clh Posted November 27, 2020 Report Posted November 27, 2020 +1 for yetti on this... It is very easy to temporarily swap 2&4 probes and verify there isn't something about the probes. Quote
carusoam Posted November 27, 2020 Report Posted November 27, 2020 Often... The technique of swapping the the high with the low injectors can result in a better GAMI spread... (Swapping the EGT probes can give some insight to see if there is a probe problem...) This depends on different airflow going to all the cylinders... or else the high and the low would just swap positions... The swapping experiment will tell you a bit more about the how the FIs are behaving... and something about the different air flows.. The other thing really cool about the swapping experiment... it can also determine if somebody accidentally swapped the injectors somewhere along the way... (some owners have found out they had Gamis after an unknowing mechanic wasn’t careful about their labels and cylinder positions...) Either way, the shape of the EGT curve of one of the FIs is not like the others... low, flat, early peak. (Regardless of numbers caused by sensor position) It would be good to get a new baseline of FF for each injector/line again... What is the cost of doing the baby food jar test? (In hours of work) It would be good to clean the FI that seems to give the errant looking line on the graph... use extra care to try and catch whatever may be causing the anomaly... some MSers have found pieces of a rubber fuel hose liner falling apart this way... Around here... there is descriptions of equipment and solvents used for cleaning fuel injectors... Hoppe’s #9 and ultra Sonics.... PP surmising only... not recommending any work to be done... Just trying to possibly answer, or give some insight to, the ‘what may be causing #4 to appear so lean’ question. Best regards, -a- Quote
Moonbat Posted November 27, 2020 Author Report Posted November 27, 2020 The “shape” of the EGT #4 curve is indeed different, an outlier, and troublesome. It is hard to believe that there is anything wrong with the injectors themselves. Two different sets, one brand spanking new, both show the same outlier in Cyl #4 regardless of the sizes of the jetting. Nevertheless, I will have another look. Swapping #2 and #4 sensors? Interesting, and what the heck, I’ll probably try that, but... as we all know, the absolute value of the EGTs is not terribly accurate. The fact that there is a peak to the temperatures is the important part, within reason. I expect the flattish shape of the curve to stay with #4 cylinder no matter what probe we put in there. Maybe worthy of a try, just in case though. Easy to do. What a surprise that will be if it follows the probe! As to the time required to do another baby jar test? Only a few hours at my amateur mechanic snail’s pace. Enjoyable few hours... Anecdote: Early on in the break-in process, we found cylinder #2 was taking over the leanest position from #4. I pulled the injector, and the eagle-eyed mechanic spotted the tiniest bit of thread goo across the injector port. Cleaned it out, and it was back to “normal” with cylinder #4 back it the leanest position once again. I can’t even recall how many times I have pulled these injectors - especially #4 - to look for this kind of resolution to the issue. Hope springs eternal. 1 Quote
carusoam Posted November 27, 2020 Report Posted November 27, 2020 An interesting variation on the food jar test... Done with and without the injectors on the ends... without the injectors, any differences will be fuel spider related... Then... with the injectors, any differences will be injector related... If you have a really accurate scale.... you can weigh the fuel caught in each of the jars... to increase the accuracy of the visual test... For home work in advance... identify where the rubber hose is in the fuel distribution system... see how old it is... it probably got replaced with the fuel system OH... (I am really missing this piece of knowledge) see Byron for this deep of a discussion on fuel distribution.... From reading around here... the rubber hose has been known to produce small parts that flake off and show up downstream... PP thoughts only, not a mechanic... Best regards, -a- Quote
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