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Gary
Gary, GMC Technician
Category: GM
Satisfied Customers: 15730
Experience:  15 years gm master tech/15 years ASE master tech
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2000 Chevy Malibu LS, 3.1L V6. Did a complete tuneup. AC

Customer Question

2000 Chevy Malibu LS, 3.1L V6. Did a complete tuneup. AC Platinum OEM Plugs gaped at .060, new pro quality wires, air filter, gas filter, PCV Valve, oil & filter change, coolant at the mark. Starts and runs and sounds nice, temp gauge in mid-range, no matter how long it runs. No warning lights in dash are lit, (Bulbs are all good) looks normal.
Problem: At exactly 3900 RPM the engine acts like it is rev limited, drops back to 3400 to 3500 RPM, revs right back up to 3900 and does this continually, as long as accelerator is held or even pushed further. It will run at 3800 RPM all day long, smooth as silk.
Removed the exhaust at the engine manifold to eliminate a possibly plugged Cat and no change except it sounds mean. Still precisely 3900 RPM.
At my wits end. Thanks in advance.
Submitted: 1 year ago.
Category: GM
Expert:  Gary replied 1 year ago.

I am sorry for the long wait

it will do this when driving down the road ?

or only in park and neutral ?

Customer: replied 1 year ago.
N.P. Driving, park and neutral
Expert:  Gary replied 1 year ago.

any idea what the fuel pressure is when it is doing this ?

was it doing this before all that work was done ?

Customer: replied 1 year ago.
It was doing that before all the work was done. Found out when trying to use the Cruise Control and it had to downshift on a hill. Of course the revs came up and kicked out and really, really confused the Cruise Control.
No idea what the fuel pressure is. Can check that, but don't know how quick, given that I have not done it before.
Expert:  Gary replied 1 year ago.

there is no time limit on this question

connect a fuel pressure gauge to the test port on the fuel rail end right behind the power steering pump and see what the fuel pressure is key ON engine OFF and also when its acting up

Customer: replied 1 year ago.
Okay-it will be awhile before I get back to you-about an hour.
Expert:  Gary replied 1 year ago.

ok

Customer: replied 1 year ago.
Okay I'm poorer now, but I own a nice fuel pressure gauge. Not running it reads 50 psi. Running idling it is 48 psi. At 4900 RPM it reads 48 psi. The fleas from a thousand camels on the people at GM, who put the PS steel tubing from the PS Pump, directly in front of the Fuel Rail test port. No, I wasn't drinking beer and eating dinner, but now I will.
Customer: replied 1 year ago.
Back tomorrow morning after 9 AM EST
Expert:  Gary replied 1 year ago.

sounds good

any access to a scan tool to see live computer data ?

Customer: replied 1 year ago.
A mix of Murphy's Law and Life getting in the way here. At the moment I do not have a scanner that works, due to a compatibility problem between Windows XP and Windows 8 on my laptop. I will make an effort to borrow my neighbor's Hand-Held, who unfortunately works graveyard shift and won't be home til mid afternoon. My daughter and I have appointments to have our hair cut about that time, some distance away, so it will likely be much later before I can tell you anything. There isn't anything showing on the dash, but there are bound to be stored codes from misfires, caused by me with the ignition coils. I might be able to get it down on the ground and drive it to my local parts store and have them do it. Will keep in touch, because I need this nice Malibu, 6000+ RPM capable, for an upcoming vacation on the 13th. Later.
Expert:  Gary replied 1 year ago.

sounds good

since the fuel pressure is good and the exhaust is not plugged up and the rev limiter is seeming to kick in which it should only in park and neutral i am curious if the computer is seeing the car in drive when it is in drive

if the computer see's neutral or park when it is in drive then that is our problem

but in drive it should not kick in and the rev limiter is built into the computer

Customer: replied 1 year ago.
Okay I used a good Scan Tool and it says Zero Codes, key on or when running. I am suspicious of nothing "stored". The battery cable being disconnected, in the recent past, may well have cleared any stored codes, but I am not any kind of expert on that.
I am beginning to believe the ECM is in "Limp Mode". I have never seen a car run so good in "Limp Mode", but then that was years ago. I read one article online, about a Lincoln ECM that was zapped by a voltage spike and caused it to be "Rev Limited" to 4000 RPM. There is only a slight difference between the two RPMs in this case, but it is the only straw I have seen, to grab for.
Customer: replied 1 year ago.
I will be back from time to time today.
Expert:  Gary replied 1 year ago.

if the computer is showing drive when in drive and the rev limiter is hitting there has to be a programming or internal computer failure happening to this car

Customer: replied 1 year ago.
Okay I agree. How do I test to see if the computer is being sent the signal, that the car is in Drive. I would think that that, would come from the gear selector switch on the tranny. Better yet, is the "In Drive" signal at the ECM's connector? I haven't even looked up where the ECM is hidden on this car. I have a Fluke 77 Multimeter and some Data Probes.
Expert:  Gary replied 1 year ago.

monitoring live computer data see if the live data matches the gear selection

if it does match try to have the computer re programmed if it still does this replace the computer

Customer: replied 1 year ago.
Ok thanks. Will let you know how this pans out.
Expert:  Gary replied 1 year ago.

sounds good