Hi,

I have a 4-speed automatic transmission in my 85 Firebird with the MPFI 2.8 litre V6. What transmission do I have? (I'm guessing a 200-4R.) And what are my options for replacing it?

As soon as I hit highway speed the other day, the transmission started hunting between 3rd and 4th gears. The next thing I knew, I couldn't go more than 50 mph: pressing harder on the gas made me lose speed, backing off allowed an upshift and I could then maintain speed.

When I got to my destination, I put the car in Park, in which case I could rev the engine. When I was driving, I couldn't throttle without the engine bogging down. Anybody familliar with these symptoms.

Jason

 

Its a 700R4

 

Sounds like fuel delivery.... almost certainly it's not the trans. It's hunting for gears because the engine is almost dying from lack of fuel.

Start with a new fuel filter. Proceed from there. Could be the fuel pump.

 

Fuel filter changed: no difference.
Disconnected MAF sensor: no difference.
Checked timing (11 degrees or so).
No codes stored in ECM after several short to medium trips.
EGR valve does not leak and moves freely.

I plan to check the fuel pressure next. Any tips for that, or any other suggestions?

The engine will bog down under load. I can rev the engine fairly freely when in Park, although there too, the engine can't rev as high as it should.

 

Spark plugs still working? Broken wires maybe?

 

sounds like the typical failing fuel pump....sometimes they just die, but sometimes ive seen them just loose presure....

 

> sounds like the typical failing fuel pump....sometimes they just die, but sometimes ive seen them just loose presure....

That's interesting. I've experienced a failing fuel pump, but it was a mechanical one. It gave a tugging sensation; you'd be driving along and then you would experience a MOMENTARY loss of power, like half a second. These losses of power would become a little more frequent until one day the pump would outright quit.

This pump IS a little noisey, but I didn't suspect it because the previous owner changed it in the last couple of years. We'll see once I get my hands on a fuel pressure tester.

BTW, the TPS was fully tested and is OK.

 

Tested fuel pressure with an Actron CP7818.

46 PSI at idle and vacuum hose disconnected from fuel pressure regulator.
Pressure dips a smidgeon for a fraction of a second as I stab the gas pedal.
46 PSI at a variety of steady engine speeds (4000 RPM +).
38 PSI at idle with vacuum hose CONNECTED to fuel pressure regulator.
46 PSI at higher RPM with vacuum hose CONNECTED to fuel pressure regulator.
46 PSI under load: car in drive, left foot firmly on brake, and right foot giving gas to about 1500 RPM.
Ignition ON, engine OFF, fuel system pressurized to 42 PSI and crept down to 35 PSI after 4 minutes.

What's next?

 

Checking the fuel pressure while it's actually malfunctioning.

 

I'm continuing this thread here: Car can't go above 50 mph

I feel that the title of the thread isn't appropriate, and neither is the message board: at first I was convinced that I had a transmission problem.

 

I drove around town with the fuel gage sticking out from under the hood just over my windshield so I could see it while driving. Fuel pressure was OK while the engine was bogging down. So the pump is good.

The problem ended up being a blocked catalytic converter.