Looking for some help - engine stumbling under load

Hi all,

I have been pulling my hair out with a 1990 E-350 Ford based RV. It has a 460 CID EFI engine.

The engine bucks and stumbles under load (in higher gears), usually between 35-45 MPH. However, it will sometimes buck and stumble at high rev (lower gears) such as when merging onto an interstate. Problem mostly seems to happen when the engine is warmed up.

Things I have replaced so far:

• Fuel filter
  EGR Valve
  EGR Valve Position Sensor
  EGR Valve Solenoid
  Coil
  Spark Plugs
  Spark Plug wires
  Distributor
  Ignition Control Module
  Engine Temperature Sensor
  Catalytic Converter
  In-tank fuel pump (about 4 years ago).
  Idle Air Valve
  MAP Sensor
  Fuel Pressure Regulator

The OEM FPR is running about 40 PSI idle, about 48 PSI under max load. I put it back in. I had replaced it with a new one and it was running about 30 PSI idle, about 38 PSI under load. There was no change in symptoms between the new one and the OEM one so I put the old one back in.

I bought a new computer, and part numbers match, but when I put it in the engine ran much worse. So I put the OEM computer back in. I exchanged the first computer for a new one, thinking it might be bad. I have not opened the box on the new computer yet as once you break the seal you can only return it for core fee.

Any ideas?
Steve

maillemaker wrote:Hi all,

I have been pulling my hair out with a 1990 E-350 Ford based RV.  It has a 460 CID EFI engine.

The engine bucks and stumbles under load (in higher gears), usually between 35-45 MPH.  However, it will sometimes buck and stumble at high rev (lower gears) such as when merging onto an interstate.  Problem mostly seems to happen when the engine is warmed up.

Things I have replaced so far:

• Fuel filter
  EGR Valve
  EGR Valve Position Sensor
  EGR Valve Solenoid
  Coil
  Spark Plugs
  Spark Plug wires
  Distributor
  Ignition Control Module
  Engine Temperature Sensor
  Catalytic Converter
  In-tank fuel pump (about 4 years ago).
  Idle Air Valve
  MAP Sensor
  Fuel Pressure Regulator
  

The OEM FPR is running about 40 PSI idle, about 48 PSI under max load.  I put it back in.  I had replaced it with a new one and it was running about 30 PSI idle, about 38 PSI under load.  There was no change in symptoms between the new one and the OEM one so I put the old one back in.

I bought a new computer, and part numbers match, but when I put it in the engine ran much worse.  So I put the OEM computer back in.  I exchanged the first computer for a new one, thinking it might be bad.  I have not opened the box on the new computer yet as once you break the seal you can only return it for core fee.

Any ideas?
Steve

I would simply start by removing and having the injectors tested and cleaned.

I would simply start by removing and having the injectors tested and cleaned.

I'm going to do that this weekend myself. I've got a tester that should be in today, and I'm going to pull them and blast them forwards and backwards with carb cleaner.

Do an ohms test on each one of them and check their values against the specs. One (or more), could be functioning fine in certain conditions, but could be weak when the duty cycle increases.
Just a thought.

I am not having any luck finding what the ohm spec should be for a 1990 Ford 460. I know that I can test each one (which I will) and look for the odd man out.

But it is not in my Chilton manual nor the shop manuals I have.

Thanks,
Steve

OK I found this:

https://www.trickflow.com/search/product-line/trick-flow-tfx-fuel-injectors/make/ford/injector-impedance/14-4-ohms/engine-size/7-5l-460

All of their listed 460 fuel injectors are 14.4 ohms.

Steve

Problem is fixed. It was the Air Charge Temperature Sensor.

Steve

Did it show a code for that?

No. Nor did it show a code when the Engine Temperature Sensor went out about 6 months ago and was idling poorly when cold.

Steve

So, the problem is not fixed.

So far, I have replaced the following:

• Fuel filter
  EGR Valve
  EGR Valve Position Sensor
  EGR Valve Solenoid
  Coil
  Spark Plugs
  Spark Plug wires
  Distributor
  Ignition Control Module
  Engine Temperature Sensor
  Air Charge Temperature Sensor
  Catalytic Converter
  In-tank fuel pump (about 4 years ago).
  Idle Air Valve
  MAP Sensor
  Fuel Pressure Regulator

I was about to give up and took the RV into my local Ford dealership today. They said they no longer have the manuals or tools to work on it, and their techs were not born when it was made (1990).

I have purchased a Ford Rotunda EEC-IV Monitor and Recorder device that will let me interrogate all of the inputs and outputs to and from the computer.

I tried to hook it up last weekend but the nose of the Monitor connector is just a hair too short and will not reach through the hole in the firewall to plug into the EEC. I have ordered an extension cable that should let me fish it through the firewall to reach the EEC in the passenger compartment and also the harness plug under the hood.

While messing around with the harness plug for the EEC I noticed a wire with worn insulation and exposed wiring. The wire was black. Unlike the rest of the wires that came right out of the plug and disappeared into the harness casing, this wire was wrapped around the other wires in the bundle and then disappeared into the casing. I had cut the wire and stripped the insulation, unwrapped it from around the bundle, and tugged on it lightly and it came out of the harness! At first I was like, "Oh crap, I just broke the wire down inside the harness!" But on examining the end that was tucked down in the harness it was cut perfectly smooth - deliberately. I now believe that this wire is simply an unused wire from the EEC plug and the excess was tucked down into the harness. I put shrink tubing over the exposed end from the plug and the engine runs as it always did, stumble and all.

