I have a 95 PSD and it started running rough, with no power. It was hard to start, so I checked the GPR and it was bad. I replaced it and now it fires up fine, but still runs rough with no power. After it fires up, it takes 2 seconds before the check engine light comes on and thats when it starts running rough. Would a bad glow plug (or multiple bad glow plugs) cause the PSD to run rough, with no power? Or should I be looking at a possible fuel problem?

 

Does it run very, very rough? If so, I think you are dropping one entire bank of cylinders. Starting ok, and then very shortly running roughly with the CEL coming on is an indicator of the IDM shutting down all the cylinders on one side of the engine.

The cause is a short at the valve cover gasket wiring connector. Do a search and you will find tons of info. Fairly easy to fix, and usually requires a new gasket and at least one injector wiring harness.

Start the engine, and check the exhaust manifolds to see which side isn't warm. This tells you which side to work on.

 

Yes, the driver side exhaust manifold is cold, and the passanger side exhaust manifold is hot. This must be the problem. Thank you! Where is the best place to buy an injector wire harness?

 

Ford stealership. Or International if one is available, as usually cheaper then Ford. I don't think anyone else carries it. Take the valve cover off before you buy one, as you will almost certainly need a new gasket also. About $50 for gasket and $30 for harness, depending on dealership.

Also be sure to check the connector that plugs into the outside of the gasket for damage. If this connector is melted it is harder to fix, and very, very pricey if you buy a whole new harness. I hear you can go to an International dealership and buy just the pins to fix this if needed. Do a search as the numbers are listed every so often.

 

MDB,

I am checking my wiring harness connector and wiring harness now for this symptom. Can you give me a pointer on exactly what a defective connector looks like and also what a defective harness looks like? or do I just need to do a search in the posts??
thanks,

 

OK, did a search of post and found what to look for.

Thanks anyway.

 

Yes you can buy the wire ends and a plug kit. Not all of the international dealers know this part number. I do not know it off the top of my head, but if you need the pt# call me 8-5 M-F @ 973-927-7300 ask for Rick or Harry and we will give you the part #'s

 

UPDATE: The truck is running great! It ended up being all the wire harnesses on the furthest right pin. Is this the glow plug pin? I changed the GPR, and it seems to get kind of hot when I was testing power on the terminals on the GPR. Is this normal? The passenger side wire harnesses are fine. It was just the driver's side wire harnesses. Maybe the old GPR was putting out too much heat to the drivers side glow plugs???

 

No, the GPR getting hot doesn't cause the problem because all it does is provide 12 volts to the glow plugs. But too frequent cycling of the GPR relay exacerbates the problem. The too frequent cycling is because the older PSD PCM programming cycles the glow plugs on EACH and EVERY time the engine is started for at least 1-1/2 minutes even in the summer. It stays on for up to 3 minutes or longer in the winter when the engine is cold. The WTS light goes out waaaayyyyy before the GPR is actually de-energized, because everyone would complain mightily if they had to wait for 1-1/2 to 3 minutes before they could attemp to start the engine.

The primary reason for this long on time is to slightly reduce engine emmissions on a cold start, but in my opinion, once the engine is running there is no reason for the glow plugs to be on anymore.

Anyway, the problem with the harness is multi-faceted. One, the glow plugs draw a lot of power, and wires and connector pins aren't very large. Any resistance anywhere in the glow plug circuit will result in heat being generated (remember ohm's law). Therefore, any slight corrosion or slightly poor connection at a valve cover gasket connector will result in heat, which progresses very rapidly, because heating the connector results in a looser connection and more resistance. As you can see, it is a vicious cycle.

Number two, the glow plug relay is energized much longer and much more often then actually needed. The longer a poor connection is powered, the hotter it will get and the more damage it will do. This not only is hard on the wiring and connectors, it also wears out the glow plugs sooner and it also wears out the GPR much more quickly then necessary.

By the way, a hot GPR indicates a GPR that is on its way out. The GPR is nothing more then a heavy duty relay, very similar to a starter solenoid. Any resistance at the relay's contacts = voltage drop = heat generation. Eventually the GPR will not make a good enough connection to provide enough voltage to the glow plugs and the truck will be hard to start.

Also, on the ealier PSDs the 2 outer pins (#1 and #5) in each valve cover gasket connector are each for a glow plug. Pins #2 and #4 are each for an injector and #3 is ground for these two injectors. What happens is that either pin #1 or #5 gets too hot and melts the surrounding plastic until the insulation for the adjacent injector is also melted. Once this happens the injector resistance gradually changes, and once it is out of specs the IDM senses there is a problem and shuts down a whole bank of injectors to protect itself.

It is good preventative maintenance to remove and clean all external valve cover gasket connectors occasionally. Clean them as best as you can, and especially look for any signs of corrosion and overheating. Then coat them liberally with electrical antioxidant grease, and reconnect them making sure they are properly seated. The grease will keep moisture out and prevent corrosion so that the connections stay as good as possible. You could also take the valve covers off and pack the connectors on the back side with the same grease, but this is a lot of work.

The best solution is to install a GPR bypass. Simply install a manual toggle switch or push button that lets you control when the GPR is powered. I installed a manual toggle switch that simply interrupts the PCM circuit and allows me to shut off the GPR before I crank the engine and leave it off after the first start of the day. Others have totally ignored the PCM circuit and just installed a push button that powers the GPR only when they push the button. This way they have total control of the time and frequency of glow plug use. It is recommended to de-energize the GPR before cranking the engine as this will signifcantly reduce the battery voltage draw, provide more voltage to crank the engine (higher cranking RPMs) and should help increase battery life.

 

Thanks MDB. A lot of good info. Question, I just replaced the GPR. Considering that it is getting hot, does that mean I have a bad new GPR? It is an Autozone MR99 and I am not sure if I have it hooked up the right way.

 

I would say that it is either undersized for the amp draw the glow plugs put on it, or it is a faulty relay. Heat in ANY relay is not a good thing, and either indicates resistance or overloading.

As for hooking it up incorrectly, this would be rather difficult as there are only four terminals. Two heavy duty terminals and two relay terminals. I am not familiar with the Autozone GPR, but I replaced mine with a relay from Grainger. I don't recall the part number, but it is rated at 100 amp and has silvered contacts (for better conductivity and less resistance). It only cost about $23 and should last much longer then the OEM type relays. It required a slight modification to install, but that is it. Do a search, as the number has been listed quite frequently.