Just completed a 4,000 mile journey...the coach lurched the whole way!

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rgnprof

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I have posted on this problem before (see the following thread - http://www.rvforum.net/SMF_forum/index.php?topic=43327.0).

Replaced the catalytic converter before we left - have also replaced the fuel pump and filter, all new ignition stuff, including the module, cap, rotor, wires, plugs, new air filter...

We went to Glacier NP and had a great trip - mostly stayed in state parks along the way.  The coach continued to lurch/surge some the entire trip!  Only on acceleration, under load and seems worse at lower speeds.  Cruised along just fine at highway speeds, unless I had to step on the gas pedal.  If I could hold the accelerator pedal steady - even up an 8% grade, once the tranny shifted in 2nd gear, it ran smoothly.  The lurching is definitely related to the throttle - even coming down a hill - if I press on the gas it would lurch some.  I kept pretty good gas records and we averaged between 8-9 mpg - usually driving between 60-65 (except coming home thru KS and OK, heading in to a strong headwind and running the genny the whole time - got about 6 mpg).  So, I can't see it being fuel related as I think 8-9 mpg is pretty good for my '93 Cobra Passport with an EFI 460 motor. 

It was just somewhat annoying, but you learn how to drive the thing to minimize the occurrence of the problem, but I plan on figuring it out - at some point!  I am thinking vacuum related, or TPS.  Another interesting observation is a slightly rough idle - especially when hot, and in drive.  Drop it in neutral and it idles smoother...

If anyone has any ideas, or suggestions - let me hear them!  Thanks.

ryan
 
check your air filter cover, I had an problem like yours and it was the fabric on the air filter cover that would partically cut off the air flow whenever I hit the gas  ( air flow sucked it down ).. took quite a while and a few guys to finlally find the problem
Good luck
 
It sounds like a lean condition. Check the EGR and all sensors. this new gasoline is trouble. It has too much oxygen and boils to low. Might try insulating the fuel line to keep it cool.
 
One of the first things I checked was the EGR - took it off, cleaned out the port, tested it and it seems to be working fine.  No codes are being set either...I'm not sure what you mean about the 'air filter cover'...my 460 motor has the air filter box under the hood, right in front - don't know for sure what you mean by a cover???

Again, my thinking is - if it was fuel related, wouldn't my mileage have been more effected?

I have asked locally - alot!  No one seems to be able to track this down....

ryan
 
Have you taken an analog meter and checked the TP sensor. At closed throttle to wide open throttle you should have a smooth swing of the needle. You may need to open and close the throttle several times to make sure you are not getting any errattic movement of the needle.
 
Be sure ECM is grounded to Chassis, to coach to engine. I have had this one stump me for months only to have my son tell me. Always check your grounds Dad!
 
Let me provide an update...

i have changed out the TPS - with some improvement, but I'm not sure...

I have gone back to checking fuel pressures per the advice from another forum.  I finally got around to driving the coach with a fuel pressure gauge connected...I had 34 PSI at KOEO, 28 PSI at idle and 38 PSI with vacuum hose pulled from fuel pressure regulator. While driving the coach at highway speeds I am getting 36ish PSI at WOT - doesn't really fluctuate much even when the coach starts its lurching under acceleration...the needle flutters rapidly. 

I changed the fuel pressure regulator - had an ACDelco spare, but I don't think it is helping.  KOEO PSI at 32 and falls to 30 - at idle it is still 28 and with hose off it is still 38. 

I am thinking - upon the advice of others - that I have a fuel pressure problem.  Local dealer believes that pressures under WOT conditions (vacuum hose removed from pressure regulator) should be between 45-50 PSI. 

If you remember, I recently installed a brand new Motorcraft PSF46 fuel pump, new fuel filter - so I don't know what's going on.  Unless, of course, I keep replacing bad old parts with bad new parts!

ryan
 
Fuel pressure at WOT should be higher and the needle should be steady. If I remember correctly, you changed the fuel filter before. It does sound like you have a restriction somewhere in the supply line. If it was in the return line you would see high pressure all the time. I am thinking you may have a fuel flow problem. I wonder if somthing hasn't pinched a fuel line somewhere.
 
I'm not sure how to go about finding a restriction...most of the supply line is steel and I can not find any obvious visible signs of damage or collapse.  I am thinking of pulling the fuel pump - again - and blowing compressed air thru the lines and might pull the filter again and see what it look like (I have changed the fuel filter twice since I bought the coach last August).  The dealer suggested blowing compressed air back through the lines in to the tank - maybe it would clear any restriction from the sock filter on the bottom of the pump assembly.  He also suggested pinching off the fuel return line and see what happens to the pressures...

BTW, Amazon sent me another fuel pump today, so I have another new pump that I will probably install if I can't find any other problems.
 
