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Discussion Starter #1
I posted this in the Pushrod section too.

Lets start a new thread on this subject huh? We have talked about my 4.9 having a rough idle in the DeVille Section under :94 DeVille Idles Rough" and a little more in the Pushrod section under " Car Problems".

Anyway, to do a short recap.....

Idles rough w/out a/c on, in and out of gear, smooths out when load is applied. The TB has been cleaned, EGR replaced and passages cleaned, vac lines replaced, new plugs, wires, cap and rotor, PCV Valve, air and fuel filter.

I have done the power balance test, it passed. Today I did the Injector Flow, fuel Pressure and OHM's test. This is what I got. (Oh yeah...When I tossed the FP Tester in the car on the way home she was idling just smooth as the day she was new. Too bad it didn't last too long.)

KOEO: Fuel Press 40 PSI

Pressure drop each inj:

1. 22#
2. 22#
3. 22#
4. 20#
5. 20#
6. 22#
7. 22#
8. 20#

OHMs Test

1. 12.8
2. 13.1
3. 12.7
4. 12.8
5. 12.6
6. 12.7
7. 12.6
8. 12.9

Now the questions are......
1. The manual says: "Replace injector(s) that had a pressure drop not within 2psi of each other." ...would this cause it, or is this really acceptable?

2. OHMS Test. Manual says 8-25 OHMS. To me that is a pretty broad range. The only two I question are Injs 2 and 8. The rest seem to be within each other +/- one tenth. What do you think?

3. The next test is a Voltage Drop test which requires Essential tool J-39021. I don't have this tool and don't know what it does. But they want me to see if any Inj has a voltage drop of more than 9.5 volts and replace those Injs.

So now what do I do? I'll appreciate any help I can get.

Thanks,
Jason
 

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Jason,
Based on your data, I'd say the injectors are fine.
In any diagnostic testing like this, the book may give you a +/- range that you are JUST outside. in those cases, you can USUALLY assume that you are still ok. That's like saying that if a compression test on the engine shows say 120psi on 7 cylinders, and 110 on 1 cylinder, you should re-ring that one cylinder. Obviously that is NOT the case. If you have a bad injector, it'll be outside the trend of the others SIGNIFICANTLY.
If you have a rough idle, have you tried to verify that it's not a lean-miss? Or maybe a slightly rich condition? Anytime I have a rough idle and a basic tune-up doesn't fix it, I start by feeding the engine a slight amount of propane or similar alternate fuel, or closing off the intake at the carb or throttle body to "artificially" richen the mixture to see if the extra fuel smooths out the idle. You can also do the opposite by creating a slight vacuum leak and seeing if the engine smooths out. If either of these works for you, it'll point you in the direction of the problem.
 

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Discussion Starter #3
Katshot said:
Jason,
Based on your data, I'd say the injectors are fine.
In any diagnostic testing like this, the book may give you a +/- range that you are JUST outside. in those cases, you can USUALLY assume that you are still ok. That's like saying that if a compression test on the engine shows say 120psi on 7 cylinders, and 110 on 1 cylinder, you should re-ring that one cylinder. Obviously that is NOT the case. If you have a bad injector, it'll be outside the trend of the others SIGNIFICANTLY.
If you have a rough idle, have you tried to verify that it's not a lean-miss? Or maybe a slightly rich condition? Anytime I have a rough idle and a basic tune-up doesn't fix it, I start by feeding the engine a slight amount of propane or similar alternate fuel, or closing off the intake at the carb or throttle body to "artificially" richen the mixture to see if the extra fuel smooths out the idle. You can also do the opposite by creating a slight vacuum leak and seeing if the engine smooths out. If either of these works for you, it'll point you in the direction of the problem.
Thanks Kevin. I'll check that when I get home. I was also wondering what the fuel pressure is supposed to be at idle. Could this make a difference or not?

Thanks,
Jason
 

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Discussion Starter #4
Katshot said:
Jason,
Based on your data, I'd say the injectors are fine.
In any diagnostic testing like this, the book may give you a +/- range that you are JUST outside. in those cases, you can USUALLY assume that you are still ok. That's like saying that if a compression test on the engine shows say 120psi on 7 cylinders, and 110 on 1 cylinder, you should re-ring that one cylinder. Obviously that is NOT the case. If you have a bad injector, it'll be outside the trend of the others SIGNIFICANTLY.
If you have a rough idle, have you tried to verify that it's not a lean-miss? Or maybe a slightly rich condition? Anytime I have a rough idle and a basic tune-up doesn't fix it, I start by feeding the engine a slight amount of propane or similar alternate fuel, or closing off the intake at the carb or throttle body to "artificially" richen the mixture to see if the extra fuel smooths out the idle. You can also do the opposite by creating a slight vacuum leak and seeing if the engine smooths out. If either of these works for you, it'll point you in the direction of the problem.
And now for the rest of the story.....

Forcing the system rich only made things worse. Creating a vacuum leak seemed to make things better. I don't know how true this is because once you go above idle things smooth out anyway.

I went into Overrides and shorted out cyls again. The first time I could not tell that much of a difference on #2. Second time around I noticed a difference. Brought timing to 0 deg advance, RPM dropped, idle did not smooth out.

