Brass Fitting on Injection Pump

[befland]

On some of the mechanical injection pumps (4911) there is a brass fitting on one injector ports (drivers side near the top). What is this fitting for? Is it just a spacer? The injector line for this port is also shorter by the length of the fitting.

[gmctd]

That is the piezo timing sensor - senses the mechanical expansion as injection pressure builds in the pipe - was a timing set that clipped onto it for injection timing reference

[befland]

Would it affect timing if I installed it on a pump that did not come with it?

I installed a 4911 on a 1983 6.2. I had to install a shorter injection line on one of the ports because the brass fitting was on the pump (injector line off a 1993 6.5). I recently replaced the 4911 with a 5209 pump because of hot start problems. The 5209 did not come with the brass fitting so I took it off the 4911 and screwed it on the 5209. After installing the 5209 pump my timing was off. Even though all my settings are correct...and advancing and retarding the pump...I cannot get it set correctly. I'm assuming it is the pump unless this fitting comes into play somewhere.

[DmaxMaverick]

The fitting won't make any difference. Not any you could tell, anyway. If you are having timing issues, look elsewhere. The fitting is designed to work with the short injector line (and vice versa).

Verify your firing order is correct. One pair of lines can be installed wrong easily, and a couple others can be installed wrong with some effort. Verify port #1 is in fact connected to the #1 cylinder injector, then confirm the firing order is correct for the rest of them. I know it sounds silly, but it happens, and more often than one would expect. All 6.2/6.5's have the same firing order and pump rotation. If it is anything other than the below drawing, something's amiss.......

[spiff]

About that piezo timing sensor; is there a way that the sensor could drive a tach? That seems to be a likely trigger. Does that sensor actually generate a voltage for each cycle of that individual port?

[gmctd]

Yes - that's exactly how it functions in the test set - just requires a preamp to up the signal to usable level, tho some a\m tachs do have a low-level preamp built-in.

Set your DVM to AC Volts, lowest range, place the test leads across the sensor to determine the effective voltage with engine idling - scope would be better for actual p-p level, tho you can do the calcs if ur DVM has true-RMS function.

If the DVM has frequency function, should see 1/2 idle speed displayed as frequency in hz - 4-stroke combustion cycle, cyl#1 fires every other crank rotation, right?

1-8-7-2-6-5-4-3

Surf the 'net to find a tach with suitable threshold - some offer external signal conditioners - just match your haves to their needs

Almost fergot - welcome to the 'Page, spiff.........

[joed]

In looking at the firing order in relation to the line postions on the pump:

Does the rotor in the pump actually rotate opposite of the engine? The drawing shows the back (towards firewall) side of the pump?

Not what I would have imagined.

Thanks. Joe.

[gmctd]

Correct - the camshaft is chain-driven off the crankshaft, so has cw rotation.

Inj Pump is gear-driven off the camshaft, so rotation is ccw - injector pipes are installed in cw rotation, viewed from the rear.

IH\Navstar used the Stanadyne IPs on the 6.9 and 7.3, with gear-drive - camshaft was then ccw rotation, making their DB2 IP cw rotation.

The ccw DB2-4911 is GM spec for the cw 7.3 DB2 - we got chains and gears, they got gears and gears - that's Chevy, for ya.

[befland]

All good info. Thanks Guys!

Bill