The stumble happens at all power levels, but most consistently it happens when the transmission (E40D) is in top gear (4th gear), and you go up a slight hill and lug the engine at 45 MPH. It is when you lug right on the verge of the transmission downshifting that it will start to stumble. When the engine downshifts, it seems the stumble goes away, though it might just be masked by the high revs.

Someone has suggested shudder-chucking of the transmission but it feels like an engine miss, not a transmission issue. Someone said I can lightly press the brake while it is stumbling and this will disengage the AOD (4th gear) so I need to test that.

Any ideas?

maillemaker wrote:So, the problem is not fixed.

So far, I have replaced the following:

• Fuel filter
  EGR Valve
  EGR Valve Position Sensor
  EGR Valve Solenoid
  Coil
  Spark Plugs
  Spark Plug wires
  Distributor
  Ignition Control Module
  Engine Temperature Sensor
  Air Charge Temperature Sensor
  Catalytic Converter
  In-tank fuel pump (about 4 years ago).
  Idle Air Valve
  MAP Sensor
  Fuel Pressure Regulator
  

I was about to give up and took the RV into my local Ford dealership today.  They said they no longer have the manuals or tools to work on it, and their techs were not born when it was made (1990).

I have purchased a Ford Rotunda EEC-IV Monitor and Recorder device that will let me interrogate all of the inputs and outputs to and from the computer.

I tried to hook it up last weekend but the nose of the Monitor connector is just a hair too short and will not reach through the hole in the firewall to plug into the EEC.  I have ordered an extension cable that should let me fish it through the firewall to reach the EEC in the passenger compartment and also the harness plug under the hood.

While messing around with the harness plug for the EEC I noticed a wire with worn insulation and exposed wiring.  The wire was black.  Unlike the rest of the wires that came right out of the plug and disappeared into the harness casing, this wire was wrapped around the other wires in the bundle and then disappeared into the casing.  I had cut the wire and stripped the insulation, unwrapped it from around the bundle, and tugged on it lightly and it came out of the harness!  At first I was like, "Oh crap, I just broke the wire down inside the harness!"  But on examining the end that was tucked down in the harness it was cut perfectly smooth - deliberately.  I now believe that this wire is simply an unused wire from the EEC plug and the excess was tucked down into the harness.  I put shrink tubing over the exposed end from the plug and the engine runs as it always did, stumble and all.

The stumble happens at all power levels, but most consistently it happens when the transmission (E40D) is in top gear (4th gear), and you go up a slight hill and lug the engine at 45 MPH.  It is when you lug right on the verge of the transmission downshifting that it will start to stumble.  When the engine downshifts, it seems the stumble goes away, though it might just be masked by the high revs.

Someone has suggested shudder-chucking of the transmission but it feels like an engine miss, not a transmission issue.  Someone said I can lightly press the brake while it is stumbling and this will disengage the AOD (4th gear) so I need to test that.

Any ideas?

Does this transmission have a lockup converter?

It is an E40D, so I assume it does? I'm not sure.

Someone has suggested that I go test drive it and when it stumbles lightly tap the brake, which should disengage the lockup. When it stops raining I will try that.

Steve

try this pull apart all wire connectors related to engine, see if they are corroded. Clean them any way.

I am not entirely certain yet, but this may have been transmission shudder all along.

Today I took it for a test drive on my usual "test loop". Unfortunately I could barely get it to reproduce the problem. Most times it would not. Only a couple of times did I get the stumble. But when it did stumble, I tapped the brakes, and I could hear and feel the lockup drop out and the engine RPMs increase slightly. The stumble seemed to go away. I'm not entirely sure if they just faded out on their own, or if the increase in engine speed hid the miss.

Today I did a complete fluid replacement and the filter also. Afterwards I got no "stumble" at all.

Hi sounds like a timing issue.. how many miles on it?? check it with a light if it moves around while at a steady idle rpm the chain is bad..
good luck
tim

About 86K miles on it, but the distributor was replaced by my mechanic just a couple of months ago. It's possible they screwed up the timing, of course.

I'm not even sure how to check the timing on these vehicles. Something about disconnecting a SPOUT connector.

I picked up more Mercon V today so I can finish filling up the transmission, and I'll go for a test drive.

Steve

Tentatively, I believe I may have fixed the problem. It was not an engine miss at all, but the transmission.

Evidently there is an issue with E40D transmissions and the converter lock-up where sometimes this will cause "shudder". This is sometimes called "shudder chucking" or "trailer hitching".

My RV has close to 87K on it. I believe some years ago I had the transmission fluid filter replaced, but I don't think I did a full fluid change at that time. As it turns out, the service life of Mercon fluid is only 30K miles. So I'm coming up on 3 times that. So I did a complete fluid change by letting the system pump out the old fluid through the coolant line into a 5 gallon bucket while I periodically added more through the filler tube (basically when the bucket line starts showing bubbles it's time to add more down the filler tube.

I've gone on 2 test drives now, and cannot replicate the "stumble".

I've spent a lot of time and effort and money chasing down what I thought was an engine problem and it probably was not that all along.

They key to the diagnosis was to tap the brakes while the stumble was happening. This would disconnect the converter lock-up and the stumble would go away.

Good to hear that's why I asked above if it had a lock up converter as I thought maybe that could have been the problem!!