sixtyfiveford Posted December 8, 2014 Report Share Posted December 8, 2014 I have a 1992 Cadillac Deville that stumbles/vibrates on medium-hard acceleration. If I'm cruising and I dump the gas pedal it will stumble but if the tranny down shifts it will act very smooth and peppy. So it seams to just have a misfire at the mid rpm range. Assumtion was misfire so I pulled the plugs and #1 & #8 were souty black. So they shold be my culprite. Here is what has been done: -New Plugs -New Wires -New Cap & Rotor -New Fuel injectors out of a Crown Vic (yellow top) -New Fuel Filter -High octane premium fuel -Fuel Pump tested good (around 45-50psi if I recall) -EGR tested good No Check Engine codes are present but there are some reoccurring Service Vehicle Soon Codes: E91(PRND123 switch) , E61(Cruise Control), E98(P-N D-R issue(only once)). All of these things made a very minor difference and maybe no differnce at all and it's just in my head. But still acts the same. Where should I go from here? Link to comment Share on other sites More sharing options...
KHE Posted December 8, 2014 Report Share Posted December 8, 2014 Remove the air inlet piping to the engine and hold the throttle plate wide open by the linkage. There will be two EGR tubes about 1/2" in diameter. If they are plugged up with carbon, take a screwdriver and rod them out and vacuum out as much of the crud as you can. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
barczy01 Posted December 8, 2014 Report Share Posted December 8, 2014 ECM had problems with those cars and would cause a misfire. Fuel injector harness was an issue, loss of injector pulse. Link to comment Share on other sites More sharing options...
KHE Posted December 8, 2014 Report Share Posted December 8, 2014 The fuel injectors themselves could also be an issue on the 4.9 engine. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
sixtyfiveford Posted December 8, 2014 Author Report Share Posted December 8, 2014 Remove the air inlet piping to the engine and hold the throttle plate wide open by the linkage. There will be two EGR tubes about 1/2" in diameter. If they are plugged up with carbon, take a screwdriver and rod them out and vacuum out as much of the crud as you can. I'll take a look at this. Link to comment Share on other sites More sharing options...
sixtyfiveford Posted December 8, 2014 Author Report Share Posted December 8, 2014 The two EGR ports: One closest to front of car was spotless and the other had mabye 1/32" of light carbon that I cleaned off. I pulled the plugs in one of the known misfire cylinders #8. It is new(15minutes of running) and it is already getting sooty black, signifiing misfire. I decided to do a compression test on this cylinder to rule that out. It jumped right up to 160psi, compression is great. I threw my timing light onto the #8 lead so I could watch for spark pulses. It seams good but I wasn't able to test it under load. Link to comment Share on other sites More sharing options...
barczy01 Posted December 9, 2014 Report Share Posted December 9, 2014 unplug the egr valve and drive to see if it helps. Link to comment Share on other sites More sharing options...
KHE Posted December 9, 2014 Report Share Posted December 9, 2014 Have you checked the fuel pressure upon acceleration? It should not drop off. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
sixtyfiveford Posted December 9, 2014 Author Report Share Posted December 9, 2014 The fuel pressure stays steady with acceration(just under 50psi). Just thinking: If the spark plugs are blackening with a rich mixture, wouldn't this signify no spark or an injector that is injecting to much fuel? The same cylinders have fouling with the different injectors and all new wires/plugs/rotor/cap. So installing new different items made no difference. Testing spark to the cylinder tests good so could the injector be recieving signals to fire excessively or when it's not its turn? Link to comment Share on other sites More sharing options...
KHE Posted December 9, 2014 Report Share Posted December 9, 2014 Based on the fuel pressure readings, you can conclude the fuel pump is good. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
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