What is this?

[jaws5991]

At the rear/left hand side there is a black deal with the numbers 7841996 on it and it goes into the engine 6-8 inches, has a gear on the end of it and two wires connect to it. What is this, what is it's purpose, why does it have a clamp like the one that holds down a distributer, what happens if it is not turned to the proper direction? The motor runs but I have to spray it with WD-40 every time to get it started, it also has a large knock (timing?) when the power/gas pedal is pushed hard. So I have been searching the entire internet and all my engine books and can not find out what this does or what it is even called. Thanks.


1995 GMC P3500 6.5 NT Diesel.

[DmaxMaverick]

That's the engine speed sensor for PCM input (tach and/or tranny control, if it's MFI). Doesn't matter how it's "clocked", as long as it is tightened.

Your poor starting indicates any of the following:
Injector(s) kaput.
Timing way out (timing chain wear, pump out of range, if it's EFI)
Poor fuel quality.
Glow plugs/relay failed (likely, in any case).
Fuel supply air leak and/or leakdown (could also be a symptom of injectors beyond their usefulness).

The heavy knock is likely poor injector(s) health. If they have more than 100K on them, it's time for new/reman injectors. This would also cause very poor starting.

A bit more description and history of your vehicle would be helpful.

[jaws5991]

Thanks for the help. Is there a way to test the injectors? What is the best way to test the glow plugs? The truck has about 115000 miles on it. This motor was taken out because it sounded like it blew up, the dealership it was taken to before i bought it said the motor was blown. We put in another engine and it did the same thing right away. It turned out that the tourqe converter was real bad and was tearing the bolts right out of the crankshaft, which sounded exactly like a blown motor. We left the other motor in and had to replace the tranny and the T C and it ran great. I then did something really stupid and it was neccessary to put this motor back in. So this is just trying to get it back to running good. The injector pump is/was new when i bought the truck, less than a year ago, the glow plug relay is also new, less than 3 months old. It has the old timey gas pump on the motor and runs great at idle, after i start it with the WD-40. I will check the stuff you mentioned and again, I really appreciate the help.


1995 GMC P3500 6.5 NT Diesel
Automatic Trans

[DmaxMaverick]

With 115K on the engine, it isn't worth testing the injectors. The test will cost $50, or more, and a good set of injectors can be had for less than $300. Leaving in bad injectors can lead to serious engine damage, including cracked pistons and heads.

Test the GP's with a test lamp or VOM. Continuity is the test. If you don't know the history of the GP's, replace them with new. If they are AC9G plugs, replace them anyway. Use AC11G, AC60G, or aftermarket quick heat plugs (TDP advertisers (http://www.thedieselpage.com/vendors/main.htm) have them).

You have a mechanical fuel lift pump (old timey gas pump), and sounds like MFI (Mechanical Fuel Injection, DB2 IP), as well. Unless the parts have been mixed/matched. You may also have a 6.2L engine, which is OK, and a non-issue for all intents and purposes. Also, your injection timing is solely controlled by the rotation of the IP, so if timing is off, it needs to be corrected, and/or the timing set needs replacement. Much depends on the age/mileage of the replacement engine. A non-functional HPCA (Housing Pressure Cold Advance) will also cause hard starts.

Do whatever is required to get the engine to start well. The majority of the engine's overall health is indicative of starting quality.

[jaws5991]

The motor we took out, and now is back in, is/was a 6.5 and is the original motor to this vehicle, so the 115000 is correct. The one we replaced it with was a 6.2, which is the one that is really blown due to stupidity. The heads and crankshaft are still good if anyone in my area wants to buy them. I will get the glow plugs and injectors replaced. Thank you.




1995 GMC P3500 6.5 NT Diesel
Automatic Trans

[DmaxMaverick]

Was the fuel system (IP, lines) messed with, during/after the replacement? It is possible 2 injector lines are swapped at the pump. Verify your timing order coincides with cylinders. Even good tech's at dealerships get caught by this one, and I have too.

[jaws5991]

They were, I did mark and label everything first though. I will double check them all though. Thanks.