Cat engine 3126
Luke

Flushing, NY

#189 Dec 10, 2008
Hi,
I have a 2001 GMC with a 3126E with 130K and it seems to be low on power, how do I check to see if it is the HEUI pump? It has its original HEUI pump, IAC valve and sensors. On occasion it will start and run rough but will smooth out as it is driven, it uses little to no oil. Can a bad HEUI pump cause a low power on the highway issue? It can barely keep up on flat roads and will lose speed on the slightest grades while other trucks drive right by and the truck is almost never loaded heavily usually around 32-34K (tandem axle truck with GVW of 52K). I use synthetic oil and cat fuel filters.

Thanks for the help,
Luke
Luke

Flushing, NY

#190 Dec 10, 2008
sorry also forgot to mention in my post above, it is a 250 HP 800 lb/ft torque flashed to 275 HP 860 lb/ft. No noticable extra fuel consumption, truck seems to idle fine.

Since: Dec 08

Edison, NJ

#191 Dec 12, 2008
I have 1999 fl70 with 3126 changed #5 injector wont start only with either,runs for about aminute than shuts down.pulled out injector to check o ring and found it to be ok put it back together and still the samething help!
BKBREA

Bell, CA

#192 Dec 17, 2008
Sorry to hear so many issues with the 3126. I have a 1997 3116e (the predecessor to the 3126) that has never given me any real problems other than not enough power. But with 95k miles and no error codes, knock on wood.
Dawson

United States

#193 Dec 28, 2008
I need torque specs for my CAT 3126B engine in my Freightliner. Any ideas?
Jerry

Henderson, NV

#194 Jan 2, 2009
These people are absolutely right about servicing the 3126! When I bought my 2000 FL 60 to hotshot with, I didn't no how many miles were on the last service. When I put 10,000 miles on it after I bought it, it began to miss at idle and would cut out going down the road. I did a complete a complete service including oil and fuel filters and the truck is better than ever!
FYI
Jerry
LimitedEdt FarmsFreight

Eddyville, KY

#195 Jan 3, 2009
eric wrote:
i have a 3126 cat in a forestry truck.problem is i am losing oil, cannot see any visual leaks and no smoke out exhaust. any suggestions?....ive gone thru 6gal of oil in 1 1/2 weeks
My 2001 Freightliner FL70 was using oil just like yours. Turned out that the oil pan so loose it almost fell off. I would check that first.

Since: Jul 08

Location hidden

#196 Jan 4, 2009
DJW82 wrote:
I have 1999 fl70 with 3126 changed #5 injector wont start only with either,runs for about aminute than shuts down.pulled out injector to check o ring and found it to be ok put it back together and still the samething help!
I believe your engine is a mechanical 3126.
if so, i higly suspect the problem is the injector seat.
Each and everytime you remove an injector the bottom seat MUST be machined before you install the same or a new injector!!!.
if not the injector will not seal to the seat and will cause combustion air to leak into the fuel gallery (passage). this will cause the engine to run rough, bad starting, intermittent shutdown, low power, and eventually broken injectors for sure. the only way to make sure all injector are sealing properly is to install a sightglass between the fuel returnline and the tank. if theres no air bubbles within the return fuel flow the problem lies elsewhere. there have been cases where the injector was installed without the proper installation tool and this caused the injectors to become loose after a short period of time creating air in fuel. you need to contact a cat dealer for the tooling. hope this helps
guatruck

Mixco, Guatemala

#197 Jan 10, 2009
Hello, I own a freightliner truck with 3126 engine model. The engine do not start, There is not pulse from the ECM to the Pressure valve. I start the engine directly, put a 12v line to the pressure valve and the truck start, but it has a really bad noise, maybe to much pressure.

