 2011 could be wrong but it sounds like a overheating coil. the warmer it gets the more it misses GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
Yokie Posted May 14, 2011 Author Report Share Posted May 14, 2011 No codes at all. Very sure of that. Has anyone had a coil pack overheat before? Link to comment Share on other sites More sharing options...
Yokie Posted May 14, 2011 Author Report Share Posted May 14, 2011 No codes at all. Very sure of that. Has anyone had a coil pack overheat before? Link to comment Share on other sites More sharing options...
Yokie Posted May 14, 2011 Author Report Share Posted May 14, 2011 No codes at all. Very sure of that. Has anyone had a coil pack overheat before? I just took a hair drier and heated up each coil with no change. Could a clogged fuel filter cause this? Link to comment Share on other sites More sharing options...
Yokie Posted May 14, 2011 Author Report Share Posted May 14, 2011 Well I bought a coil pack and tried it in all four positions no change. Link to comment Share on other sites More sharing options...
Texas Jim Posted May 14, 2011 Report Share Posted May 14, 2011 Have you checked the resistance of the plug wires. As temperature increases... resistance increases... A wire with high resistance may be causing your miss... Link to comment Share on other sites More sharing options...
Ranger Posted May 15, 2011 Report Share Posted May 15, 2011 Could a clogged fuel filter cause this? No. I'd suspect the wires as well. Link to comment Share on other sites More sharing options...
Yokie Posted May 17, 2011 Author Report Share Posted May 17, 2011 Well now its 50degs and its still missing. So much for the heat only affecting it. I drove it over 100 miles on the interstate and sometimes under hard acceleration I could feel it stumble. Pulled the codes when I got home pulled a U1064 serial data failure that's all. I don't see how that could be related. Going to replace the plug wires next..... Link to comment Share on other sites More sharing options...
BodybyFisher Posted May 17, 2011 Report Share Posted May 17, 2011 Well now its 50degs and its still missing. So much for the heat only affecting it. I drove it over 100 miles on the interstate and sometimes under hard acceleration I could feel it stumble. Pulled the codes when I got home pulled a U1064 serial data failure that's all. I don't see how that could be related. Going to replace the plug wires next..... You should not just parts replace. Check the ignition wires with an ohm meter and record the resistance along with the length of the wires in inches. Determine the resistance per inch the bad wire will stick out. Also look into both ends of the ignition wires and look for burned out cores that happens but that should show up with the resistance test You dont want to simply replace them without checking them out. By the way, heating the coils with a hair dryer is not a good way to diagnose them, what you did by buying one and swapping it into each position is a good way to diagnose a bad coil What concerns me is that you do not show a code for a misfire, with that kind of miss, you should get a P030x code set. No P0300's at all? No flashing Check Engine Light? Typically a problem that gets worse with warm up and that is intermittant we have seen is the PCM, it could also be the ignition module, keep that in mind. Have you determined which cylinder is misfiring? Do you smell fuel? GORAN asked you a question is the SES light on? You did NOT respond. This is a BRAINSTORMING session, we will feed off of each other here. Please answer questions DIRECTLY. Like this>>>> No the SES is not on, or Yes the SES is on, or the SES is flashing... that is clear A flashing CEL/SES indicates a misfire is occurring. Please check resistance of wires, inspect them closely, check for vacuum leaks also a vacuum leak can cause a miss. Has the intake manifold been off recently? Are you losing coolant? Is it overheating at all? Have you used any injector cleaner? Don't use it, I am just asking. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Yokie Posted May 18, 2011 Author Report Share Posted May 18, 2011 Well now its 50degs and its still missing. So much for the heat only affecting it. I drove it over 100 miles on the interstate and sometimes under hard acceleration I could feel it stumble. Pulled the codes when I got home pulled a U1064 serial data failure that's all. I don't see how that could be related. Going to replace the plug wires next..... You should not just parts replace. Check the ignition wires with an ohm meter and record the resistance along with the length of the wires in inches. Determine the resistance per inch the bad wire will stick out. Need to purchace a new one might do it to day then test Also look into both ends of the ignition wires and look for burned out cores that happens but that should show up with the resistance test will do maybe today You dont want to simply replace them without checking them out. By the way, heating the coils with a hair dryer is not a good way