7.3 intermitent engine shake

Yerkie · Jun 1, 2015

Hi everybody I'm new to this forum so I hope this is in the right place!

Anyways I own a 2000 7.3 with 122,000 miles
Mods ts 6pos chip and air intake

The truck runs good at a cold start with a little shake to the engine not really even noticeable just to me but, once the truck starts getting warmer and to operating temp it has a shake while driving that feels like I'm hitting a little bump in the road every 2-3 seconds at random times. At a stop light it shakes pretty much the same but the rpms fluctuate about 50 back and forth. Also no codes

So far I have changed the oil and filter (was due) fuel filter, icp sensor and pigtail, cleaned the ebp tube and sensor because it was very clogged up. Just today I replaced the original black cps sensor. Nothing has made the slightest difference!

Yerkie · Jun 1, 2015

Also still when I unplug the new OEM icp sensor like the old one while the engine is at operating temp it clears the engine shake completely! What's going on?

Arisley · Jun 1, 2015

Do you have any way to monitor ICP? That's what you need.

Yerkie · Jun 1, 2015

I wish I did but, I took it to the guys I bought it from and he hooked it up to the computer/tablet looking thing and couldn't find anything running wrong. Of course it wasn't shaking at the worst point. He mentioned maybe the uvch harnesses or injector orings but, it still has a good bit of power and the injector orings I figure would be ok past 122,000 miles. I'm just stumped when the truck shakes/shudders it doesn't feel horrible I just know something isn't right with it

TyCorr · Jun 1, 2015

Take it somewhere that knows what they're doing.

SDS97_7.3 · Jun 1, 2015

TyCorr said:
Take it somewhere that knows what they're doing.

Says he's in Delaware. He could go to Airfish

golfer · Jun 1, 2015

Yerkie said:
Also still when I unplug the new OEM icp sensor like the old one while the engine is at operating temp it clears the engine shake completely! What's going on?

Unplugging the ICP sensor defaults the PCM to a static injector pulsewidth and ICP pressure (ICP pressure would 'read' 725psi on a scantool...but with the sensor unplugged, that's a bogus number).

the higher (725-ish) ICP pressure can make an injector (that may have a damaged/leaking plunger, OR a sticky poppet valve) flow a bit more fuel...making the miss seem less pronounced.

ie, if one injector were 'down' 5cc's of flow...if at idle the PCM was only requesting (the equivalent) of ~5cc's...that would be a dead injector (under those conditions)...

same injectors...(one weak-ish)...

now bump the ICP pressure (and/or increase the inj PW)...so that the PCM is requesting @ 10cc's...now you don't have a dead injector..you have a weak injector..which isn't going to be as noticeable as a DEAD injector. 7 flowing 10cc's..one flowing ??5cc?

that's my guess...

Yerkie · Jun 1, 2015

Airfish? I just found one close by but, haven't called yet. Also I unplugged the ts chip today to see if it was related and no difference with unplugged. Could it be the ipr valve or the little orings in it? mine isn't leaking but, it's definitely original and looks very pitted

co04cobra · Jun 1, 2015

golfer said:
Unplugging the ICP sensor defaults the PCM to a static injector pulsewidth and ICP pressure (ICP pressure would 'read' 725psi on a scantool...but with the sensor unplugged, that's a bogus number).

the higher (725-ish) ICP pressure can make an injector (that may have a damaged/leaking plunger, OR a sticky poppet valve) flow a bit more fuel...making the miss seem less pronounced.

ie, if one injector were 'down' 5cc's of flow...if at idle the PCM was only requesting (the equivalent) of ~5cc's...that would be a dead injector (under those conditions)...

same injectors...(one weak-ish)...

now bump the ICP pressure (and/or increase the inj PW)...so that the PCM is requesting @ 10cc's...now you don't have a dead injector..you have a weak injector..which isn't going to be as noticeable as a DEAD injector. 7 flowing 10cc's..one flowing ??5cc?

that's my guess...

Listen to what this man says...

You probably have weak injector that is being masked by ramping the icp up when sensor is unplugged.

You really need a shop that has a scanner that can run a few tests.

