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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,658 Posts
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 View attachment 583012 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
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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 -
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
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.
 

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1991 Cadillac Sedan Deville 4.9l 80k miles
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78 Posts
Discussion Starter #23 (Edited)
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?
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
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
 

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1991 Cadillac Sedan Deville 4.9l 80k miles
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78 Posts
Discussion Starter #25
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?
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
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.
 

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1991 Cadillac Sedan Deville 4.9l 80k miles
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78 Posts
Discussion Starter #31
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!
 

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White Diamond '03 DHS (with DTS floor shift)
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87,076 Posts
the only one that didnt seem to change was number 6. It was really hard to tell by feel.
Try listening to #6 with a stethoscope or a length of vacuum hose. See if it has the same rhythmic ticking as the others.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,658 Posts
====================
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 -
 

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1991 Cadillac Sedan Deville 4.9l 80k miles
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78 Posts
Discussion Starter #34
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?
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,658 Posts
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?
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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 -
 

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1991 Cadillac Sedan Deville 4.9l 80k miles
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78 Posts
Discussion Starter #36
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?
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
On number 6. Be sure to check plug and wire. If they are firing, then focus on injector.

The front pipe, into rubber, is the pcv pipe. It can be moved away.

Injectors, there are 2 engineering types: plastic tab and or spring wire. Find the tab, press and pull. For the spring wire, you should be able to pull to release. Some older spring wire required a small screw driver to pry the spring wire away from the sides

To get to the wires, remove the intake manifold and use long handle needle nose.

Finally, on the E5.4 test, it's very helpful to put a tachometer on the distributor so you can see the change in rpm.
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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956 Posts
spring clip. Use a pick to pry one side off. That should give you enough clearance on the other side as well.
 

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1991 Cadillac Sedan Deville 4.9l 80k miles
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78 Posts
Discussion Starter #40
I'm pulling the injector or the plug on the plug on the injectors,? Sorry, sounds dumb but I want to be very careful and not break anything.
 
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