i have a 7.3 at work. crank but no start.

Pstroke96 · Nov 30, 2012

okay so a truck came in. 2000 fedex box truck grunman body if it matters. the truck died going down the road according to the driver. heres the rundown

the truck has a new fuel filter and pressure in the bowl.

all fuses are good

hpo resivoir is full

no smoke out the exhaust

power at the uvch plug. have not pulled the covers yet

un plugged icp still no start

cps is good

switched pcm with a known good unit

-now for the interesting.

no power at the gp relay on any terminal

no codes

will bang over on either, glow plugs disabled

where do i go from here? what would be the next logical step to check? i dont think it is the valve cover harnesses because it just died going down the road.

thanks for the help guys

Stroker#66 · Nov 30, 2012

Does it have icp pressure? A fast and easy way to check for a bad harness is to pop the oil fill cap off and stick your nose by it and see if it smells like burnt wires. I personally see a lot of hpop failures on FedEx/ups trucks I think mostly from lack of changing the oil

907DAVE · Nov 30, 2012

Check the engine harness fusible link, a shorted alternator can pop those and kill power the the GPR. However, the engine should still run...until the batterys go flat.

Any communication with the PCM? Do the CEL and WTS lights work normally? Buzz test results?

Pstroke96 · Nov 30, 2012

I can communicate with the PCM the wts and cel light function properly. We don't have the best software at the shop so I can't run a buzz test. I don't think all 8 would fail like that though

907DAVE · Nov 30, 2012

An IDM failure will kill all 8.

I'm guessing you dont have any codes either?

Pstroke96 · Nov 30, 2012

I am getting one code for air intake temp since the sensor is unplugged

907DAVE · Nov 30, 2012

PM sent.

Pstroke96 · Nov 30, 2012

Thanks for the info Dave I'm not working Tommorow but I will forward it to One Of the guys I work with I will report back soon as I know more. Thanks guys

ghohouston · Dec 2, 2012

check the oil? not trying to state the obvious, but a 7.3 will not start if the oil level is too low. ive had a truck that needed injector o rings towed into my shop before, put my scanner on it, couldnt figure out what was wrong with it, no codes or anything, checked the oil, and it was like 2 gallons low. check the oil, if its low, pull fuel filter, see if the fuel in the bowl happens to be black, if so, it will likely need injector o rings

Stroker#66 · Dec 2, 2012

ghohouston said:
check the oil? not trying to state the obvious, but a 7.3 will not start if the oil level is too low. ive had a truck that needed injector o rings towed into my shop before, put my scanner on it, couldnt figure out what was wrong with it, no codes or anything, checked the oil, and it was like 2 gallons low. check the oil, if its low, pull fuel filter, see if the fuel in the bowl happens to be black, if so, it will likely need injector o rings

He said the hpo resi was full so it's more than likely getting Lpo

ghohouston · Dec 2, 2012

Stroker#66 said:
He said the hpo resi was full so it's more than likely getting Lpo

you're probably right, but you never know, sometimes, we tend to over think the most obvious, simple things, and automatically assume it is something complicated

golfer · Dec 3, 2012

can you monitor ICP pressure while cranking?

the 2 most common causes of a no start on a 7.3L...

lack of cam signal to PCM (view rpm on scantool, disregard tach on dash)

under 500psi of ICP while cranking.

how many miles/hours on the engine/injectors?

Pstroke96 · Dec 3, 2012

Well we made some progress the fpr screen was packed full of some slimy crap. We cleaned the whole fuel bowl really good. It's not firing yet but we have smoke out the exhaust. I believe the injectors are original the hpop was replaced two years ago. There's 190 k on the ticker

golfer · Dec 3, 2012

i would clean more than the fuel bowl.

Pstroke96 · Dec 3, 2012

were going to run a couple of lines off the pump and into a bucket of clean fuel see if that gets it going

Pstroke96 · Dec 5, 2012

Turned out to be the hpop. I went abd gots set of gauges and put it right on the oil manifold. At a strong crank it was struggling to get over 300 psi with the ipr unplugged

golfer · Dec 5, 2012

Pstroke96 said:
Turned out to be the hpop. I went abd gots set of gauges and put it right on the oil manifold. At a strong crank it was struggling to get over 300 psi with the ipr unplugged

?

unplugging the IPR on a good pump would do that.

Pstroke96 · Dec 5, 2012

It was my understanding that unplugging the ipr would default it to peak pressure as a failure strategy. That is incorrect?

golfer · Dec 5, 2012

Pstroke96 said:
It was my understanding that unplugging the ipr would default it to peak pressure as a failure strategy. That is incorrect?

unplugging the IPR (which is a valve...not a sensor) would default the valve to an open position..ie, alllll the oil from the HPOP would be spilled right back through the front cover to the oil pan...resulting in a lack of pressure...usually around 250-275psi depending upon cranking rpm.

unplugging the ICP (which is a sensor)...will default the READING but have no affect on the actual (mechanical) HPOil pressure...

ie...unplugging the ICP sensor effectively blindfolds the PCM from knowing what the ACTUAL pressure is..however if you used a scantool to 'view' ICP pressure..you would get a reading for "pressure" but it would NOT be accurate, LOL..since you just unplugged the sensor.

But just for fun...if I go out and unplug the ICP sensor on my 7.3L..the truck would still start...and the scan tool would report 725psi at idle...and a mechanical gauge would show around 550psi.

Unplugging the IPR would cause a no start. and a mechanical gauge would read about 250-275psi.

a truck that has a HPOil LEAK...ie..it can't produce mechanical pressure...would still SHOW "725psi" with the ICP disconnected...but a mechanical gauge would still show the real pressure...which is unknown...but would probably be damn close to what you saw with the ICP sensor actually plugged in...doing its job.

so, I have no idea what you unplugged..

Pstroke96 · Dec 15, 2012

okay sorry it took me so long to get back to you i havnt been on the computer.

anyways i borrowed a good scan tool from a friend to see whats really going on and turns out our "good" cps was no good. so we got a new one and it started right up. thanks alot golfer. you saved me from spending a whole lot of not my money LOL