I have a 91 deville with a 4.9l. I have done a lot of diagnostic for a apparent miss. I had a tune up which was supposed to be new plugs, wires, fuel filter, cap, and button. That was a year ago.
Still, the miss continued. I speculated on this board about it possibly being the fuel pump. I checked the fuel pressure. It seemed normal. That being said I cant drive the car and look at the gauge cause the tester hose isn't long enough to tape to the windshield. It was said the coil might be an issue so i ended up replacing the whole distributor and internals. Still the miss continued.
The miss doesn't start at ignition. It seems to start at higher speeds like getting to 60mph on the interstate and works it's way all the way down to where traveling 20mph becomes very challenging. Its definitely happens quicker when the temperature out side is higher. When it gets that bad the car stahls easily without the accelerator. Now the kicker is if when it's at the worst if the car can set for say an hour. The miss is a lot better or gone for a while. The only other odd piece of information is when I totally fill the tank the miss seems to occur almost always.
I'm kinda to replacing the fuel pump. My concern is spending the money for a fuel pump and it ends up being the way more expensive sending unit.
Is it possible that there is something wrong with the plugs, wires, or fuel filter that would cause my problems. I'm not getting any engine codes. Have no idea if that helps or not but figured I'd say. Also, I had the catalytic converter tested and it was 100% fine. Please help!?!
My first thought is fuel pressure. Clogged filter or sock on the pump...or a failing pump.
Somehow,get that pressure gauge hose lenghtened and taped to the windshield.
How many fuel filters are there. I'm thinking fuel pump because of the apparent temperature variable. Is there anyway that replacing the (I'm guessing external) fuel filter cause these issues? It was supposed to be replaced. Another fact is that this car does have the typical issue of stalling when fuel level is low and you brake and turn left. I've read that there is a baffle issue in this model. Can this be related. Also, the car starts to act up when electronic fuel system says it has 4 gallons left ie stalling, lurching, like it's out of fuel.
Another fact is that this car does have the typical issue of stalling when fuel level is low and you brake and turn left. I've read that there is a baffle issue in this model. Can this be related
How's it run with a full tank of gas?
Gas gauges of this period have been known to be erratic.
I've reset my trip odo at every fillup, and when it gets to be around 300, I'm probably runnng on fumes. Just a check on what the gas gauge reads.
As for the filters; one on the left frame rail, and one sock on the pump pickup.
Again, a fuel pressure gauge will nail a fuel delivery problem.
Most severe at 1/4, but will start acting up at 1/2 with sharp stops and jack rabbit starts.
You probably have a bad fuel injector. Known problem with the 4.9. On cold start, you are running open loop with the ecu running a higher idle until the car warms up. This extra idle is compensating for the missing cylinder (bad injector). Once on the road, where the power is needed, the missing cylinder becomes obvious. Now the car is warmed up, in loop, reduced idle so when you come to a stop, you are unable to maintain a good idle.
There is a power test via the diagnostics that allows you to deactivate each injector. Once deactivated, the idle rpm should drop 50-75. If it doesn't drop, then that injector/wire is bad.
I cannot find a complete guide on how to use the computer to diagnose problems. I printed a small post but it was about getting readings more than turning things off and on. Is there a post I can print with the complete guide. Also, I don't think the baffles are the issue at all. I was posting all information I had. The injector problem sounds solid but why does the problem go from accelerating above 60mph to not being able to go up hill 10mph. If I dont feather the pedal I cant go anywhere. It progresses kinda quickly after about 10 mph. The temperature variable is why I dont think fuel filters. Is it possible the fuel pump is overheating? And a dumb question, what's the fuel sending unit do? The fuel pump sends the fuel right?
I cannot find a complete guide on how to use the computer to diagnose problems. I printed a small post but it was about getting readings more than turning things off and on. Is there a post I can print with the complete guide. Also, I don't think the baffles are the issue at all. I was posting all information I had. The injector problem sounds solid but why does the problem go from accelerating above 60mph to not being able to go up hill 10mph. If I dont feather the pedal I cant go anywhere. It progresses kinda quickly after about 10 mph. The temperature variable is why I dont think fuel filters. Is it possible the fuel pump is overheating? And a dumb question, what's the fuel sending unit do? The fuel pump sends the fuel right?
why does the problem go from accelerating above 60mph to not being able to go up hill 10mph. If I dont feather the pedal I cant go anywhere. It progresses kinda quickly after about 10 mph.
