Hi All,
New member here. I have a 4wd 1991 F350 with a 460 efi and auto transmission. It is a retired water company truck that I bought with 95k miles and I put around 1000 miles a year on it.

I have had a few minor problems over the years (sticking caliper, Torque convertor burping out fluid when hot, leaky fuel injectors) but it has been a good reliable truck overall.

I run all my other vehicles on CNG (natural gas) using a sequential injection system that interrupts the signal from the stock ecu to the injector, modifies it and sends it to the CNG injector.

There is a bit of a learning curve to getting the piggybacked CNG ecu calibrated but I have done ok with my Tundra and 4runner.

The F350 has been a real challenge. When I first installed the system it was responding to changes in the piggybacked cng ecu in a predictable manner and I was making progress getting it all dialed in.

I ran into some challenges with leaky gasoline injectors richening the mixture in a few of the cylinders while running on CNG. Once I got that sorted out the truck responded to changes in the CNG fuel map in a very predictable manner.

After making a few test runs I parked the truck and while still idling it felt as if a solenoid opened or something switched on or off and the truck suddenly started idling very rich. (I have an innovate motorsports wide band afr on it).

I started throwing parts at it IAC, map sensor, plugs, wires, new distributor, TFI ignition module on fender well. I did pay attention to ignition wire routing but could probable better understand the crossfiring issues than I do now. I checked the voltage at the coolant temp sensor as the truck warmed up and as I recall the voltage corresponded to the temp as it should.

I replaced the o2 sensor as well as trying to use the analog output from the Innovate Motorsports wide band o2.

I have had the truck running poorly on CNG for some time now and continue to tinker with it and cannot seem to diagnose the cause of rich idle on CNG.

If I switch to gasoline the mixture goes to somewhere close to 14.7. If I switch to CNG it moves to something like 12:1. Regardless of how I adjust the CNG ecu to modify the gasoline injector pulse width it seems like the ford gasoline ecu compensates and sets the mixture very rich. I might get a few seconds of appropriate mixture at idle on CNG before it goes back to a rich idle.

I have the fuel map fairly accurate on CNG (according to the wide band afr) at driving speeds.

The other problem I am noticing is the engine rpm, as indicated on an oscilloscope display included in the CNG tuning program on the laptop, has erratic spikes. It is not noticeable by seat of the pants or by ear but the line on the display indicating rpm is not a steady smooth output. It has a bump or a spike every few seconds.
This problem was much worse before I replaced all the ignition components. The truck would buck and stumble terribly on CNG (which needs a stronger spark) and at that point also noticeably on gasoline.

I do have an obd1 code reader and last I checked had no error codes which does not surprise me as it runs great on gasoline.

One of my theories is that I have a weak ignition system and it is not fully igniting the CNG air mixture and the resulting unburned fuel shows up on the wide band afr.

I have experimented with both stock plug gap .045 and closing the gap to
.035 (as is recommended on many propane/cng tuning forums)

The problem with this theory is the idle gets a little lumpy and "feels" rich to the point that I start to think it may really be getting to much fuel.

Tuning the Tundra and 4runner were a lot easier as I can monitor my fuel trims while making adjustments.

At this point I am open to suggestions.

In particular I am interested in:

ideas on testing/improving the ignition system.

Should I continue running autolite stock plugs or switch to something like NGK.

Better understanding the EGR system and how it might play a role.

Better understanding the Ford EFI used in this era

Is there anyway to monitor the fuel trims with obd1

Understanding how to identify the correct part #'s for a junkyard ECU that I could swap in to see if I have a failing ECU.

Are there any potential bad grounding points that might be causing the blips on my rpm displayed on the laptop scope.


The most puzzling part of this whole process is that when it started my buddy and I had just taken a few "1/4 mile runs" on a private road with him monitoring the laptop. We were both ready to give each other a high five it ran so strong and smooth and then we both felt a sudden change in idle (like a solenoid opened) and it has run rich at idle ever since. It was after this that I changed out all the ignition components.

If there are any existing threads that might guide me through a lot of this please mention any specific search terms I should use or specific forum members posts I should focus on.

Thanks for any input.

Karl

 

Others systems like propane I have looked at cut off the fuel from the tank while on propane. It does not sound like your CNG kit does that.

No fuel solenoid or fuel pump disable?
Does CNG use a little gas while on CNG?

