Quote:
Originally Posted by Bob Albrecht
Perhaps it is the lift pump. I am going to have a look at it.
Does anyone think it could be a bad injector?
When I replaced the primary filter there there were no bubbles. I probably should bleed the injector lines after replacing the filters, but the last time I did that it made no difference. The system is supposed to be self-priming.
There is an overflow return line. How would blocking it help?
Yes, it does have a goofy design for the fuel heater. There is a piece of plastic that can crack over time. The seals can also go bad, which is what happed to me. I replaced it not too long ago, so I checked that. If it is bad it leaks slowly and can drain the IP, especially if it has any weak seals.
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Blocking the output temporarily tests to make sure the relief valve has not gotten so weak the low internal base injection pump fuel pressure is causing idle issues.
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f this does not correct the idle and the return line you are blocking was flowing fuel prior to the closing off. Then an assumption can be made the fuel pressure is in a workable range or not a problem. Actually this test does have a few issues but in general can indicate things. The ideal test is more complex.
Anyways the easier test only really clears the relief valve of fault. It does not clear your lift pump of any suspicion totally in your case as well. How the engine acts with the line closed does indicate things though but you have to think about the reaction you are seeing.
Since your model does have that fuel heater. Submerging the fuel return line in a container and watching for any air being processed with the fuel is the best test for air in your system I can think of. There is no chance of error in interpretation. That heater is well past the primary filter so there is no other way to see if air is getting into it. Unless the return line is pretty clear.
I cannot dispute your thoughts on a dirty injector. Reading the milli volts from each glow plug at the harness when the idle is very rough would locate the injector if questionable.
The milli volt reading would be very low on that glow plug. The ground for the meter must be to the engine itself. Or very high if the injector was staying totally open I suspect.
A guide to the suitability of your existing glow plugs being used for testing is the range of readings obtained from all the other glow plugs. Idealy they should be a newer matched production batch.
The real world does not always allow this though. So you extrapolate what you have. This is a good way to check injectors for a dud. Since it is a dynamic test. It will catch an intermittent injector where a static or straight test probably would not.
I have to use tests as I am not smart enough to determine what the problem is by guesswork. When combined with buying expensive parts that are not needed or shot gunning problems. I resort to testing instead as I find it less frustrating.
Not being a working mechanic is a big disadvantage. I have no intuitive feel developed over the years that they have developed. So I compensate for it the best I can when required. It seems to work out but again I have endless years troubleshooting things other than mechanical under my belt.
Given that you have several choices at this time. When the idle is rough I would want to examine those milli volts readings. As it is so easy to do and can give useful information or eliminate things.
That is where you save money and time. Only takes a five dollar meter to do it. You may even have a meter now. If you want to get technical two readings would be vastly superior. One reading with the normal idle and another after the roughness has been established for a minute. The meter ground must be to the engine again remember. If the readings remain the same rough or smooth then is the time to look elsewhere in my opinion.