Your service manual should give the minimum required flow for proper operation in Gallons Per Hour.  My Chevy 454 with throttle body injection requires 25 GPH.  You can get a graduated container of some kind, remove the feed hose from the inlet to the EFI rail or throttle body and make it pump into the container.  Time how long it takes to fill it to a known quantity (like half a gallon or a gallon) and calculate the flow in GPH to see if it meets spec.  Most likely you will have to jump a relay somewhere to cause the fuel pump to stay on long enough to do this test and the service manual should cover how to do so.  The dealer should be well equipped to perform such a test if they have not already, I'm guessing since they are suggesting blowing air down the line that they may not be following much in the way of a troubleshooting protocol.

The specification for pressure at the rail should also be in your service manual and if the dealer says 45-50 PSI I would assume thats where they are getting it from.

On my ford truck I had a problem with erratic idle and surging while under load which sounds similar to what you are seeing.  It turned out to be a worn out and loose timing advance mechanism and worn distributor shaft so that might be something to look at as well.  I replaced the distributor and it took care of the problem.

Troubleshooting these early EFI systems is kind of a pain!  With ODB-II it became easy to see TPS readings, fuel pressures, etc...
 
I would love to find a service manual for this thing!  Dealers only have stuff back 10 years...so I have no idea of actual specs. 

Would Alldata or Mitchell's have this info?

It could be electrical, but I don't want to go gown that road if 36 PSI is too low...
 
Alldata or Mitchell will have the specs. You can pinch off the return line and see if the pump is capable of developing the pressure Is your pump in the tank?  If not you may very well have a partially blocked screen on the tank pick-up. I don't remember what years but some of the early ford fuel injection models used 2 pumps but if I remember correctly the sympton for a bad lift pump was hard starting.
 
Even a Chiltons manual probably has the flow and pressure specs and most likely a flow test procedure.  You might watch ebay for factory service manuals, they turn up from time to time.  Right now the oldest I see is 98, but I found an original factory manual for my 68 fork F250 that way, just kept searching every few days till one turned up.

What kind of injection does it have, throttle body or multi point?  Throttle body systems typically are lower pressure than multi point.
 
I am right now trying to figure out what to do about these pressure readings before I move to electrical/ignition stuff. Haynes indicates an engine running fuel pressure of 30-45 psi and Alldata says 30-40 psi - no real mention of what it should be at WOT.  I just checked pressures with the return line pinched off - at KOEO 34 psi and at idle 65 psi, with a fluttering needle.

This is a multiport EFI...
 
65 with the fuel return line indicates the pump is capable of achieving the pressure so you need to go back to the possibilirty of a reastriction in the line. Did you replace the fuel pressure regulator?  It could be bad.
 
Yea, I had a spare ACDelco pressure regulator, so I swapped it out.  Don't think it made any difference and actually I have noticed with this new regulator that pressure drops slowly with KOEO - starts at 34 psi and drops slowly over the next few minutes.  Once I shut the motor off, the pressure holds for quite a while.

I can not find any fuel line issues that are visible...
 
If you get 65 PSI with the return pinched off, the pump seems like it can make pressure, and the reading you are seeing seem within specification.  Anything under the pinched line pressure is due to the regulator.  Wonder why the dealer is quoting a higher pressure?  I would think the pressure should remain the same across the operating range of RPM and is probably why they don't quote different values for WOT.  The computer is going to be assuming a certain amount of flow from the injectors for a particular pulse width and that requires the pressure to remain about the same at any RPM.

Flow would be the thing to check next to see if there are any restrictions. If you can't find a spec for the amount of flow, engines typically require .5 lbs/hr per horsepower.  Fuel weighs about 6.2 lbs/gallon.  For the 25 GPH that my Chevy is speced at, it should be good for as much as 310 HP of engine output.  Of course the engine puts out significantly less power than that, so there is a large margin built in.  If you are getting at least 20 GPH (42 oz / min) I would think that would be sufficient to rule out a restriction in the lines.  The trouble with doing this check is finding the fuel pump relay and knowing what terminals to jump so it stays on long enough to get a reasonable run.  I would think that if the WOT pressure is within the 30-40 PSI per the spec that the flow isn't a problem.  Low flow at high delivery rates should translate into low pressure.

If the thinking is that it is a lean condition, have you tried pulling the plugs and taking a look at their color?  That should give you an idea if it is really running lean and if the various cylinders are all running with similar conditions or if some are much more lean than others.
 
Good advice to check the plugs for a lean condition but you need to go out and run it till it starts surging again and then check the plugs. WHen yhou were at 65PSI, even though the computer controls the pulse width based on ionfo from the )2 sensor and other sensors, you had a temporary rich condition which would show a rich condition on the plugs. 1992 was not particularly a good year for getting info from the computer so you will not get much help there with a scan tool. Are you Multiport or Throttle Body Injection?  No matter what it sure sounds like you may have a flow problem.When they changed the it could have been set a little richer than the one that was on there. They are normally set for .05V at closed throttle up to 2.0V at WOT.
 
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