Vehicle Data Stream:

TP .5-.9 Fluctuates with idle
MAP 35-37
BARO 100
ECT 101
IAT 105
Spark Advance 21-25 Changes with idle
Batt 12.7
RPM 600-675
Trans Temp 85
Front Bank Inj Pulse Width 3.4-3.6
Rear Bank Pulse Width 3.4-3.6
Front O2 Volt .12-.79
Rear O2 Volt .14-.76
Front Cross Counts 0-3
Rear Cross Counts 0-4
Front Bank short Term fuel trim 124-128
Rear Bank fuel Integrator 122-136
Front Bank Long term fuel Trim 120
Rear " "119
Prom Cal 516

So where does this leave me now? :bonkers: :wacky:
 

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Cadillac Deville 1998
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I dont know if this will help but here I go.

2weeks ago, when I started my car, it sounded like I pushed on the gas pedal. As soon as i put it on Drive, you can imagine the sound that it made. I went to the garage and we found out that it was the Idle air Control (that's not the exact term for Cadillacs but anyway ...). It measures the exact quantity of air and gas that you need when your engine is whether cold or hot. I changed it and everything was fine after. I don't know if that will help but anyway ! By the way, my English might not be very good i'm from Montreal and English isn't my primary language !! Good luck with your problem !

Peace !!
 

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DOH !! How stoopid I am ... I forgot to mention that on idle, without touching whether gas or brake, I could go up to 70km/h sometimes !

Peace !!
 

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Discussion Starter #7
I stuck the vacuum guage on the engine yesterday. At cold idle it shows a steady reading. On warm idle it floats between 17-19in. From what I know this is supposed to be ignition. Is that correct?

Thanks,
Jason








ga_caddy said:
I posted this in the Pushrod section too.

Lets start a new thread on this subject huh? We have talked about my 4.9 having a rough idle in the DeVille Section under :94 DeVille Idles Rough" and a little more in the Pushrod section under " Car Problems".

Anyway, to do a short recap.....

Idles rough w/out a/c on, in and out of gear, smooths out when load is applied. The TB has been cleaned, EGR replaced and passages cleaned, vac lines replaced, new plugs, wires, cap and rotor, PCV Valve, air and fuel filter.

I have done the power balance test, it passed. Today I did the Injector Flow, fuel Pressure and OHM's test. This is what I got. (Oh yeah...When I tossed the FP Tester in the car on the way home she was idling just smooth as the day she was new. Too bad it didn't last too long.)

KOEO: Fuel Press 40 PSI

Pressure drop each inj:

1. 22#
2. 22#
3. 22#
4. 20#
5. 20#
6. 22#
7. 22#
8. 20#

OHMs Test

1. 12.8
2. 13.1
3. 12.7
4. 12.8
5. 12.6
6. 12.7
7. 12.6
8. 12.9

Now the questions are......
1. The manual says: "Replace injector(s) that had a pressure drop not within 2psi of each other." ...would this cause it, or is this really acceptable?

2. OHMS Test. Manual says 8-25 OHMS. To me that is a pretty broad range. The only two I question are Injs 2 and 8. The rest seem to be within each other +/- one tenth. What do you think?

3. The next test is a Voltage Drop test which requires Essential tool J-39021. I don't have this tool and don't know what it does. But they want me to see if any Inj has a voltage drop of more than 9.5 volts and replace those Injs.

So now what do I do? I'll appreciate any help I can get.

Thanks,
Jason
 

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You're REALLY making me think here!
The battery voltage is low, the MAP and BARO are high (are you right on the water or something?), fuel trim is off a bit. The engine is running a little rich for some reason if you add air and it smooths out. Did you check the fuel pressure regulator? Is the charcoal canister flooded? It's drawing fuel from somewhere my guess is but again without being there, this is tough.
 

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Discussion Starter #9
Katshot said:
You're REALLY making me think here!
The battery voltage is low, the MAP and BARO are high (are you right on the water or something?), fuel trim is off a bit. The engine is running a little rich for some reason if you add air and it smooths out. Did you check the fuel pressure regulator? Is the charcoal canister flooded? It's drawing fuel from somewhere my guess is but again without being there, this is tough.
Sorry about that Kevin! What would cause MAP and BARO to be high? We're at 714 feet, in the north west part of Georgia. When I originally did the EGR I disconnected the canister purge line at the TB and capped off the port. There was no change. I reconnected it the other day and there was no difference.

How would I check the fuel pressure regulator?

I have a feeling that there might be a leaky injector. When you take the air cleaner off it has a very strong fuel smell after sitting over night.

Can you explain exactly what is Fuel Trim?

Thanks Kevin, I guess I owe ya for all this.

Jason
 

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Discussion Starter #10
Katshot said:
You're REALLY making me think here!
The battery voltage is low, the MAP and BARO are high (are you right on the water or something?), fuel trim is off a bit. The engine is running a little rich for some reason if you add air and it smooths out. Did you check the fuel pressure regulator? Is the charcoal canister flooded? It's drawing fuel from somewhere my guess is but again without being there, this is tough.
I put the fuel pressure guage on the car. Ini pressure was 42#, then I turned off the key and the guage connected. from 5:18 to 5:28 it dropped from 42# to 38#. Is that normal or is that saying that something is not holding pressure? :bonkers:
 

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When I said to check the regulator, I meant the vacuum diaphram. They get holes in them and then basically "suck" raw gas through the vacuum line. Usually, a bad one will "piss" fuel if you remove the vacuum line while the car is running. You might want to do an injector "leak-down" test to determine if one or more are bad.
 

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Discussion Starter #12
Katshot said:
When I said to check the regulator, I meant the vacuum diaphram. They get holes in them and then basically "suck" raw gas through the vacuum line. Usually, a bad one will "piss" fuel if you remove the vacuum line while the car is running. You might want to do an injector "leak-down" test to determine if one or more are bad.
Oh, in that case I already checked the regulator.
 
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