 

This gaseous fuel system has the fuel pump running whether it is running on gasoline or gaseous fuel. In my case it is cng but by switching the regulator and recalibrating the fuel map it could just as easily run propane.

I can also switch individual cylinders from gasoline to cng if I have my laptop plugged in. This is how I discovered two of the gasoline injectors were leaking fuel into the manifold when they were supposed to be shut off.

I sent the injectors off to witch hunter performance to get them cleaned and flow tested.

I want to think it is an ignition problem but I am really puzzled by the fact that it went from relatively smooth idle to this rich lumpy idle at a very specific moment and has continued to run rich since.

I have read a handful of posts that mention this engine may not run in closed loop operation much of the time. This is difficult for me to imagine and it leads me to think I need to get a better understanding of the way ford set up their fuel injection before doing much more brainstorming.

I initially thought if I could find a diagnostic tool that would give me the fuel trims it would help me understand if I had my natural gas fuel map set up properly or if the ford ecu is having to make major corrections for my imprecise fuel map.

Does the fuel injection system operate in closed loop system under cruise and heavy load conditions?
Any suggestion on some good reading material specific to what ford is doing in this era of fuel injection?

Here is a link to a pretty thorough discussion of installing a kit like mine on a supercharged jaguar.
LPG Discussion Forum • View topic - DIY 2002 Daimler Super V8 (Jaguar XJR, X308 type)
It give a much better picture of the components and installation than I could do.

Thanks for replying,
Karl

 

If you have not done so remove the EEC and inspect it for exploded capacitors, electrolytics of this age are very prone to breadown.
The thing that your symptoms remind me of is a problem I had that was a result of the EEC losing keep alive power(pin 1), it needs that to retain changes it has made to fuel trims as it fine tunes to the engine, if if it loses those it has to start from scratch and rebuild trims at every start which will result in erratic behaviour. In my case the wire for pin 1 had corroded off at the EEC power relay.

 

Thanks for the idea on the EEC. I will take a look at it tomorrow and see if there are any signs of damage or corrosion.

I took a look at Oldfuelinjection.com and found a list of eec-iv that were installed on the 7.5 motor

<table bgcolor="ffffff" border="1" cellpadding="2" cellspacing="1"><tbody><tr><td>8SE</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank</td></tr><tr><td>DAD</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank</td></tr><tr><td>J2C1</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank</td></tr><tr><td>MOT</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank, C6</td></tr><tr><td>RUB0</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank / E4OD</td></tr><tr><td>W2T</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank</td></tr><tr><td>Z2Z</td><td>7.5</td><td>F-x50 E-x50</td><td>SD-Bank / Manual</td></tr></tbody></table>It looks like I can only use one with the code RUB0 if I have an e4od transmission. I may look around at pick n pull and see if I can find one or two.

I also found a chart describing when the eec goes into closed loop operation and if this chart applies to the 460/7.5 engine then it does operate most of the time in closed loop.

It looks like warm idle runs in open loop with "preset enriched values". If this is the case I can't understand why the eec appears to be modifying the injector pulse width richer for CNG operation. I will have to revisit the injector pulse width modification at idle and confirm I am not misinterpreting things.
The other thing I just noticed that may be a problem is the ignition timing gets retarded 1 degree at warm idle after 1 minute. CNG wants more timing advance as its high octane slows the burn rate down. Maybe this shift in timing advance is complicating my attempts to tune the idle mixture.

I am not sure what I was reading that made me think some claim the 460 efi engine rarely runs in closed loop.

I am still needing to figure out if it is possible to monitor fuel trims while on the road to dial in my cng fuel map.


<table align="center" bgcolor="#E8E8E8" border="1" width="744"><tbody><tr><td width="135">Strategy
</td> <td width="150"> Fuel
Control
</td> <td width="150"> Spark
Control
</td> <td width="125"> Emissions
</td> <td width="150"> Sensors
in Use
</td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> None
</td> <td width="150"> </td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> </td> <td width="150"> </td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> </td> <td width="150"> </td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> </td> <td width="150"> </td> </tr> <tr> <td width="135"> Warm Cruise
</td> <td width="150"> Closed loop: 14.7:1
</td> <td width="150"> RPM vs Load Multiplier
ECT Multiplier
EGR Multiplier
</td> <td width="125"> EGR
Canister Purge
Air to CAT
</td> <td width="150"> RPM / MAF or MAP / TPS / ECT / ACT / EGR / HEGO
</td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> </td> <td width="150"> </td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> None
</td> <td width="150"> </td> </tr> <tr> <td width="135"> </td> <td width="150"> </td> <td width="150"> </td> <td width="125"> </td> <td width="150"> </td></tr></tbody></table>

Thanks for the ongoing input.

