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rgnprof · 07-20-2011, 01:45 PM

Sorry this is long, but I have posted questions related to this issue in other RV forums - let me try to be thorough, but succinct as possible. I have a '93 Cobra Passport on a Ford E350 chassis with a 460 EFI motor, with 62,000 miles. The "first" problem was that the coach would just cut out after driving it for several hours (almost like it was vapor locking)- seemed to be worse when hot. After much reading and research, I troubleshot a bad fuel pump...

Replaced the fuel pump with an OEM Motorcraft pump and that problem has gone away. I also had the really loud, whirring idle speed control valve/motor problem and I replaced it with a BWD part and no more noise.

But, I have 'created' a new problem - the coach now lurches ONLY under load. Whenever I step on the gas - going up a hill, or even down a hill - the coach does not accelerate smoothly. If I back off the throttle some, it runs fine. Cruising at 65-70 on a straight flat stretch, it runs great! It also idles a little rough - more noticeably so when in gear...drop it in to neutral and idle evens out. I just returned from a 4000 mile trip and it did it the whole way - but other than that, I had no problems (even got between 8-9 mpg's). The engine has plenty of power - and even driving through the mountains in Wy and Montana it ran well. It would lurch slightly when the transmission dropped in to 2nd on the way up a steep grade, but once it started to even out up the hill, no lurching - would easily climb the steepest grades at 45, 50 55 mph. Generally, seems to run better with the OD off, and I had a friend suggest that the torque converter lock-up switch was not working properly. He suggested that when it did it again, touch the brakes while still accelerating and see if it stops lurching - tried that and it made no difference!

Here is what has been replaced:

1) Throttle position sensor (Motorcraft)
2) fuel pump and filter (Motorcraft)
3) idle speed control motor (Borg Warner)
4) ignition control module (fender mounted) (Motorcraft)
5) plugs (Motorcraft), wires (Belden from NAPA), cap, rotor (Autozone)
6) ignition coil (Motorcraft)
7) air filter
8) catalytic converter (Walker)

I changed the Transmission fluid at 60,000 miles and no particles - old fluid looked good. Other than this lurching on acceleration, coach runs great and I'm getting about as good gas mileage as can be expected! I have tried pulling codes several times and none are present - and I have troubleshot the EGR system and it seems to be functioning properly. The last thing I changed out was the TPS, and I really thought that was it - no such luck.

I have not checked the fuel pressure while running - I am down to a possible bad/weak NEW fuel pump, or possibly the in-tank strainer is clogged, or maybe a bad PIP sensor in the distributor. I really don't know...

Any advice? Thank for reading...

Ryan

subford · 07-20-2011, 02:47 PM

Sounds like lack of fuel.
Others have solved the problem by putting an in line fuel pump on the pressure line.
Here is a write up about it in the attached PDF at the bottom of this post. The first page and links I added to the PDF, so the PDF starts on the second page. This write up was for a F53 but an E350 would be about the same except the Inertia switch would be in a different place.

I redid the diagram a little for my F53:

rgnprof · 07-20-2011, 03:33 PM

Bill,

Thanks for your response - I have read many of your posts, so I appreciate your help. I have toyed with the extra fuel pump...my question is why did this just suddenly become a problem? This lurching issue only came up after I replaced the fuel pump and maybe specifically after replacing the Idle Speed Control Valve/Motor...It didn't do this for the first several months I owned it and I have had lengthy conversations with the PO (a friend) and this is a new problem. He did talk about having to replace the ABS sensor because of a lurching/shift issue, so I pulled the sensor and cleaned it off.

ryan

subford · 07-20-2011, 04:41 PM

As you noted that it sounds like a TPS sensor. As you know a TPS has three positions, CT, PT & OT.
When the engine is started the computer looks at the TPS and takes the value as CT. That is why you should not touch the throttle when starting the engine. This value should be less that 1.0 VDC and can be anywhere from 0.6V to 1.2 volts but 0.9V is what I like to see. If the math in the computer never gets to OT you may have a lack of fuel to the engine to air amount going in. If CT is 0.9V then OT should be >4.6V.

