Very recently, I began to experience what I thought was an ignition skip at low RPMs until I just now replaced the coil - having already replaced plugs, plug wires, complete distributor, PCV valve.

Engine misses/shudders when starting from dead stop then recovers... at cruise RPM 1500-2000 and not under load, engine misses intermittently... give throttle and engine recovers... when the "miss" occurs, the vibration can be felt thru the steering wheel, accelerator pedal, and shift lever. Otherwise engine will take all the fuel you can give and will come up through the gears without hesitation or surging... rock solid. But back off and just 'cruise' and you can feel the "skip" intermittently.

I was convinced it was ignition. Unless I have a bad new part, it isn't.
SO how about fuel delivery system? Will faulty fuel pressure sensor valve cause these characteristics - keeping in mind that engine is not running rough on accerlation OR deceleration nor surging. What about fuel pump? could that be the actor? To start the car for some time now, I must turn on ignition, let the rail charge, crank 2 or 3 times. Turn ignition off. Turn back on, re-charge the rail, and now it will start in two cranks.

Does anyone know what the PSI pressure reading at the rail should be and where the test port is located?

Appreciate any and all input. I've got 176,000 on this 1992 LX Coupe and I intend to solve this problem - with all the help I can get!
TIA.

 

Sounds likeyou might have a dirty / faulty EGR valve.
HJ

 

I was wondering if the EGR valve could be the bad actor... any opinion on the possibility of one of the injectors being partially blocked [I'm running a tankful of Techron through now] though under load, there is no stutter/hesitation under full throttle. Meanwhile, I'm not getting any check engine light....?

 

schrader valve or test port is usually located on the fuel rail. don't have the specs on me right now. I will get back to you.

 

In an attempt to confirm that the ERG valve was bad/not functioning and the cause of my "rough running" as described in my previous thread, I brought the engine up to operating temp, the "roughness" becoming detectable at idle [750RPM]... I pulled off the vacuum hose from the EGR valve and THERE WAS NO CHANGE IN ANYTHING! No check engine light.... and NO vacuum [to the touch] in the hose leading to the vacuum distribution box!
What gives?

Any suggestions?????????

 

OK,
You wont feel any vacuum on the EGR hose UNTIL the ECU wants to open the EGR valve. The ECU will send a signal to the electrically operated vacuum valve to open the vacuum port that suck open the EGR valve. When the valve opens it moves the arm on a potentiometer to give a feedback voltage to the ECU proportional to how much the EGR valve is open.

To test it :

You can simply pull the vacuum line off the EGR valve and hold your finger to the end of it, and rev the engine up and down. Crude but relatively effective to FEEL whether any vacuum is present in the hose.
Better test: hook up a vacuum gauge and rev the engine to see if there is any suction.

If you still don't see any activity, check the vacuum hoses to the EGR solenoid.


One of the most valuable tools to diagnose these kinds of problems is a simple hand vacuum pump / gauge. I have one called a "Might Vac".

Cheap but VERY effective.

Let us know what you find

HJ

 

If you use a pump, don't forget to apply 18 inches of vacuum. Observe the EGR diaphrahm and when vacuum is applied the diaphragm should move. If the Valve diaphragm doesn't move or doesn't hold the vacuum. Replace the EGR Valve. While your at it, make sure the rubber seal on your gas cap is not cracked or torn and your PCV Valve which is located on your valve cover is working properly. Pull the PCV Valve out and shake it. If it rattles, it works.

 

Ok, here's what I did/found:

With the engine hot and at idle [~750RPM], I applied 5" of vacuum to the EGR valve, having disconnected the vacuum line, and the engine changed noticeably [poorer to almost stalling]. From this I concluded that the valve itself was working mechanically. I then applied vacuum more gradually, and noticed that at as little as 1", the valve began to open and the engine sound changed.

With the engine hot, I measured 5 inches of vacuum with the EGR valve vacuum line connected to a gauge while increasing RPMs from idle to 4K. HOWEVER, the the gauge after registering 5", immediately fell to zero even while holding the RPMs at 4K. Should the vacuum have held at 5" peak until I returned the engine to idle??

I then "T"'d the gauge into the EGR valve vacuum line. I was only able to measure 1" of vacuum at 4K RPM and that also immediately fell off to zero after peaking at 1". Questions: shouldn't the vacuum have held while holding RPMs? any explanation for the diff of max vacuum with the gauge T'd in vs measured solo?

Even at idle, a subtle roughness is detectable. So on the chance that it could be a timing issue, I went looking for the timing marks on the timing belt cover. I couldnt find them! HELP here? But I advanced the distributor maybe 2 degrees then drove the car. I think I noticed a reduced incidence of stutter at cruise - i.e. 1500-1800RPM in 4th gear... however it was still present at low RPMs e.g. slowing to take a 90 degree turn, then accelerating. Stutter until some speed is built up.

Once again, full throttle on the straight from 35MPH and I'm at 6K RPM and blowing thru 70MPH rock solid in a *snap*!

Comments please.

 

OK,
You have checked the valve.
You know you have vacuum.
You know the valve opens
You know the valve shuts
Do you know if it is CLEAN ?
Periodically the valve seat will load up with exhaust deposits and not allow the valve to seat fully. I had to remove mine and clean it.
(Be sure to replace the EGR valve gasket when you do)
I actually put it into my sandblaster and thoroughly cleaned it ...
Just make sure you protect the rubber bellows part and the vacuum tube port.

As for the valve opening and shutting again - THAT IS WHAT IT IS SUPPOSED TO DO ...

The computer cycles the EGR valve open and shut continuously based on RPM and engine load.

If you still suspect the EGR circuit is causing you grief, then I would recommend replacing the EGR solenoid.