None of this sounds fuel pressure related to me. If you don't want to pay the big bucks for a FSM you can buy a CD version or download version for about $15. That will tell you everything you need to know about the OBD. I'm wondering if your catalytic is clogging. A simple vacuum test would verify that.
I got an e31 code for map sensor. I have already replaced the map. Any ideas? My battery never seems dead but there seems to be a draw because when I hook up the charger it never is at 100%. Could a less than 100% battery cause my problems?
Pigtail/wire harness is probably gone. Also, vacuum hose might have a leak.
Here is level one of the diagnostics. P02 will show what the map sensor is reporting.
Cadillac diagnostics
To enter the diagnostics system, simultaneously press and hold the OFF and WARMER buttons with the engine running until the system activates. Any diagnostic codes will display first. When the system prompts you with .7.0 you want to press the LO button. This will force the sytem to the PCM data mode and the display will show E.9.0 Use the HI and LO buttons to scroll thru the PCM data parameters. Here is what you can access....
P01 throttle position in degrees
P02 MAP (manifold absolute pressure) in kPa
P03 computed barometer in kPa. Subtract MAP from BARO to get engine vacuum
P04 coolant temperature in degrees C
P05 MAT (manifold air temperature) in degrees C
P06 spark advance
P07 battery voltage
P08 engine RPM....tach
P09 vehicle speed MPH
P12 injector pulse width
P14 oxygen sensor voltage
P16 oxygen sensor cross counts...a measure of O2 sensor activity
P18 closed loop integrator (128 ideal...less equals leaning, more enriching)
P20 closed loop block learn value (same as above)
When driving with the diagnostics activated the icons on the climate control panel stand for other functions....kind of like tell tales on an instrument cluster....
rear defog is the VCC status
front defrost is 4 gear status
ECON is the o2 sensor status (on is rich)
AUTO is the closed loop status
OFF is the closed throttle switch status
OUTSIDE TEMP is the AC compressor request
F is the AC low pressure switch status
C is the heater water valve status
AUTO FAN is the cooling fan command status
I was driving while reading p02. It clearly varied between 26 at idle and 93 while about 55mph and missing. Also while in that mode I noticed in the eatc the econ and auto lights were off and on at random. What does that mean?
ECON light should vary. It's reporting when the o2 sensor is reading rich or lean which changes depending on acceleration, idle, etc.
If the AUTO is cycling, then you are dropping in and out of closed loop. The ECU will change fuel trim and idle depending on loop status, which might be causing the miss.
I had the same problem with closed loop status that was causing poor mpg. A new thermostat was opening too soon, causing the engine to run cooler than spec. The temp sensor read that angle was not warmed up and would change the loop status.
Dear Friends, I had a similar problem with my 1988 Deville, 4.6 Liter. My mechanics finally figured out that there was a gap in the gasket at the injector housing. Does that make sense? This was several years ago. Air was leaking in and messing up the fuel air mix. The repair was cheap
as I recall, and the car has run like a champ since then. Oh, I just got the horizontal surfaces painted and the rest of the body polished. Man, does it look good! I wish mom were around to see it, as Big Red was her car. The silver 2008 in the background is my daily driver. Ed
========================== Dear Friends, I had a similar problem with my 1988 Deville, 4.6 Liter.
your car did NOT have a 4.6 Liter motor -
1988 was the first year for the new 4.5 motor - a VAST improvement over the infamous HT4100 -
the first Deville with the 4.6 Northstar was the Concours model in 1994 -
I replaced the thermostat. The map sensor. I was looking at the coolant temp through diag system and I thought it was weird it was less than 100 degrees after driving 30 minutes. I changed the thermostat because I had a coolant flush. They said it was really bad. Wanted to charge extra to work on the heater core. I said no. I've always thought that the heater never was a hot as it should have been. seem better after flush and thermostat but not spectacular. since the flush it seems I'm losing coolant. Anything I said jog anything loose? What is the appropriate temp for coolant after the car is warmed up?
