: Bucks, sometimes stalls only under load



brooksbronco82
12-20-10, 10:42 AM
Hello all, I've been lurking around this forum and fixed quite a few things on my grandmothers car for her with the help of this forum and the search function. Forums like this are great and you guys are one of the Best!! Now I could use some advice.

It's a 2000 cadillac base deville 4.6l with no PCM codes in powertrain. recently has been bucking whenever rpm's go over 1300 and sometimes stalls when slowing to a stop. I do have a scantool but can only pull the generic OBD data.

fuel trims go anywhere between -12 to -18 and timing advance goes to -55 or so.

I can get more numbers if needed and I am leaning to Crank sensors but no codes is frightening me from ordering a couple costly parts.

Any advice is welcome and appreciated.
Brooks

brooksbronco82
12-21-10, 02:42 PM
Hi all, I have my grandmother's 2000 base Deville with 4.6l that is having some real drivability issues. When in gear and reaches 1300, rpms start to fall off quickly then back up, would call it galloping or bucking like. Sometimes will stall while driving or slowing to a stop.

1. No crank sensor codes but do get a P0101 MAF sensor code. Pulled the intake (lots of caked on carbon in that thing) and the plenum wasn't torn but the back side of the TB is definitely needing cleaned. Idles well and will run and do the same thing with MAF unplugged. Short fuel trim goes to 20 and timing advance goes to like 55 or above. both seem high and was looking for an air leak.

2. Theres something right underneath the plenum screwed to the intake with 2 screws. Was expecting a over pressurization valve on the other side of the intake, next to the PS pump, but there isn't. Maybe this is it just on the other side?

Submariner409
12-23-10, 11:18 AM
That 1 1/4" dome under the plenum IS the manifold overpressure valve. Its location changed during the intake manifold design change which came at the start of the 2000 model run.

Because your MAF is divorced, ANY air leak at or after it will result in poor performance, mixture problems, and even total stalls. You can remove and clean the MAF with throttlebody cleaner, but be very careful of the 3 tiny heated resistors across the bridges. Don't mess with or distort the honeycomb flow straightener - it's not a screen - it's 1/4" thick.

Check all the flex intake duct and MAF clamps for integrity and tightness.

brooksbronco82
12-23-10, 03:06 PM
Wow sub, thanks for the picks!! Appreciate the detail in the post and your extensive knowledge. I think that overpressure valve was leaking because there is dirt build up all around it i'm guessing from oil vapor so i'm getting a new one. Also I think the PCV grommet and the rubber piece connecting to the intake are also hard and leaking. I'm hoping it's just these parts and every thing is good. I'll keep the thread updated.

brooksbronco82
12-23-10, 03:23 PM
sorry about this thread, I'm new and thought I did it wrong when I couldn't find it the next day and tried again in the Northstar Performance forum so now I have 2 threads about the same problem. I don't know how to delete this thread.

Submariner409
12-23-10, 03:53 PM
You'll play hell trying to find just that manifold valve. Do some online surfing and get the whole new manifold: it's impossible to clean them due to the folded runners and main log - retail new is about $260, but I'll bet you can find one for half that.

Submariner409
12-23-10, 05:20 PM
sorry about this thread, I'm new and thought I did it wrong when I couldn't find it the next day and tried again in the Northstar Performance forum so now I have 2 threads about the same problem. I don't know how to delete this thread.

Maybe a moderator will merge the two............you don't need a scan tool - go up in the sticky posts at the top of this main forums page and read/study the entire post "How to pull codes" from your car's built in scanner/reader/memory. The 2000 is OBD-II, so use the proper link in the sticky to get to the master Index of all P,B,C, and U codes. You need to write all your codes down, noting whether each is Current or History, then get the definitions and come back to Northstar Performance.

Submariner409
12-23-10, 05:22 PM
Just saw your other thread up in Deville - maybe a moderator will merge the two in here.

Ranger
12-23-10, 10:56 PM
Threads merged.

brooksbronco82
12-24-10, 12:28 PM
Thanks Ranger for merging the threads and for going easy on the Newb!

Sub : I probably should get the whole intake because the carbon is very thick and now is the time to do it. My GM dealer could order the valve with spring and housing for $17 which didn't sound outrageous. I had them order it but will now see if I can find a whole manifold somewhere. The only P code I got thru the Cadillac method was the p0101 MAF code. I cleared it and went for a short drive again and got the same code so I think I can assume that we are on the right track. Parts I ordered won't be in till Monday. I'll update with any progress

brooksbronco82
12-29-10, 12:34 AM
OK, just got finished putting the new pressure valve, intake gaskets, and plenum in and still bucking and jerking with all the same readings. Pretty sure i've eliminated all possible air leaks when I had Intake off. Unless it's EGR or something like that. Going to unplug the battery to reset the computer and see if anything changes. If that doesn't work do you think cranksensors are next? It is a 2000 and not sure on the history of them.

Submariner409
12-29-10, 12:32 PM
OK, just got finished putting the new pressure valve, intake gaskets, and plenum in and still bucking and jerking with all the same readings. Pretty sure i've eliminated all possible air leaks when I had Intake off. Unless it's EGR or something like that. Going to unplug the battery to reset the computer and see if anything changes. If that doesn't work do you think cranksensors are next? It is a 2000 and not sure on the history of them.

