1970s Rough idle

[shadetree39]

I have a rough idle issue on my '76 fuel injected Eldorado. The roughness is thru all rpm ranges. All engine vitals are good, compression,vacuum,plugs read good, etc. The Fuel injector manual suggests cleaning the injectors. I got two sets of seals one from eBay and the other from Rock Auto and they are quite different.
Previous owner had Heritage Cadillac in Lombard, Il install new injectors,seals in 2004. Car has been driven but 900 miles since. No leaks. Fuel pressure is 39 psi at key on and holds in the thirties at various vacuum draws from the regulator.
I don't want to remove the injectors and not be able to reassemble them leak free. Note pictures and their dimensions.
Note also the set that I got with the car #5720A740 marked FJ12 on package, look NOS. 
Which ones should be used? Is there a better source?
One set came with the filters. I got the old set of injectors and have been unable to remove the filter from them successfully .
Any suggestions.
The shop manual suggests cleaning the injector in a 1/4" of metal-prep for no longer than 30 min.   
Any help or suggestions would be most appreciated.
I would not rule out sending them out for cleaning if a reliable source is available.

[Jon S]

Before you go crazy, run a bottle of Chevron Techron and use the whole tank of gas.

[bcroe]

The first problem is to figure WHY the engine is running rough. 
An exhaust Wide Band OX sensor is a standard tool to see if EFI
mixture is good.  Could be it running rich which can be caused by
several things.  If your 76-79 EFI engine is running rich, check these.

The 500 engine must have the correct blue top, 49 lb/hour injectors. 
BLUE FJ12 or ACDELCO 2173452, also GM# 88864826

1. If you have 2 good ECUs try swapping them.  if it makes no
difference, they are not the problem. 

2. Assuming you have the right injectors, high fuel pressure or a
leaking injector could cause running rich.  Check with a fuel rail
pressure gauge, just turn on the key and pressure should come
up to around 39psi.  After the pumps shut off in a couple seconds,
the pressure should hold for some seconds.  If it instantly drops
to zero you may have a leaking injector, though a bad pump check
valve is possible.  Check that by pinching off the rubber hose from
the pumps after pressure builds up.  When you start the engine,
pressure may drop to more like 29psi, depending on manifold vacuum. 

3. Find the vacuum line that runs from the ECU to the Throttle Body.
Apply a vacuum at the TB end, there should be no serious leak.  If
there is, the engine will run rich. 

4. The 2 EFI temp sensors (2 wire) could be a problem if shorted to
0 ohms.  They should only effect cold enrichment.  Unplug them
after warmup to show, that is not a problem.  They should read in
the ballpark of 1000 ohms cold. 

5. There is one more thing to check. The heavy purple wire that goes
from the ign switch to activate the starter, also goes to the ECU
BLACK connector pin B. This needs to be pulled down to ground
by the starter load when not active, it affects mixture.  Sometimes
the under hood connector corrodes and leaves an open ckt to the
ECU. 

Unplug the ECU BLACK conn, at the harness pin B should
measure essentially zero ohms to ground.  You may also check
for zero ohms between harness BLACK conn pins B and E, the
latter goes to engine ground.  BLACK conn Pin B should light a
12V test light (returned to ground) when you blip the starter.
++++++++++++++
Aside from running rich, other things can cause rough running. 
Of course ignition must be good to all cylinders, with at least
minimum compression at all cylinders. 

6. The SPEED SENSORS located on the shaft of the HEI ignition
must be working properly.  I have seen seen on rebuilt HEIs, for
about half of them the rotating magnet assembly is turned around,
causing injection of the 2 injection banks to be backwards.  This will
cause rough idle, with less effect at speed.  I have attached a
drawing showing proper assembly at the lower left corner.  NOTE,
the rotor tip is much closer to the position of the top magnet, than
the bottom magnet.  If reversed, the pin can be driven out and the
magnets turned around. 

7. The OEM timing chain set on cars of this era needs to be replaced
with an all steel set. The original cam sprocket had plastic teeth
which can crack and fall off of old age, regardless of low miles. This
can clog the oil pickup and do more damage.  Ignoring the time
bomb threat, the BRoe rule of thumb is you can run with 2 degrees
of slack, 6 degrees means change it NOW. 

A loose chain has another effect on these MAP based EFI systems. 
The bad valve timing puts LESS air thru the engine, but the reduced
vacuum makes the MAP think it is taking MORE air, mixture goes
way rich.  A problem for MAP EFI, not for carb or MAF. 

I check timing set slack by muscling the crank around to put the
timing mark by the scale.  Or make your own mark.  Probably done
with plugs out.  Take the HEI cap off and note the rotor motion with
crank turned forward.  Now back up the crank and note HOW MANY
DEGREES the crank moves back before the rotor follows it. 
 
8. I have a special test ECU, which will check for a missing
SPEED SENSOR pulse.  Any time a speed sensor misses a beat,
it will flash a red LED.  It also allows varying fuel mixture over a
wide range. 

�BRUCE ROE
5719 EAST SKINNER ROAD,
STILLMAN VLY, IL 61084-9215    Phone 815 234-8039
K9MQG since 1958       solar powered since 2013