Trying to recycle a CNG only engine, it would not idle nicely, if put it in gear it drove ok but it had strong shudder & no power on hills @45mph and you could push through that with more throttle then it would choke/shudder again around 55mph and you could push through that. At those speeds if you didn't give it gas it would shudder and shake the 'driveline' (only way I can think to describe it) enough that it you could feel it in the steering wheel, the whole dash would shake. I found loose bolts all around this E350 from me driving it 500 miles with the shudder I suspect! The van was low mileage/like new, so I converted the whole system to gas: new fuel tank, lines, fuel rail, injectors, spark plugs, PCM, etc. Upon first driving the system was running fantastic with just a hint of pre-ignition (sounded a bit raspy) and would accelerate up to 50-60mph without a hint of shuddering but if you accelerate quick around 30mph or on a long hill it would bog down and run really rough similar to when it was running on CNG! Push through to higher speeds smooths it out but really doesn't sound good under load in the mountains (45mph in 2nd gear is about all it can do smoothly). The shudder may be gone from tightening down the 2? transmission mount bolts that were some of the loose fasteners I found going through this process. Any ideas about the viability of this engine? Are there some internal conditions that would exhibit this way (regardless of the fuel system/detonation)? As it sits it could be a nice delivery van running a flat route, engine only has 30k on it and was driven only around a flat college campus @ 20mph. Thanks for any ideas!

 

It sound similar to those who have had short cycling of the COP's ( coil on plugs). Don't know if the CNG systems were using the same ignition or not, but presume they did. The only real way see this is use a scanner that is capable of mode 6. That shows ignition firings for each cylinder and when your described condition happens the ignition counts drop, there by pointing to the cylinder or multiple cylinders that it happens on.

Have you scanned for codes? Have you checked for vacuum leaks? This van was it governed so only go so fast?

 

thanks for the info re: scanner type, would that rule out the auto parts store for scan/diagnosing?

this is a problem child since I have not connected all sensors yet, some gasoline sensors are not present in a CNG only system, I am looking for a clean/correct year wiring harness to get everything talking at which point I am hoping to get a thorough scan.

I have not checked for vacuum leaks, any other symptoms that would indicate vacuum issues?

how could I tell if a speed limiting system was in place?

tnx again!

 

Yeah I'm guessing that you're gonna have get all the sensors and gas wiring harness and ECM in place before you make much head way on this. Probably the governed system was programed into the ECM, might be able to get your CNG ECM re-programed for typical gas platform?

 

If you have a mass air flow sensor, which you should, make sure all the intake boots and connections are tight, and clean the MAF with starting fluid, MAF cleaner, ect. What you are explaining is exactly what a dirty MAF will cause.

 

Just picked up a high mileage 5.4 with similar problems, mechanic changed out the plugs and coils and runs very well now. The rubber boots on the coil packs deteriorate letting the spark go to the engine block instead of the spark plugs, as the load on the engine increases the resistance on the plugs increase making the problem worse. You can purchase the rubber boots separately for around twenty bucks.

That said, I don't know if they made programming changes to run on CNG or any other modifications that would need to be changed.

 

thanks y'all.

I do have the gas ECM in there (wouldn't start with the original CNG one) and some of the wiring but not all. I will clean the MAF (it looked clean, like everything on this low mileage van, the oil looked like honey! but maybe that is because CNG fuel is cleaner)

SOOOoooo, I expect another 20 hrs of tinkering to get to where I could try a scan, anything SCREAMING internal damage to engine that would make it not worth going further?

thanks tons.

 

I would try some new coils or like I said just replace the rubber boots. I bought a new set on ebay for $39. Every used Ford I've bought I've put new plugs and coils in. Every truck ran rough with a load on them. People won't spend the money to have them serviced (expensive ). With only 30k miles it should have a long life with regular maintenance.

It could be something else but would not cost much to try the coils or boots.

 

I forgot to list COPs, I got Motorcraft OEM from Amazon seller (came with a certificate of authenticity, scam?) so I think those are good. they look just like the ones from the dealer without the Ford packaging...