That engine has a divorced MAF - over in the air intake duct by the air filter box. ANY air leak at the MAF or intake ducting - hose itself or clamps - will screw up fuel mixtures. If there's a sort of resonator box stuck into the air intake duct, if that's not perfectly sealed at the spigot, that will cause problems, too.

Unhooking the battery accomplishes nothing. Most of the modules in this car, including the PCM, have long-term internal memory power supplies (lithium battery).

Crank sensors usually give a slow speed or coastdown engine stall, and once in a while, a slow speed stall at transition to open loop emissions operation - 160 degrees coolant temp. Look for DTC P0335/6 or P0385/6 along with a "stall detected" code.

brooksbronco82
12-29-10, 11:55 PM
That engine has a divorced MAF - over in the air intake duct by the air filter box. ANY air leak at the MAF or intake ducting - hose itself or clamps - will screw up fuel mixtures. If there's a sort of resonator box stuck into the air intake duct, if that's not perfectly sealed at the spigot, that will cause problems, too.

Unhooking the battery accomplishes nothing. Most of the modules in this car, including the PCM, have long-term internal memory power supplies (lithium battery).

Crank sensors usually give a slow speed or coastdown engine stall, and once in a while, a slow speed stall at transition to open loop emissions operation - 160 degrees coolant temp. Look for DTC P0335/6 or P0385/6 along with a "stall detected" code.

Thanks for the reply, I understand what your saying about the MAF sensor and tightened all clamps down tight. As for the resonator box I don't believe this car has that. The duct going from the filter to the TB doesn't have anything attached to it. I've read about it a few times on here and it's not there. No hole for it either.

Yeah the battery thing was a shot in the dark and really didn't think it would do anything but I've yet to test it. :suspense:

The symptoms that your describing for crank sensors going bad are interesting. It does stall sometimes when going slow and coasting to a stop. But no Codes for it at all. Car is completely undriveable as it is and will try to keep this updated in case it can help someone else.

Submariner409
12-30-10, 11:17 AM
Have you removed and cleaned the EGR valve and port ? A sticky EGR will cause all sorts of low speed performance problems.

Check that EVAP for leaks, too...............

brooksbronco82
12-30-10, 02:37 PM
Will pull the EGR off today and see what it looks like

brooksbronco82
12-31-10, 05:29 PM
Pulled EGR, valve moved smoothly and was not stuck. Ports were open and looked like they had a little carbon but that's to be expected. Wish I had a plate to cover the EGR ports to eliminate the solenoid.

I've unplugged MAP and MAF to maybe eliminate the sensors reading wrong and it still does it. Sprayed brake clean around intake and vacuum lines and watched fuel trims not seeing a change.

I pulled the line off the EVAP and put a rubber cap on it to eliminate the line. Car still does the same thing. I'm at the point where only crank sensors make sense. Stalls at least once now when I drive it around.

Submariner409
12-31-10, 07:42 PM
When all your diagnosis and testing by eliminating sensors/valves is done, it all has to be returned to stock configuration. Case in point: remove and/or cap the EGR and you can't believe the driveability problems you'll cause.

Very surprised you haven't set the SES light/message or gotten a slew of DTC's so far.........

brooksbronco82
01-03-11, 05:49 PM
Is there any way fuel pressure is part of the trouble? I just put a guage on and got 36 psi KOEO and idling. No way to look at the guage while moving but this seems low to me. I changed the fuel filter about 2 months ago. Surely It's not clogged yet but I have put in some injector cleaner so I guess it's possible. Possible failing fuel pump?

I just got the crank sensors but have not put them in yet.

Thanks for all the help.

brooksbronco82
01-03-11, 08:54 PM
Cleared codes then went for a short 2 mile drive and here is what I got ( haven't put the Crank sensors in yet )

B0429 current
P0101 current
C0660 current

The P0101 MAF code is still there but I feel like I've looked everywhere for a possible leak. There is a hiss that I hear from the power steering pump area but the sound changes when I remove the cap so I think it's from the power steering. I might try spraying in that area and under where the PCV line goes in the Intake again.

Could the stalling of the engine cause the P0101 and not be related to the true cause of my running problem?

Ranger
01-04-11, 12:03 AM
That fuel pressure is a little below spec's, but I'm not sure if it is low enough to cause a problem. To tell for sure you should really tape it to the windshield and see what happens when you throttle up. P0101 (Mass Air Flow (MAF) Sensor Performance) leads me to think the MAF sensor is bad. Did you replace it?

brooksbronco82
01-04-11, 03:41 PM
No I have not replaced it. I did unplug it and it still acted the same way. Not sure if this is good enough to rule out the sensor though.

brooksbronco82
01-06-11, 02:08 PM
Well I have replaced the crank sensors and that seemed to fix my bucking issues.

It's still not running 100% though.

It feels like it's very low on power with no get up now. When I unplug the MAP it seems to get better. The MAP is reading 10 in at idle but when i'm in gear and driving it goes up to 24 in at about 1600 RPMs. Do these numbers seem off to anyone?