I'm in a bit of a pinch and need to get my truck diagnosed and fixed fast. I could really use your help! I've got '94 7.3 non-turbo old ambulance that I converted into a camper. I'm supposed to be using it to move/live out of as I travel across the country from NC to Seattle. My lease is up in 9 days and my truck just started acting up. I need to either fix it or scrap it and buy a new car FAST! All the diesel mechanics in town are way backed up and my lease is up on the 30th. Gonna have to do this on my own! Here's what's been going on.

1) Truck has no power under load. When accelerating quick on an on ramp, the engine revs high and sometimes won't shift unless I back off on the pedal. Going up hills it has very little power.

2) Poor throttle response. If I slam the pedal to the floor there is no response, like there's no extra fuel being sent to the engine.

3) Not sure if this might be related or not, but the tach has been working on and off since I bought the truck years ago. It seems to work better in the summer.

4) Problem began after heavy braking. Again not sure if it's related, but this issue started immediately after coming down a long windy steep hill during which time the brakes got real hot.

So far....
1) Initially thought it might be a simple fuel filter, but the truck also runs on veggie. When in veggie mode the truck uses a different diesel filter specifically designated for the veggie and bypasses the regular diesel filter. Problem exists in both veggie mode and diesel so I'm pretty sure it's not a filter issue. It has a brand new veggie filter.

2) Possible TPS sensor on side of IP. Disconnected harness and used multimeter to check for voltage change upon revving engine. I couldn't find a spec quickly so I just assumed that a change in voltage upon revving was enough to indicate a working sensor. Is this correct? I don't remember what is was, but it was very low. Less than a volt I think, but there was definitely a response when I revved.

3) Took it to a transmission guy and he assured me it was not a transmission issue.

4) Removed air filter. Problem persists.

I'm picking the truck up in the morning and need to get started working on it on my own. Any help would be GREATLY appreciated!

 

I'd put a new lift pump in it. $30 or so, easy fix.
Then, see what happens.

If that doesn't fix it(and it might), the next step is to get a quart of ATF. You'll empty your water seperator/filter(I'd replace it at the same time), fill it with ATF. Screw it back on, start the engine and let it idle for about 45 seconds. Shut it off and let it sit overnight.
Then, start it up, let it warm up and run it /hard/. The ATF should clean out some gunk/stickyness in the IP, if that's the problem... and if you're using SVO, it could easily be.

 

Thanks for the rapid response. I've got a neighbor taking me to pick the truck up at 9:30 tomorrow morning. I'll try those things first thing and repost ASAP. Just want to make sure I understand. You're saying to fill the entire diesel filter with ATF fluid and run it for 45 seconds to saturate the IP with ATF fluid?

 

Basically, yes. The truck will run on ATF, though it may smoke a bit. But ATF has some good detergent properties, which will tend to clean things for you.

 

For this purpose does brand or type of ATF matter, i.e. does Type "F" OR Mercon have more detergent than Texaco brand or Wal-Mart whatever?

 

Does your WVO system have its own fuel pump too? If not, you should. If not, I'm not sure how it uses the stock lift pump, but also bypasses the stock diesel filter.

Also, does your WVO system have steel or copper fuel lines? Or a steel tank? If not, you should be using rubber or aluminum hoses, aluminum fittings, and an aluminum or plastic tank. Copper and steel will cause polymerization which will allow flakes to build up in your IP and injectors. Hopefully the ATF will help clean that stuff out.

How does the WVO supply line splice into your stock system.... Does it have a selector valve after the stock diesel filter up to the input line to the IP?

If you have a separate fuel pump and separate filter head for the WVO side, and you are getting the same behavior, that means you have a problem with the IP, injectors, and/or engine. But we'll have to learn more about your WVO kit before making suggestions.

 

I prefer to drive vehicles with 3 pedals... but I do know that ~most tach problems on these engines turn out to be a faulty pulse sensor on the IP gear cover. Your E4OD transmission's computer receives rpm input from this same sensor and will not function correctly without this signal. Whether or not the symptoms of a bad sensor are like yours... I have absolutely no idea. Maybe someone with E4OD knowledge will chime in. The sensors are not cheap, around $70 online. Are you getting any check engine fault codes?

