nunan Posted March 23, 2012 Share Posted March 23, 2012 Doing a side job with a friend of mine. it's a 94 f350 that will not start. Previous owner had it break down with no restart, and then he abandoned the truck for a good 4-5 years. Fastforward to a few weeks ago, the current owner bought it off him thinking he could get my friends dad to fix it (works mainly on old mechanical diesels, restores construction equipment/trucks from the 30s to late 80s). Him, his son (another diesel mechanic for a standby generator company) and myself are trying to figure a few things out. They had initially repaired the wiring harness going to the engine from the bulkhead due to severe rat damage (couldnt get the engine to turn over with key). So they said they fixed all the circuits in that harness (was done with wire nuts..not a huge fan of that) So i checked the basics first. oil level was good, we eliminated the fuel tanks and ran a aux tank full of fresh clean diesel, changed the filter. tried crankin and was getting nothing. My friend had the valve covers pulled before I got there, and it seemed like we were getting no oil up to the heads. So i'm thinkin base oil problem. We eventually pulled the oil cooler to see if we were getting oil from the LPP, and we're not. So thats why the previous owner abandoned it probably. But before they told the customer that it needed an oil pump, they wanted to verify there was nothing else wrong with it. I'm not a big fan of turning over an engine that knowingly has a bad oil pump, especially considering how long its been sitting out of service. But they both insisted we check, so once i made sure they knew it wasnt my idea, i continued helping. I wanted to check for codes, but my scan tool wasn't hooking up. so after i couldnt get it to communicate, i decided to manually check for a few things. Found out I'm not gettign a 5v reference to anything. I found that the PCM and IDM relays were not getting triggered on, due to a wiring fault somewhere in the coil sides of those relays. So i hot wired the relays from a fused power source, and turned it over. CMP was not getting anything back, but it still wasnt getting a 5 volt reference. I followed the PC/ED as much as I could, and kept getting told to replace the PCM. I cant find the PCM anywhere and they do not remanufacture them anymore. So i need help on trying to locate a new PCM for this beast, or atleast pricing. Also, could anything else be causing my 5 volt reference to not be showing up? One other question. For the PCM to tell the IDM to fire the injectors, does it need to see base oil pressure? any help would be great, thank you. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted March 23, 2012 Share Posted March 23, 2012 Also, could anything else be causing my 5 volt reference to not be showing up? One other question. For the PCM to tell the IDM to fire the injectors, does it need to see base oil pressure? any help would be great, thank you. Any shorted 3 wire sensor will cause VREF to go away. I've seen it several times, like with the ICP. It doesn't need to see base oil but it DOES need to see .8v min ICP to enable the injectors. If you unplug the ICP it will turn on the injectors regardless of OP/ICP pressure. Backprobe the ICP and watch voltage, it should be .18-.24 KOEO and build 1.5v cranking. Is the HP reservoir full? If you take the oil filter off will it puke oil there? If you fill the reservoir through the plug on top it should build ICP for a minute regardless of LPOP. (ugh) There's a "de-aeration" valve in the back of the timing cover on early trucks that has a bad habit of falling out, causing zero LPOP and a no start because of no HPOP. TC removal is out with the engine and off with the pan first. Also, early trucks had another nasty habit of losing the oil filter relief valve, causing the engine to get unfiltered oil 100% of the time. It should be visible under the filter, staked in place to the filter header, about the size of a dime. If it's missing you may be wasting your time as the whole engine will be full of debris and the oil cooler can get clogged because it now acts as the filter. If it's a virgin '94 it does not talk through the 16 pin under the right side of the dash, it will only talk through the EEC4 connector by the left hood hinge. Most of them were flashed/new PCM to update this and you need to tell the scan tool it's a '96. I still see virgins occasionally. Good Luck! Quote Link to comment Share on other sites More sharing options...
lmorris Posted March 23, 2012 Share Posted March 23, 2012 I usually start by unplugging everything on the motor and the accelerator pedal. Then check for vref. Plug in each sensor one at a time to see which one is the cause. Don't forget this engine only needs the CMP plugged in to run. Also watch the tach when cranking, it can be a quick check for a bad CMP once you get the vref figured out. Pay very close attention to the engine harness where it goes down in front of the turbo. They like to go bad in there. Check all body grounds as well. Seen a loose ground cause similar issues. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted March 23, 2012 Share Posted March 23, 2012 Edit: We eventually pulled the oil cooler to see if we were getting oil from the LPP, and we're not. So thats why the previous owner abandoned it probably.Is the cooler still off? If it isn't puking oil from the front-cover-to-cooler flange, it's time to find out why. I'd pull the glow plugs so the engine will spin freer and overfill the crankcase in case the pickup tube is cracked (somewhat common) causing no LPOP. (another edit- use only a 1/4" ratchet, NO AIR TOOLS to pull the GP. If one starts to get "tighter" as it comes out, put it back in and leave it alone. 7.3s like to balloon the GP tips and break them off on removal, which is bad news. They work just fine on 7 GP.) Spin it and see what happens, maybe the pump lost its prime from sitting, or the tube cracked/aeration valve fell out or something. If the GP are out, pan is overfull and still nothing comes out of the TC port (to cooler) try gently blowing some air into this same port. If the d-a valve is missing, air will blow directly into the crankcase via the missing valve hole. You could also apply some gentle vacuum here and see if this port is open, like stuffing a piece of heater hose into the port in the TC and sucking/blowing on it with your mouth. If the DA valve is missing there will be no restriction and you'll be able to breathe through the heater hose. From the Gen 2 coffee table book, note pic is of the backside and pic is rotated 90 degrees: ESN is just behind the oil filter, very easy to read, if you want to know if your engine falls between the SN limits for the DA valve. Not my picture, valve missing: Quote Link to comment Share on other sites More sharing options...
nunan Posted March 23, 2012 Author Share Posted March 23, 2012 bruce you're the man. That should help me out immensely! Thanks Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted March 24, 2012 Share Posted March 24, 2012 I followed the PC/ED as much as I could, and kept getting told to replace the PCM. I cant find the PCM anywhere and they do not remanufacture them anymore. So i need help on trying to locate a new PCM for this beast, or atleast pricing. Also, could anything else be causing my 5 volt reference to not be showing up? If you get oil and are on your way to a PCM, install a breakout box and check your powers/grounds against the colored diag sheet. I have a known good used 7.3 PCM but I think it's Gen 2. www.car-part.com has plenty of them, make sure you get it for a '96. Good Luck! Quote Link to comment Share on other sites More sharing options...
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