TyCorr · Jun 1, 2015

golfer said:
Unplugging the ICP sensor defaults the PCM to a static injector pulsewidth and ICP pressure (ICP pressure would 'read' 725psi on a scantool...but with the sensor unplugged, that's a bogus number).

the higher (725-ish) ICP pressure can make an injector (that may have a damaged/leaking plunger, OR a sticky poppet valve) flow a bit more fuel...making the miss seem less pronounced.

ie, if one injector were 'down' 5cc's of flow...if at idle the PCM was only requesting (the equivalent) of ~5cc's...that would be a dead injector (under those conditions)...

same injectors...(one weak-ish)...

now bump the ICP pressure (and/or increase the inj PW)...so that the PCM is requesting @ 10cc's...now you don't have a dead injector..you have a weak injector..which isn't going to be as noticeable as a DEAD injector. 7 flowing 10cc's..one flowing ??5cc?

that's my guess...

Following that logic, couldnt he leave the icp sensor plugged in, functioning, and unplug each injector and see which one doesnt make it stumble? Look at exhaust manifold runners with a IR heatgun?

Edit: mine was easy I knew it was either 5 or 7. Unplugged 7 first and bingo..

Yerkie · Jun 1, 2015

Thanks golfer what do you guys think about some injector cleaner into the fuel? To see if it would potentially unstick the darn thing/help it. Any brands better then others?

Yerkie · Jun 1, 2015

Yeah was going to take the valve covers off but, I don't get that much time off from work and it's my daily driver but, couldn't the "buzz test" determine the condition of all the injectors?

TyCorr · Jun 1, 2015

No. That will make the solenoids buzz.

Yerkie · Jun 2, 2015

Of course after changing out the black cps sensor for a grey one the idle is rougher. The weak injector makes sense cause now that I think about it when I unplug the icp sensor when it's idling at its worse it goes away but not completely. For the heck of it I want to try some injector cleaner cause I'm sure the things could use it.

What would you guys recommend? and I heard something about putting the cleaner directly in the fuel bowl? Any thoughts?

golfer · Jun 2, 2015

Yerkie said:
Of course after changing out the black cps sensor for a grey one the idle is rougher. The weak injector makes sense cause now that I think about it when I unplug the icp sensor when it's idling at its worse it goes away but not completely. For the heck of it I want to try some injector cleaner cause I'm sure the things could use it.

What would you guys recommend? and I heard something about putting the cleaner directly in the fuel bowl? Any thoughts?

each injector has two 'sides'...

the fuel side (plunger & barrel assembly, nozzle, needle, etc.)

and an OIL side...(solenoid/armature relationship, poppet valve, etc)

if the fuel side is damaged....adding chit to the fuel system isn't going to repair anything...

if the OIL side (poppet valve) is sticky..then possibly adding something to your ENGINE OIL could minimize/correct the stickiness..

I wouldn't waste a dollar on adding anything to the fuel system, but adding RevX or Archoil to the ENGINE OIL may help...

Yerkie · Jun 2, 2015

Gotchya. I'll try some of the revX stuff just to see if anything at all changes thanks!

SDS97_7.3 · Jun 2, 2015

Yerkie said:
Airfish? I just found one close by but, haven't called yet. Also I unplugged the ts chip today to see if it was related and no difference with unplugged. Could it be the ipr valve or the little orings in it? mine isn't leaking but, it's definitely original and looks very pitted

http://powerstrokearmy.com/forums/member.php?u=3497

Yerkie · Jun 3, 2015

I have pretty much decided after calling airfish and a couple other places local to me I'm gonna try to tackle it with a friend and do a couple other things while I get in there.

one thing I'm wondering is what is the best way to determine the injector that is sticking/weak? If possible for the time being I would like to just do the one valve cover with the bad injector/oring to take care of the main problem. Is there also a way to determine which one is bad before taking both covers off?

Yerkie · Jun 3, 2015

I have pretty much decided after calling airfish and a couple other places local to me I'm gonna try to tackle it with a friend and do a couple other things while I get in there.

one thing I'm wondering is what is the best way to determine the injector that is sticking/weak? If possible for the time being I would like to just do the one valve cover with the bad injector/oring to take care of the main problem. Is there also a way to determine which one is bad before taking both covers off?

Yerkie · Jun 15, 2015

7.3 bad uvch?

Hey everybody I have been trying to narrow down a intermittent shake at idle and while driving in my 2000 7.3 (122,000 miles.)

Everybody is pointing me towards a weak/bad injector but, I picked up a digital infrared thermometer and read each manifold pipe after running the truck a good 30 miles and they all read within about 10° of each other like cylinder 8-6-4-2 202° to 219° but the passenger bank 1,3,5,7 are at most 30° less then the the driver side bank. Also the shake gets worse as the truck gets to temp but at the same rate.