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spankyjr1
spankyjr1, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 2577
Experience:  I worked on all types of equipment semis,forklifts,farm,ect.
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Why would s60 loose run good at idle and loose power at 1500

Customer Question

Why would s60 loose run good at idle and loose power at 1500 rpm after an overhaul
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Customer: replied 1 year ago.
New injector,fuel pump, no air in the system, test ecm, timing is right, new check valve, no air in fuel system, good power to eat, new timing sensors
Expert:  Jeremy replied 1 year ago.
My name is ***** ***** I will assist you with your concerns.
What year is the Detroit?
Customer: replied 1 year ago.
97 12.7
Expert:  Jeremy replied 1 year ago.
You just eliminated 3/4 of the issues the newer ones have. Thanks for the follow up.
The only things that can cause it in your series would be improper valve adjustment, bad injector, or fuel regulator being bad as far as issues after overhaul and at such high RPMs. If your low end torque is good, then I would look at the fuel regulator first since that is always missed in a overhaul and then check the valve adjustment. The adjustment may have been done with the wrong sized J tool. I've seen this multiple times. In fact, I have a shop near me that uses the wrong tool all the time and I get a lot of their work because of that.
Customer: replied 1 year ago.
I already replace all six injectors, replace the fuel regulator and ran the overhead like 10 times
Expert:  Jeremy replied 1 year ago.
You used the 78.8 size timing tool? J39697 I believe is the number...
If you did that, then there is something else wrong...
You have good low end torque on the truck and it dies out at the higher RPMs only? No check engine light came on at all? I want to rule out SRS and TRS issues from the rebuild.
If no check engine, then I would look at fuel pressure issue. I would install a gauge and run a long hose to the windshield, rubber band it onto the wiper, and then drive it to see if the fuel pressure is dropping off or bouncing to indicate aeration from the head or cups. I'm presuming the head was reworked as well since the lower end was done, correct?
What was the reason for the overhaul?
Customer: replied 1 year ago.
Yea it has new srs and trs. New head. And preassure is good. And it was overhauled for lockup piston
Expert:  Jeremy replied 1 year ago.
Sounds like everything was done right on the engine side. If the work was done, overhead done, idles perfect, then the issue is got to be fuel related.
Did this truck sit for a little bit for possible contamination in the fuel? Did the fuel happen to get soot in it? If so, it will look black in appearance. Can you see water in the fuel by chance?
If the engine is good, that is all that can be left is a fueling concern...
Customer: replied 1 year ago.
Got 30 gal of fresh fuel in a bucket and went straight into fuel pump and straight to back of head
Expert:  Jeremy replied 1 year ago.
I'm going to have to opt out of this one for I would need to do hands on to see what is wrong with this one. You did all the diagnostics short of tearing the engine back down and rechecking work, measuring the block, etc... I'll open it up for other experts to see what else they have to check.
Expert:  spankyjr1 replied 1 year ago.
Hi, my name is ***** ***** you for your question.
Sorry for delay.
I have seen ambient air pressure sensor cause this.
Check reading on scan tool and compare to actual reading.
You will have to calculate from voltage to pressure and figure out how high you are above or below sea level.
Or just change out sensor.
Sensor looks like map sensor on cars mounted on drivers side of engine and hooks to nothing but wiring harness.
The sensor changes fuel mapping and timing based on outside air pressure.
The only other thing would be loss of vehicle speed signal you don't mention what kind of truck but some speed sensors back then had two windings try swapping leads from one to other.
Thanks in advance for leaving a positive rating. If you happen to need more help, this question will stay open for weeks.
spanky
Expert:  spankyjr1 replied 1 year ago.
I'm just following up to see if we resolved the issue or you need more info.
I would appreciate a reply so I know you are happy with my assistance.
Thanks
spanky

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