to diagnose them, what you did by buying one and swapping it into each position is a good way to diagnose a bad coil What concerns me is that you do not show a code for a misfire, with that kind of miss, you should get a P030x code set. No P0300's at all? No flashing Check Engine Light? As said no codes except U1064. No other lights on or flashing of any kind. Typically a problem that gets worse with warm up and that is intermittant we have seen is the PCM, it could also be the ignition module, keep that in mind. Have you determined which cylinder is misfiring? No, and how would you do that inspect the plugs amd wire ends? Do you smell fuel? No and also inspected the FPR vac hose no fuel there. GORAN asked you a question is the SES light on? You did NOT respond. This is a BRAINSTORMING session, we will feed off of each other here. Please answer questions DIRECTLY. Like this>>>> No the SES is not on, or Yes the SES is on, or the SES is flashing... that is clear A flashing CEL/SES indicates a misfire is occurring. No flashing lights or dash lights of any kind. Please check resistance of wires, inspect them closely, check for vacuum leaks also a vacuum leak can cause a miss. inspected for a vacuum leak can find none Has the intake manifold been off recently? No Are you losing coolant? Is it overheating at all? Never overheats in the 6 yeays I have had it and coolent level is steady I check it weekly Have you used any injector cleaner? Don't use it, I am just asking. I tried some last year when problem first surfaced and tried some again yesterday Techron with Sunoco 93 then an Itialian tuneup. It seemed to happen less but it is still there. need to drive it some more today. Link to comment Share on other sites More sharing options...
Yokie Posted May 19, 2011 Author Report Share Posted May 19, 2011 Just tested the plug wires. They ranged from 2.5K ohms to 2.9K ohms per inch. I would guess that would be in spec. I thought about reseating the PCM, any thoughts? Link to comment Share on other sites More sharing options...
the gold2 Posted June 1, 2011 Report Share Posted June 1, 2011 You might check the coolant temp. sensor. Do you have a MAP sensor?, egr solenoid? check them also. sticky valve maybe? lazy O2 sensor(s) ? Good Luck ! Link to comment Share on other sites More sharing options...
the gold2 Posted June 1, 2011 Report Share Posted June 1, 2011 "Running the AC makes it worse but its still there when off" hey did you perform the idle learn procedure? The AC on means engine under load. Idle learn procedure includes AC on for load conditions ! Link to comment Share on other sites More sharing options...
BodybyFisher Posted June 1, 2011 Report Share Posted June 1, 2011 I believe you have 4 coils on that engine correct? Pull the ignition wires out of each coil and inspect the contacts in the coil for corrosion, you might buy a small wire brush and clean them, also, when you plug the wires back in, be sure there is a positive tight connection at the coll. Have you pulled the plugs and looked at them? They sometimes lose their platinum pads and you may have a bad plug Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Yokie Posted June 5, 2011 Author Report Share Posted June 5, 2011 "Running the AC makes it worse but its still there when off" hey did you perform the idle learn procedure? The AC on means engine under load. Idle learn procedure includes AC on for load conditions ! I removed and cleaned the MAP, EGR and idle control awhile back with no change. It is missing at speed now but intermittently. Still no codes at all. Also the hotter the weather the worse the miss. Link to comment Share on other sites More sharing options...
BodybyFisher Posted June 5, 2011 Report Share Posted June 5, 2011 Ok just saw that you bought a coil and swapped it in with no change It hard to remember what was done and not done sometimes Check for vacuum leaks, snug down the intake manifold bolts and see if any seem loose What kind of fuel are you using (grade) Have you put a fuel pressure gage on the fuel rail to check pressure at idle? Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Yokie Posted June 7, 2011 Author Report Share Posted June 7, 2011 Ok just saw that you bought a coil and swapped it in with no change It hard to remember what was done and not done sometimes Check for vacuum leaks, snug down the intake manifold bolts and see if any seem loose What kind of fuel are you using (grade) Have you put a fuel pressure gage on the fuel rail to check pressure at idle? First I disconnected a plug wire and it didn't have the same sound or symptom as what I was experiencing. With this in mind I really began to suspect the fuel system. I didn't have a gauge to check the pressure so I replaced the fuel filter. So far so good and the filter was severely clogged as I could hardly blow through the inlet side. Thanks for all of your help and suggestions. I will update this in about a week. Link to comment Share on other sites More sharing options...
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