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Jonathan Pell
Jonathan Pell, ASE Certified Technician
Category: Car
Satisfied Customers: 137
Experience:  ASE certifications, Many years in the field, and graduated from Wyotech with degree in Auto, diesel
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1994 b4000: misfires..Fuel pressure is right in the middle

Resolved Question:

1994 b4000 it has multiple random misfires. New plugs and wires. Fuel pressure is right in the middle of the pressure ranges. Ignition control module and coil tests good. #4 cylinder does not seem to ever misfire, but the other five cylinders hit and miss randomly. More prononuced at low rpm's. Autolite plugs and wires were used. It does have high mileage, but still has good power. (when all cylinders fire right) Noid light on injectors that would heavily misfire was consistent, no misses found from injector. So cylinder should be getting fuel, its just not getting fired on the ignition side. I'm at a lose. I no longer have access to obd1 scan tools. The check engine light is on but I don't know the codes. sorry. If the injectors are firing right, the engine starts and runs somewhat, that tells me the crank and cam sensors are ok. Any ideas? Please help me.
Submitted: 5 years ago.
Category: Car
Expert:  Jonathan Pell replied 5 years ago.
Hi my name is Jonathan, The only way I have found to retrieve the codes are from a dealer or any other shop that performs diagnostic work. They can usually pull codes for cheap. It sounds like if you have tested all of those components and tested good then your injectors have internal damage, just because the noid light test is normal means that the injectors could be dirty and clogged up. My sugesstion is to replace the injectors instead of cleaning them. You can also switch the injectors from cylinder #4 to another one since that one is not misfiring and see if anything changes.
Customer: replied 5 years ago.
its the spark out of the coil that is inconsistent. why is the fire out of the coil inconsistent? other than the igniton control module what controls the cylinder firing?
Expert:  Jonathan Pell replied 5 years ago.

Have you checked the crankshaft position sensor, sometimes they can cause a false signal or intermitten signal to the ignition control module. It sounds like this is the culprit. Here is a diagram of the entire system and explains how exactly it works.graphic

Customer: replied 5 years ago.
If the ignition control module converts the crankshaft position sensor input into a camshaft position signal, like the diagram states. Why isn't the pulse on the injectors inconsistent? Shouldn't I have problems with stalling? I don't. It doesn't matter if this thing is hot or cold. Unhook the battery, It just doesn't care. It runs the same. And yes I am pulling my hair out.
Expert:  Jonathan Pell replied 5 years ago.

What it means by changing it into a camshaft signal is basically just stating that it switches the signal from ac voltage to a dc voltage like the camshaft sensor. It does not combine the signals. I would start with the crankshaft position sensor and have the injectors cleaned or replaced. If all of the components tested good from earlier than the only other possibilities are the crankshaft sensor and the injectors clogged up or leaking internally. I can send you test procedures for the crankshaft sensor if you would like.

 

The pulse to the injectors is fine because it gets its information from the camshaft position sensor. The information for the spark comes from the crankshaft sensor. I feel very confident that the crankshaft position sensor is problem.

Jonathan Pell, ASE Certified Technician
Category: Car
Satisfied Customers: 137
Experience: ASE certifications, Many years in the field, and graduated from Wyotech with degree in Auto, diesel
Jonathan Pell and other Car Specialists are ready to help you
Customer: replied 5 years ago.

Ok Jonathan I'm going to accept your answer becase it is probably right. But apparently I had a dumb blonde moment. My bad. A spark plug wire burnt pretty much in two pieces, and going straight to a very good ground. Apparently taking most of the coil's output.The one wire that appeared to be the only firing correctly. Replaced the plug wire and all is smooth running. Like I said it was my screw up. FYI a Snap-on Advantage does not show ckp sensor output on this model. Thank you for your time, and effort to help me. If or when I need help like this again, I'll be back for help. Thanks again.

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