Cranks but don't start

Bigsexy

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So I was towing a truck home a few weeks ago and my truck decided to shut down on me when I let off the throttle. Ever since then it won't start. We had issues with the ecm not wantin to communicate with the systems so we replaced the ecm. Not it will crank all day long and actually produce some smoke when rail pressure ramps up. This whole time I haven't gotten any codes other then what the id's seen not communicating. It has fuel and rail pressure, and new filters. She's been burning a little oil lately but nothing to excessive. So I'm thinking of doing a compression check and I guess pull the injectors to see if somehow there's all bad. Anyone have any ideas of what it could be?
 

IHPowerstroke7.3

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If a couple cylinders were low on compression, it would still start. If all of them were a little low, it would still start. Seeing that it just stalled, problem is probably somewhere else. When you say "when rail pressure ramps up", they usually build rail pressure instantly. You could have a leak somewhere, check your oil level, see if it's over full. Could also be a bad frp sensor giving the truck a bad reading. Do you have rpm showing on the tach when it cranks? Could be a crank position/ cam sensor position issue. Need to hook up a good scanner and see what's what
 

Bigsexy

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We've been using ids scan tool on it, the vcv, pcv, and return pressure all looks normal. I'll have to check and see if the tach moving or if the vgt rod moves. If neither does what would cause it? The oil level is normal. I did just do an oil changes and fuel filters about 120 miles before all this happened. I wanna say I looked on the id's and seen crank and cam position reading
 

6.0 Tech

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Try unplugging the maf. This dont happen often, but i had the inlet to the low pressure turbo ff one at the shop the other day and when i wen to move it it wouldnt start. Everything loked good. Finally unplugged the maf an it started right up.
 

Bigsexy

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I'll try a few things you guy mentioned today and see what happens. I was stumped on it so I took it to my buddy's shop thinking they'd figure it out pretty quick but now there in the same boat I am on being stumped
 

Bigsexy

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I tried the maf sensor with no results, tomorrow I'll check compression but I'm wondering even if a hpfp will build 5500 could it still be bad to the point it won't start. It blows a little smoke when cranking also
 
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Might be the tuner. Long shot but had a buddy with h&s that wouldn't let his truck start and did some weird stuff..

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Powerstroke Man 6.4

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How much fuel in the tank? LPFP kicking on? and codes? voltage?

I know this sounds stupid but, spray alittle carb cleaner in the intake and see if it will kick, buddy of mine ran 6.4 died on the road out of nowhere it had 1/4 tank, towed it to the fuel station and filled her up full tank, RP was 5500 no codes, every thing was normal, no start.

Cracked the fuel bowl open and purged it closed it, used the the fuel pressure port to purge it the rest all and had a steady stream of fuel coming out still no start cranking, cranking and nothing, smoke out the exhaust etc etc.

I commanded 6500, it built it still no start decided to give the carb cleaner a shot, couple cranks and shots later she fired.
 
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Bigsexy

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It's has half a tank in it, the lpfp kicks on, still no codes, I have fuel in both bowls to. We have tried bringing it back to stock which should start once and run like cap but I've also tried switching from ******** to cales
 

Bigsexy

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So we checked compression and it's sitting at 280 on 2 and 320 on the other 2 on one side. Any other ideas?
 

Wizbangdoodle

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Early on with my truck, while it was still under warranty, I had the HPFP harness fail and it just stopped running. Would not fire again. Replaced the harness and all was good. I think there was a TSB on this.
 

IHPowerstroke7.3

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Compression readings are a little low, but you are in Colorado at 5000ft elevation. Relative compression showing good, just means the cylinders are equal in compression within reason. Only really good for showing a problem when a cylinder or two are down on a lot of compression compared to others. All it does is watch crankshaft speed during cranking, if one cylinder doesn't slow the crank speed down as much as the others, flags that cylinder. Either way, if you have 2 completely dead cylinders, it will still start.

Just because IDS shows you are building pressure, doesn't mean S***. I have had a couple no starts, frp reads and show fuel pressure around 5000 psi, still won't start. Worth it to swap in an FRP and the injector harness on that side, they go bad all the time.

If you are able to read pids, you can communicate with the PCM. Run a koeo test, injector electrical test and see if you have any codes. Bring up RPM, SYNC, VPWR, VREF pids. While cranking, make sure you have a rpm reading greater than 150 rpm. SYNC should read YES, that verifies crank and cam signals are reading and in time. Vpwr should be battery voltage, ideally greater than 11 volts. VREF should be steady at 5 volts. Have you tried clearing PCV and VCV learned values? Ive have also seen people change filters, not bleed the system, try to start the truck and get it full of air. They start eventually and can be fine for a while, but the pcm learns PCV and VCV values that are wrong that cause issues. Easy thing to try.

If all this shows good, going to need to do some pretty involved testing because you may have a leaking fuel injector.
 

Bigsexy

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So all that checked out find, if I'm building rail pressure would air leaking in an injector really be a problem?
 

IHPowerstroke7.3

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Its a possibility, I haven't personally had it happen to me. Before i would go through all that, I'd swap in a FRP sensor and the short harness on that side, especially if its never been changed before. Easier, less intrusive things first.

Few months back I put an injector in a 6.4 on the driver's side, cylinder #8 I believe. Ran mint after. Couple days later, came back, quit and wouldn't restart. Would show it building rail pressure, but wouldn't start. Talked to my friend that works at international, maxxforce's have same issue. Swapped in new sensor and short harness, fired right up. Have had others cause hard starts as well.
 

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