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Old 06-15-2021, 04:35 AM   #1
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Default 10 mpg fuel trims at 12, and 14 percent

when i bought my 1997 Hardbody i got 14 mpg. it has been getting steadily worse. timing is right on the money, plugs, wires, rotor, cap replaced. had an EGR code at one point, cleaned that up, code cleared. had MAF code, replaced it, code cleared. replaced pre-cat O2 sensor, fixed a exhaust manifold-headpipe leak. fuel trims still high. have looked for intake leaks using carb cleaner, and starter fluid no indication of a leak. have replaced all injectors with brand new o-rings and seals, checked fuel pressure reg, tested fine, however i have no static fuel pressure with key off.
now i am getting an EGR code again, and a swirl control valve code. im at my wits end, the weird thing is that the truck runs great. thinking about pulling down the entire intake side and reinstalling with all new gaskets.
any advice will be greatly appreciated.
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Old 06-15-2021, 11:04 AM   #2
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Do anyway, if not yet: air filter, vacuum lines.
What's the timing set at?
You can do a smoke test to better check for vacuum leaks. Also do a compression test.

"any advice will be greatly appreciated" Use proper capitalization. :-)
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Old 06-17-2021, 09:58 AM   #3
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i do the air filter about every 12k miles, been replacing vac lines for 2 years now, timing is at 10 deg BTDC. i am a cigar smoker, tried it that way twice now, no indication. when i found my exhaust leak i tried something i saw on you-tube: attached a shop vac to force air into the exhaust, (with cold motor) and used soapy water in a spray bottle. it worked great. have been wondering if enough air might be passing thru the combustion chamber to work with the soapy water on the intake side? youd think at least one cyl. would have stopped with two valves partly open. does that make any sense?
haven't checked compression, but i will. it just runs so good, 85-90 on the interstate no prob. and rides smoothley around town at at low speeds. its making me Krazzzzy

Last edited by uwantitrightdoityourself; 06-17-2021 at 10:05 AM. Reason: spelling and additions
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Old 06-17-2021, 10:17 AM   #4
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hooked up my basic OBD2 scan tool today, this is the latest:
1/3 P0400, generic, exh gas recirc flow
2/3 P1130, other, manufacturer control
3/3 p1130, other, manufacturer control
Frz Fr:
fuel sys 1, OL
fuel sys 2, N/A
load, 29.8%
ETC, 140 deg f
shrtft1, 1.6
longft1, 12.5
MAP, 11.5
rpm, 975
VSS, 0 mph
after clearing codes, I/M readiness:
Catylist mon, inc
evap sys mon, inc
O2 sens mon, inc
O2 sens htr, inc
EGR sys, inc
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Old 06-17-2021, 12:28 PM   #5
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Open loop? Was the engine at operating temp? If so, that's something to look into.
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Old 06-17-2021, 04:17 PM   #6
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His truck is in Open Loop(OL), Deerhurst and his Monitors are not "set" or "Closed".

Was the check engine light on before you connected the scanner?

You'll need to repair these items, clear the codes and then drive the truck in stop and go traffic so that the I/M monitors can get their base settings and then compare them to the actual driving conditions and functionality of the truck's systems for their outputs. This will take some driving over several days. The object is to mimic a "normal working person's day drive into work". You start the truck, let it idle for about 2-3 mins as the engine warms up(the base numbers for exhaust and engine functions are being collected at this time by the ECM), put the truck in gear and start driving NORMALLY. No hauling ass & no excessive speeds. Just everyday stop and go traffic so that the ECM can collect the reference numbers and readings.

For the P1130 code. If you have replaced the vacuum lines. You'll need to trace each one out to ensure each one is connected to its proper connection on both ends of the small rubber hose. That would include the "vacuum gallery", the small metal tubes they connect up to.The P1130 code is vacuum to close the Swirl Valve Control Solenoid Valve, the intake runner butterflies. There is a brown colored plastic housing solenoid that controls this function. BUT the vacuum circuit needs to be correctly connected. its been my experience that this brown solenoid never fails. Also check the Vacuum Switch located on the inner fender well. That has a single vacuum line to it. I made the mistake and switched up two vacuum lines and got the P1130 code. Thought it was the swirl solenoid that crapped out. But while testing the solenoid. It never failed. I could always hear and feel a strong "click" while energized. It is also in my experience that Hitachi electronics that Nissan uses in the D21 trucks do not fail. I still have all of the original solenoids in my '97 HB and they have never been the root cause of any code that has popped up. Case in point, I am chasing a P1447 EGR code. I tested the black housing colored solenoid and it failed. Come back a few days later to test it again and it works perfectly. I had bought a replacement for Rock Auto. But the original solenoid still works when I tested it. I found that I had not touched the battery correctly and caused the solenoid to fail. But when the alligator leads were touched to the battery posts. A strong "click" was felt and heard. So that is why I feel it's never the solenoid. They are built with quality and made to last. In my humble opinion.

Check the Factory Service Manual(FSM) on pgs. EC-11 & EC-13. These pages will show you the component location and the vacuum line routing.

P0400 is EGR functions. The FSM shows the troubleshooting flow charts and component inspections to fix the problem.


The ECT temp seems a bit low at 140 degrees. I'm thinking it should be at 176 degrees with the truck fully warmed up after driving for about 20 mins.

Your RPM is high as well. Should be 750-800 rpm. So maybe an intake leak somewhere? Or just needs to be set correctly?

You only have 1 bank and it shows "OL" for Open Loop. So there are issues to be addressed before the truck will go into "CL" or Closed Loop". Where all systems are operating with no faults in their respective systems.

MAP is a touch high at 11.5 Mine reads at 9. But because your idle is at 975. I feel this is the reason.

Load looks ok at 29.5 Would be at 23-25% load while idling. Again, I feel it's the high idle. Is the A/C on when these readings were taken?

STFT is high. Should be closer to "0"
LTFT is high. Should be closer to "0"

Only a 4 cylinder. So no Bank 2 to read. If it was a 6 cal. The Bank 2 would apply. But has an Inline 4 cylinder. So Bank 1 only showing is correct.

So some investigating to do to close the monitors and get your mileage back!
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