 

Here are some answers to questions and a few more symptoms I noticed when I picked it up and drove it home this AM.

Stopped by parts store and bought lift pump, a fuel filter, and an air filter (needed it anyway). Installed the air filter in the parking lot and noticed in the process that the throttle cable had slipped out of the little bracket it sits in on top of the engine. I fixed that and throttle response issue seems to be much better. Still have power problems though. On the way home I noticed three things. 1) Sometimes the car bucks when going up hills. This is worse in veggie mode, but present in both. 2) Problem appears to get worse when truck is warmed up. 3) Stalled out as I was cresting a hill. Took a look at the clear veggie fuel lines and there is more air in them than I remember. Was able to restart and limp home at 20 mph. 4) When I got close to home I tried shifting into 1st and flooring it up the hill. Can't get the tach above 2500 (it appears to be working for the moment). I'm increasingly convinced it's an air/fuel issue. Gonna let it cool down for just a few minutes and then go inspect for air leaks before installing the new lift pump or doing the ATF in the fuel filter. I bought a clear view inline fuel filter so I can pop that in to check for air leaks.

Genscripter - WVO system doesn't have a dedicated pump. I picked this vehicle specifically because of the mechanical vs. electrical pump for the veg. It's set up with three solenoids to have a diesel, veg, and purge mode. One solenoid is after the lift pump allowing me to redirect the fuel to a separate dedicated veg filter. From there it is T'd into the IP supply line (between the diesel filter and the IP). There are two other selector solenoids one on the return line causes the veg to loop back into the system when running on veg versus diesel returning to the diesel tank. The third solenoid gives me a purge mode so than at the end of a trip I can run it on diesel but instead of routing the diesel return back to the diesel tank, it backflushes the veg system to clear it of all veg oil.
I'm pretty sure the tank is aluminum and I know it has a copper heat exchanger on the inside. I'm pretty sure all the fittings are brass. I know the technology has gone to plastic tanks, but I've had this setup for a while and haven't had the time, money or energy to make a switch. As far as the IP is concerned, I was worried about that, but I have heard and read that usually you have starting and smoking problems before you have performance problems with the IP. Does this sound right? The truck starts great, every time!

Gonna go inspect for air. That's the simplest cheapest place to start! Will repost shortly.

 

Are you using the second diesel stock tank as the WVO tank? Then using the stock diesel selector valve to switch between veg and diesel? If yes, you need to STOP. Most of the stock lines are steel and the stock selector valve is not rated for biofuel. Also, the stock lift pump is not rated for WVO either.

I'm still confused on how you pump your oil into the IP. If you don't have a dedicated WVO e-pump, and you are not using the lift pump, then I must be missing something. I got lots of experience with veg kits, so I'm here to help. You shouldn't have any air in your fuel system, so work those problems out first. That is why you were surging and losing power. Depending on the brand of selector valves you have (some leak air if not properly bled) you could have air infiltration contaminating both types of fuel because the air infiltrating your WVO system is seeping thru the valve to affect the diesel side too.

 

i would stop using WVO and run straight diesel and see if it clears up. i bet it will.

 

Well, if he has a way to shut off the coolant heating to the WVO tank, then yes. But if it's hot all the time, it's typically a no-no to run 180*F Diesel from the WVO tank.

 

Along with all the other very good things to check, your IP can have power loss and still start right up and not smoke. Mine did. I bet your wvo has made the lift pump diaphragm angry and also it may have ruined your IP. the rubber line going to lift pump may be rotted from wvo.

 

I think he is confused with his WVO kit, because I'd be really surprised if he is using the stock lift pump to push the WVO. It is not recommended to use any of the stock fuel system (before the IP) for veg.

 

My understanding of what he said is that /after/ the stock filter head there are a few solenoids for switching between the stock system(dead-heading I guess when it's off... not sure what that'll do to the mech fuel pump) and a second electrically-pumped WVO system. So the join point is just before the IP.

 

When he wrote "WVO system doesn't have a dedicated pump," that kind of threw me.

You are right about deadheading this lift pump. not good.