Karl

 

The 460 that I have very seldom goes into closed loop. The only time it goes into closed loop is when you back out of the throttle at highway speed and going down hills with a warm engine.

I do not have much information on a 1991 EEC-IV system but the 1994 EEC-IV 460 that I have has a data output that you can monitor if it is in closed or open loop. I do not know what years and engine types had the data output at the self-test connector but it looks like the 1992 F-series did have it.

Example of my 1994 460 output:


/

 

You may also want to read this thread and may be what you have read about the open and closed loops:
http://www.irv2.com/forums/f23/1996-...oop-92794.html
/

 

Your engine data copied in to your last post along with the link lead me to conclude that what I read in oldfuelinjection.com does not apply to the 460.

I am getting the impression that this particular engine more or less has a preset fuel map that it runs on and in very limited conditions it may go into closed loop.

If I am understanding it correctly it seems like I don't have much to gain by checking out the EEC. I will just for the heck of it but it seems like it just follows a preset fuel map which is modified based on temp, tps, rpm and map.

This might explain some of my challenges getting my CNG fuel map dialed in. I got somewhat spoiled setting up the Toyotas on cng as the long term fuel trims can correct big errors in the fuel map surprisingly well. I will assume I can't count on the ford eec giving me this same benefit and need to get my fuel map as close as possible to perfect.

My idle mixture is the real issue I have been fighting and if I am correct in understanding that the timing retards 1 degree after idling for a minute that may explain some of the erratic behavior and rich idle mixture.

Retarding the timing on CNG would have the effect of sending unburnt fuel into the exhaust system as it would still be burning when the exhaust valve opens.

I just need to figure out why it seemed to run so well for a brief period after fixing the leaky gasoline injectors.

What do you use to record engine data from the eec?

Karl

 

I use the Actron Scanner CP9190 to read the OBD-1 data and it will also work on the OBD-2 systems.
I also use the Equus/Innova 3145 code reader if I just want to read codes as it faster to just get codes and easier to use.

Also I changed the link in post #7 above as this is the link I was wanting to let you read.

 

I am thinking I should recheck my ECT sensor and make sure my thermostat is getting the engine up to operating temp.

I only have the stock temperature gauge on the truck but the laptop interface for the CNG system tells me that after 10 minutes of operation the regulator (heated by engine coolant) is running at 60 degrees C/140 degrees f. This is a poor judge of actual engine temp as reported by the ECT sensor but it might be worth checking and could explain my rich idle.

Oldfuelinjection.com reports that ECT temps below 185 degrees will enrich the fuel mixture.

Still planning on checking the EEC as well, just couldn't fit it in this evening.

Karl

 

I still haven't checked the EEC for bad connections or components but I did replace the thermostat and the temp gauge indicates significantly higher and my natural gas regulator now runs at a consistent temp regardless of engine load.

At the same time I swapped out the autolite plugs for a set of ngk platinum plugs.

The idle is still rich but the acceleration has fewer stumbles off the line. At this point I should recalibrate my fuel maps since the operating temperature is totally different and this should be impacting the fuel injection parameters.

Another quirk that I can add to the puzzle is I can set each individual cylinder to run on either natural gas or gasoline. If I am idling on CNG and switch one cylinder at a time to gasoline I find the idle is smoother with cylinders 5 and 8 running on gasoline. CNG tends to be more difficult to ignite so I am assuming I am getting a weaker spark or possibly have a vacuum leak on those cylinders.

I have my plug wires routed across the distributor cap as is indicated on several 460 wire diagrams online. I don't know the exact route they should follow across the cylinder heads. I did find a very detailed routing for the 5.0 liter engine to prevent cross firing but can't find the same for the 460.
Should I be worrying about my precise wire path across the heads to prevent crossfiring?
I read references to a smoke machine for checking vacuum leaks. I need to learn more about this to see if I can rig something up to check for vacuum leaks on cylinders 5 and 8.

Any ideas are welcomed.

Karl

 

have you looked into a tweecer to help manage and stabilize ecu settings ? and also for data logging

 

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