My 92 v8 5.0 is having trouble before it warms up with the idle "chugging" Everything points to the fuel injectors...I read lots of real good info on these tech boards, am wondering how much of a job this really is? And as many times as I tried to resolve it prior to driving it (rev it, rev it, rev it and then turn it off and restart) it still "chugs" and idles EXTREMELY rough. How much damage am I doing driving it like this? In the afternoon when temps warm up, it's the beast it should be....

 

The best way to determine of the injectors are a problem is to diagnose the system. The FIRST thing to do with any Delco Multec injector system is to disconnect the injector electrical connectors and measure the DC resistance of each injector with a reliable ohmmeter. Expect to measure a resistance between 12-16Ω for each injector solenoid coil. Lower resistance indicates a solenoid breaking down (insulation failure) and higher resistance can indicate corrosion in the injector coil body. If the injector resistances are tested with the engine cold, start and warm the engine to full operating temperature and test the injector resistances again. If the measurements fall below the specification a weak injector coil can be the cause.

If the injector resistances are within acceptable specifications, measure the standing fuel pressure with the engine idling. Measure pressure with the vacuum supply connected to the regulator, and then measure pressure again with the vacuum supply removed. If the pressure is about 35-39 PSIG with the regulator connected to vacuum and 40-47 PSIG with the regulator removed from vacuum we can presume the fuel pump and regulator are performing properly.

If the pressures test correctly it would be helpful to perform a power balance test. Injector relative delivery flow (power balance) tests can be done fairly easily with only a little diagnostic equipment and some time. If you are certain the ignition system is functioning and you have good compression on all holes, you can perform an effective power balance test to locate the offending cylinder(s).

To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling. Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. A diagnostic tachometer is much better for this than relying upon the instrument panel tachometer. Replace the electrical connector and go on to the next injector. The ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place. The drop in idle RPM as each injector is disconnected should be relatively equal through the firing order.

Compare the RPM drop at each cylinder. Remember to replace the IAC connector after the results are recorded. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate, may be sticking or leaking, or may have a poor spray pattern.

NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.

 

As for damaging anything, that depends upon the cause. If the misfire is due to leaking injectors the result can be that raw fuel is entering the crankcase, diluting the oil, and potentially reducing the lubrication effectiveness. If this is the case there might be a fuel aroma in the engine oil and the oil level may be higher than intended. This would be a concern, causing a fairly immediate need to resolve the problem.

If the misfire is due to stuck, failed, or clogged injectors, the lack of fuel should not cause any damage other than the possibility that eventual oil accumulation in a cylinder might foul a spark plug. You could drive it indefinitely that way.

The real answer to the question is determining the cause. Estimated of potential damage can then be considered.

 

Well, being TBI, a lot of what applies to a port-injected motor doesn't translate well... good suggestions as always, just, not applicable.

In the case of TBI, it takes nearly as long to open and close the hood, as it does to "rebuild" the injectors. I'd suggest starting there. TBI injectors hardly ever "go bad" in any irrevocable way; they just get dirty and their sealing parts develop leaks.

Go to yerbasic local parts store and get a paper-&-rubber kit for your TB, and pick up a gallon of lacquer thinner from yer local hardware store. Tear down the TB completely and soak all the metal parts in thinner overnight. Put it back together with a bit of spray silicone lube on the gaskets & O-rings.

Whether that will fix "The Problem" or not is open to debate; however your car will run SO MUCH BETTER, you'll kick yourself you didn't do it sooner and more often, as eeeeeeeezy and cheeeeeep as it is.

Likely cause of poor running when cold is the coolant temp sensor. Those are even more cheeeeeeeeeep and eeeeeeeeeeezy to replace. Might want to just pick one of those up at the same time and do it too.

 

MR. B - Good catch! I didn't read closely enough to see that it was a TBI system.

'Scuse me whilst I wipe this egg off my face...