Can bad EGR cause trnsmission problems?

[haydoracin]

I have the MH listed in my signature i.e. Chevy 454 P series with I believe the 4L80E transmission. Recently experienced problem with not shifting into overdrive and intermittent Check Engine light. OBD scan shows bad EGR valve. Could this cause the shifting problem?

[allbrandauto]

I fully understand how the system works the leak at idle I'm talking about is when the pintal sticks open at idle caused by carbon build up or carbon in the seat causing the valve not to close anyway the op is trying to find out why the trans. wont go into high gear

[enblethen]

double post

[enblethen]

You can read codes yourself.
How to read code
Doubt if it is EGR!

[j-d]

This 1994 P30 should be OBD1. How were the codes pulled and what were they? This Listing
shows several EGR codes. Hopefully replacing EGR will clear any/all of them.

Notice there is a Vehicle Speed Sensor (VSS) and it too can throw a code.

I mention VSS because some automatic transmissions of this vintage would shift 1-2-3 but not into OD/4 if VSS had failed.

[ScottG]

Deleted - entered in error.

[ScottG]

I'm sorry but my experience indicates you are wrong. You also don't entirely understand how the EGR system works.
There IS NO EGR present at idle - no vac is applied at the EGR valve, therefore a leak will not make it idle rough. It will not run rough going down the road either because of the raised RPM's. You can verify this by disconnecting any small vacuum line and driving - the eng will run smooth enough at higher RPM's (than idle) that you wont suspect anything is wrong.
I've had experience with several failing EGR's and none made it run rough.
If the valve itself is sticking, it will result in power loss but that is rare.

allbrandauto wrote:

ScottG wrote:

allbrandauto wrote:
A egr valve that has a vacuum leak will give you rough idle when you go down the road the egr valve opens up letting exhust into the intake to get rid of a gas called nox don't think this is your problem again cat. converter can cause this but you would also have no power is it not going into high gear or is the torque converter not locking up if its the torque converter not locking up could be brake light switch

It wont always give a rough idle.
Vacuum is only applied under certain throttle conditions (not at idle) and with the throttle closed, the engine will idle perfectly unless the EGR valve is stuck open - that is the only time it will cause a rough idle and that failure mode is rare. The usual failure mode of an EGR is that the vacuum diaghram gets ruptured. Then the vavle doesn't respond properly. Then at intermediate throttle positions, you will have a vacuum leak because the ECM is trying to apply vacuum to it and it's leaking.

[MEXICOWANDERER]

It appears this transmission uses a vacuum modulator. A leak or a bad modulator itself will cause shift issues. Can shift issues interfere with the transmission going into overdrive?

Diagnostics may want to include taking vacuum readings at the EGR valve and at the modulator vacuum line connection. Correct vacuum signals eliminate the chance of a vacuum leak causing the problem but do not eliminate the possibility of having a bad modulator itself.

A pro-grade OBD scan might be wise. The above is just a hint about receiving confusing OBD scan results - where to look next.

[allbrandauto]

yes you are right but vacuum leak is so minor it wont cause a driveabilty problem

[allbrandauto]

ScottG wrote:

allbrandauto wrote:
A egr valve that has a vacuum leak will give you rough idle when you go down the road the egr valve opens up letting exhust into the intake to get rid of a gas called nox don't think this is your problem again cat. converter can cause this but you would also have no power is it not going into high gear or is the torque converter not locking up if its the torque converter not locking up could be brake light switch

It wont always give a rough idle.
Vacuum is only applied under certain throttle conditions (not at idle) and with the throttle closed, the engine will idle perfectly unless the EGR valve is stuck open - that is the only time it will cause a rough idle and that failure mode is rare. The usual failure mode of an EGR is that the vacuum diaghram gets ruptured. Then the vavle doesn't respond properly. Then at intermediate throttle positions, you will have a vacuum leak because the ECM is trying to apply vacuum to it and it's leaking.

[ScottG]

allbrandauto wrote:
A egr valve that has a vacuum leak will give you rough idle when you go down the road the egr valve opens up letting exhust into the intake to get rid of a gas called nox don't think this is your problem again cat. converter can cause this but you would also have no power is it not going into high gear or is the torque converter not locking up if its the torque converter not locking up could be brake light switch

It wont always give a rough idle.
Vacuum is only applied under certain throttle conditions (not at idle) and with the throttle closed, the engine will idle perfectly unless the EGR valve is stuck open - that is the only time it will cause a rough idle and that failure mode is rare. The usual failure mode of an EGR is that the vacuum diaghram gets ruptured. Then the vavle doesn't respond properly. Then at intermediate throttle positions, you will have a vacuum leak because the ECM is trying to apply vacuum to it and it's leaking.

[allbrandauto]

A egr valve that has a vacuum leak will give you rough idle when you go down the road the egr valve opens up letting exhust into the intake to get rid of a gas called nox don't think this is your problem again cat. converter can cause this but you would also have no power is it not going into high gear or is the torque converter not locking up if its the torque converter not locking up could be brake light switch

[haydoracin]

Thanks for the responses. EGR will be replaced this afternoon. On another forum throttle position sensor was also mentioned as a possible cure.

[time2roll]

I would fix the EGR before you take it to the transmission shop.

[wnjj]

With EGR problems you may have had your foot harder into the pedal, making up shifts unlikely.

[TurnThePage]

I've had EGR issues which turned into catalytic converter issues which then reduced engine power, resulting in inability to hold a higher gear...