I do not think you can check the three throttle positions with a 1993 Computer. I think that started in 1994 in trucks and the F53 but I do not know about the Vans.

I would check the voltage on the TPS wire (back probe it) going back to the computer to see what it is. This wire may be open between the TPS and the computer.
You may have got a bad TPS. The EGR valve may be staying open too long also when you go to WOT.

You may want to go ahead and put a fuel pressure gauge on it and tape it to the mirror or onto the windshield. Then you would know for sure what is going on, that is what a Ford Dealer would do.

Topflite51 · 07-20-2011, 06:01 PM

Couple of WAGS:

1. Check the PCV hose and PCV system for integrity. Could be sucking air causing lean condition; or

2. Check emission evap system, could be plugged pullling vacuum.

Like I said, couple of WAGS.

spotknot · 07-20-2011, 07:35 PM

sounds like a vacum problem, may-be?

mpaton · 07-20-2011, 09:06 PM

I don't feel I have a good understanding of this "lurch" you have. Certainly not well enough to point the problem at the engine or the transmission.

Despite this, you don't mention checking for ECU codes. You have an OBD-1 system, and it can store codes without setting a check engine light. There are also tests you and the ECU can run (the KOEO, and KOER tests). It's possible to run these with a paper clip and counting light flashes but an Equus 3145 is only around $25 these days, and seems to make the test results more repeatable for many people.

Some of your symptoms could be transmission, and some EGR valve related. In any case, running the tests and checking codes is worth doing.

rgnprof · 07-20-2011, 10:29 PM

I do indicate toward the end of my first post checking for codes numerous times - I do have the Equus Ford Code reader, but I am not pulling any codes and I have no CEL.

The lurch is hard to describe - occurs only under load and it feels like the car is starving - for fuel or air... Acceleration is uneven and and lessens as I let up off the gas pedal. Maybe better called a stumble, maybe a sputtering....

Feels fuel or air related and seems to be related to the throttle position but I don't know...

I did know the TPS testing procedure, but it is a real pain on this van chassis to get to the TPS to backprobe the leads...decided to just replace the TPS for approximately $25.

I did have the vacuum system smoked and small leaks were noted at the Idle Speed control valve - which I thought was normal...

ryan

mpaton · 07-21-2011, 03:57 AM

Quote:

Originally Posted by rgnprof

I do indicate toward the end of my first post checking for codes numerous times - I do have the Equus Ford Code reader, but I am not pulling any codes and I have no CEL.

Indeed you did. My apologies. Interesting that the KOER tests had no codes. I had hoped they would have been more useful.

Quote:

Originally Posted by rgnprof

I did have the vacuum system smoked and small leaks were noted at the Idle Speed control valve - which I thought was normal...

ryan

I'm not sure what was detected here. The ECU sends an electrical signal to the idle Air Control Solenoid, so there is no vacuum line in the operation of the IAC actuator.
So was this small leak perhaps to do with another actuator?

rgnprof · 07-21-2011, 07:52 AM

I watched them perform this test and smoke was clearly leaking from the little black plastic 'cap' on the side of the Idle Speed Control Valve...my understanding was that this is normal? That it is a "controlled" vacuum leak, to stabilize the idle? Again, I'm not positive about how this valve works and it does seem that my problems started when this was replaced - but I don't see how this valve could have any thing to do with issues at wide open throttle...

ryan

subford · 07-21-2011, 08:05 AM

I do not see either but I do not think any smoke should have come out of it.

Also if the the computer does not see OT from the TPS it may not close the EGR valve.

The Idle Speed Control Valve:

/

rgnprof · 07-21-2011, 08:31 AM

Your picture does not include the black plastic cap as seen in the link below - I don't know what this 'cap' does...

Amazon.com: Motorcraft CX1665 Idle Air Control Motor: Automotive