But now, I donīt know what to check, Why is not pulse from the ecm to the pressure valve??
Should I check the timming sensors? or is the ECM bad?

thank you for your help

Since: Jul 08

Location hidden

#198 Jan 11, 2009
guatruck wrote:
Hello, I own a freightliner truck with 3126 engine model. The engine do not start, There is not pulse from the ECM to the Pressure valve. I start the engine directly, put a 12v line to the pressure valve and the truck start, but it has a really bad noise, maybe to much pressure.
But now, I donīt know what to check, Why is not pulse from the ecm to the pressure valve??
Should I check the timming sensors? or is the ECM bad?
thank you for your help
sounds like your engine has a major active faulcode that prevents the engine from starting, thus disabling the injection. the bad running sound is most likely a combination of the component that has failed and extremely high injection actuation pressure. once you give the IAPC-valve full 12 volts directly from the battery the valve commads the HEUI pump to generate the maximum attainable pressure since the valve is operated by specific current from the ecm. contact your nearest dealer for fault code readout and diagnostics.
i recon you may have a failed injector or the HEUI pump is worn from its normal operating range.
guatruck

Guatemala City, Guatemala

#199 Jan 12, 2009
Hey, today we check the truck and doesnīt have any faultcode.

So they remove the ecm and seems to be ok, to. I do not understand why do not start the engine.

Does anyone have the wiring diagram for engine 3126?

The IAPC-valve recive pulse from?? ecm? please help,

Or do you think is the ECM?
gasman

United States

#200 Jan 13, 2009
I own a fuel station and I have a customer who complained about the same issues I'm seeing on here. 3126 is hard starting won't run right. Comes back two weeks later and says that there was gas in the diesel tank and had to have two fuel pumps removed all sorts of orings and other work. total shop time added up to 49.5 hours at a cat dealer. This sounds like he may have been having same problems as everyone else and is trying to have me pay for the repairs.
guatruck

Guatemala City, Guatemala

#201 Jan 13, 2009
help?

Does anyone have the ecm wiring diagram for the 3126?

There is not codes, Later I got flash codes, and only flash #49.

NOt more, but not pulse from ecm to IAP ...=(

thank you
Todd Kokorudz

Canada

#202 Jan 15, 2009
Stevie wrote:
I work in a corp fleet department every 3126 we have has giving us problems they has giving us job security. I need some info on the wiring and fuel systems. I have one that will start on either and run at 1000 R.P.M but goes dead at anything under [email protected]
What did you do to fix this problem as I have the same issue.

Todd
Ramiro Flores

Los Angeles, CA

#203 Jan 15, 2009
gamboa wrote:
ser ayada por favor tengo un 3126 cuando lo dejo
tiempo sin prender tengo problema en prender lo
una o dos horas
si ve el sensor que esta en el lado del chofer. en sequida de la valve cover en frente de l motor. esta liquiando aceite?
charlie

Chandler, AZ

#204 Jan 16, 2009
1997 Beaver 3126 300hp cat, lost reading on dash oil gauge, need to know how to locate, oil sending unit. Understand there is a T fitting and the other gauge is still working. How do i find the unit.
Randy

Bellevue, WA

#205 Jan 16, 2009
I am looking at a 94 kenworth t800 dump truck that has a 3126 engine. The truck has 750,000 miles on it and the person that owns it now has only had it for the last 10,000 miles. He does not know if it has had any engine work done on it. He said that this is a 350hp motor, with a super 10sp trans. Is this engine and trany junk? Any information would help.
riemer6

Tinley Park, IL

#206 Jan 16, 2009
houw do you remove the plug where the block heater goes on a cat 3126

Since: Jan 09

United States

#207 Jan 28, 2009
2003 Freightliner Rollback - Need info?? 3126 cat-sh**!
not enough power to get out of it's own way on upgrade.
Starts and runs fine; sometimes engine protect light comes on and goes out w/ associated loss of power.
Suspect:
A) return check valve
B) ICP valve or
C) injectors not seated.
Not on scanner for codes.
I know HEUI pump needs over 850 lb.press.running.
Also already repl. sensor on top dr.side near valve cover.

Since: Jan 09

United States

#208 Jan 28, 2009
DynPro from Finland:
Poured over this site last nite 4 hrs.and your comments were a real education; thanking you already in advance.
Also was told by mechanic best way to set valves is not with feeler, but dial indicator. Is this correct?
Have a feeling that some of mine also are not exactly correct, as at certain RPM, they rattle.Better loose than tight.

Need help, please, on diagnosing above post.
Seems fuel starved.

Caterpillar 3126 Engine
#HEP13309225-9831 Family 3CPXH0442HDV
HEP fuel system

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