Need some help on this one. Its a 99 350 with rough running issues. 130,000 mi. Changed all fluids, checked uvc harnesses with meter and visually.

Ae shows some weird stuff. First it thinks the truck is an automatic when its a 6 speed. Owner says he's owned it since new and has had no electrical or warranty work perfomed. Buzz test shows P0263 and P0269 cyl 1 and 3 circuit control / balance fault. All 8 buzz the same. Contribution test shows P1668 PCM/IDM failure.

Trying to decide if I need to replace injectors 1 and 3. Is there a definite way to tell if these are bad. I don't like to throw parts at it without a diagnosis.

Also pulled a weird code P3494. Any ideas?

 

Have you run a contribution test? Checked rotational velocity readings? I'd do that then try pulling the passenger valve cover and unplugging either #1 or #3 and see what difference that makes in how the engine idles. Also see what the oil discharge looks like from those 2 injectors.

 

Chris has it covered as usual Only other thing, is your IDM modded?

 

Contribution test showed the P1668 code. Rotational velocity does not appear to be working properly. All cylinders reading 0.0. Not sure if I'm doing something wrong on this one. I'll pull the cover again tomorrow and look at the injectors while running.

As far as I know the truck is stock with no engine mods. He states he has owned it since new and has had nothing but normal service done. Still odd that it is throwing auto tranny codes and its a 6 speed.

Thanks for the suggestions so far.

 

Are you doing this test with a cold engine? It will read 0.0 untill the temp comes up. I have to put the high idle on for a few mins before the readings will start showing.

 

Thanks for the tip. Yes I was doing the rotational velocity on a cold engine. I'll try that again when warm. Any ideas what numbers i need to be seeing for a normal reading?

 

Under 3.0 is ok, but 0.0 is great. I am getting high numbers on #3 and #8. I have the gray CPS so I am thinking it is a false reading.

 

So higher numbers would indicate a bad injector? Or just more info needed on that cylinder? Even though its not my truck, dont really want to throw a couple injectors in and still have the issue. Looking for ways to diagnose IDM issues to.

 

Ok, did the rotational velocity test when engine was warm and still seeing 0's across the board. I am now unable to get the injector codes but continuously get P1668 with buzz test and KOEO. Truck runs but has obvious miss. Can find no problems with wiring by visual exam. Do not have access to break out box for recommended diagnosis. Any other ideas?

 

Poor mans breakout box: Partially unplug the passenger side injector harness plug from the valve cover gasket. "Rock" the plug to break contact with the front pins, which will kill #1 and #3 cylinders. "Rock" it the other way to kill #5 and #7. Sometimes you will find a loose or damaged plug/harness by doing this. They sell repair ends to splice on the harness.

Have you looked at the under valve cover harnesses? Sometimes they come loose part way and cause symptoms like this. How about checking the oil flow from the spouts on the injectors while you are there.