Thermostat should be 180 not 160/165 which are options. I put the wrong one in and had to switch to correct the temp problem. Double check your purchase/installation
I replaced with a 195 degree thermostat. I was talking about the coolant temp being in the 90 degree range. if the computer loses data from the o2 sensor would that cause it to switch between closed and open loop. If it has a bad connection and was sending data off and on would the loop status change just as quick? How many 02 sensors does the 4.9 have?
Sounds like water temp sensor is bad. The close loop is based on engine temp. It's also possible (I'll have to check) that it'll drop out of it doesn't receive data from its sensors:
- O2, map, air temp etc.
You can monitor the O2 using P14 and P16. P16 shows how often the O2 cycles which should be in the 4-8 range. (P14 shows actual voltage, but is not fast enough to show the voltage fluctuations).
P18 and P20 are equivalent to STFT and LTFT. average should be 128. If it is less, it indicates that the engine is running rich (based on O2) and is trying to lean out.
You are running in open loop with extra gas being provided. The system is ignoring the sensors waiting for the water temp to rise. So signals for P01-P16 are valid.
Ok misspoke on the display. Auto wasn't blinking which indicates it was in closed loop. O2 sensor isn't an issue. I got my FSM and wow that's alot of info. I was looking in the inboard diag system stuff. Under pcm output overrides I saw E.5.4 the injector override. I was told to try that to see if it feels different on each injector. If not that might be a bad injector. the only one that didnt seem to change was number 6. It was really hard to tell by feel. I also saw E.6.0 the injector flow override. what does that tell you? Is there any other ideas I can use to test engine related miss options? Paying attention as someone told me. I think I have a miss right from startup but the car adjusts so I didnt notice before!
==================== the only one that didnt seem to change was number 6.
as Ranger suggested - LISTEN to each injector -
you can aslo use an OHM meter and measure the resistance of each injector -
they should be almost identical -
How do you get in a position to listen to the injectors? I have a stethoscope but I'm probably being dumb. I just cant figure out how you would listen to each one. As far as ohms are the wires for the injectors in the plastic wire protector that runs with the fuel rail and into a plug by the distributor? If so. Is there a list of what pairs to measure?
Also, I used 93 octane because it says to on the car. Even with that fuel it still sounds like its rattling ie knocking. Is that normal or is that part of my miss problem?
==================== I have a stethoscope but I'm probably being dumb. I just cant figure out how you would listen to each one.
with the engine running - find a path for the probe and touch each injector -
As far as ohms are the wires for the injectors in the plastic wire protector that runs with the fuel rail and into a plug by the distributor?
to PROPERLY measure the resistance of each injector -
you MUST unplug the harness from the injector and measure the resistance DIRECTLY at each injector -
there are no shortcuts -
do it RIGHT - or don't bother doing it at all -
Ok, I realized I had to direct measure after I posted. I wasn't short cutting. Just lost my marbles for a second. There very hard to get to. Any suggestions or am I supposed to remove anything? I can get a needle nose on the plug but I cant see how to release it. Is there a method or just pull. I really dont want to make it worse. I'm doing all this to figure out what is or is not my problem. A lot of people tell me it's the fuel pump. And older guy told me today if the car starts to miss put it in reverse and drive backwards up a hill if the miss stops it's the fuel pump. That was so far out of left field and I couldn't rationalize it so I thought I'd mention it.
On the front side of engine (side closest to the front of the car) I can remove one metal tube. It's just pushed into a rubber hose. The fuel rail sets over top of the plugs for the injectors. Do I move it somehow or work around it?
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Cadillac Owners Forum
4.8M posts
369.7K members
Since 2002
Cadillac Forums is the perfect place to go to talk about your favorite Caddys including the ATS, CTS, SRX, Escalade, LYRIQ, Vistiq, concept and future Cadillac models.