Engine codes 121 & 172 - not quite fixed!

Discussion in '94-95 5.0 - Specific' started by SIIaCanuck, May 15, 2016.

  1. SIIaCanuck

    SIIaCanuck New Member

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    For those who read my 'strange idle' thread, I'm looking for follow up advice. The original problem was 122/124 codes for an old TPS with a dead spot, which I replaced. RPM was hanging up at 1600rpm after along run, slowly dropping back to idle after 20-30 seconds or so sitting at a light.

    After replacing the TPS, I drove it for a couple of weeks and started getting a hunting idle. Then, on a hot day, after a long run home, she quit on me. Classic signs of fuel starvation (or vapour lock). Once cooled off, she started and ran like normal. Codes pulled were 121 (TPS voltage out of normal range), 172 (RHS O2 sensor lean) and 556 (fuel pump primary circuit fault). Fuel pressure was down at about 28-30psi at idle.

    I've put in a new 170lph pump, fuel filter, adjustable fuel regulator, Blaster 2 coil & new cap/rotor. I set up the fuel pressure at idle at 36psi (vacuum off). Timing is still at 10 degrees.

    The hunting idle is gone and the car seems to run and accelerate more smoothly. I cleared all the codes and drove the car to church this morning (20 miles total), with a couple of hammer down accelerations and a bit of time on cruise control.

    Pulled codes to check and got a 121 (TPS out of normal range) and a 172 (RH O2 sensor lean).

    121 - I'm thinking that the new TPS is giving a strange voltage. It's non-adjustable and the computer should set the idle volts at start and it seems to respond to throttle normally. I'll call the shop about the TPS to get their thoughts and maybe plan to swap out the TPS if there's a chance it's got a fault from the factory.

    172 - Injectors, O2 sensor, fuel pressure low (should I bump it up to closer to stock spec? 39psi?)? It's only the RHS so it seems unlikely that it's an intake air leak or MAP problem.

    Thoughts or comments? Other things to check?
     
  2. evilcw311

    evilcw311 Most Evil Mod! Staff Member Staff

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    Did you relearn base idle with the new tps??? If not then that's why your getting a tps code.


    This message courtesy of crapatalk!
     
  3. shadowblack5.0

    shadowblack5.0 New Member

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    Deleted crapatalk said this was my thread and it's clearly not.
     
  4. SIIaCanuck

    SIIaCanuck New Member

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    OK, some news. On the way home from work yesterday and today, when it was pretty hot out, I was hearing a bit of top end rattle that sounded like pinging, something I heard a while ago when it was hot. In cruise control at 75mph or so, when I hit a gentle hill on the highway, or fed her some throttle to pass a truck, she starts pinging on me.

    Timing is at 10 degrees so it shouldn't be pinging, even though I'd read that SN95 5.0 computers are prone to pinging, even at stock timing, due to the excess advance the computer gives at low load.

    So, four miles from home there's a country road I cross with a stop sign, so I figure it's time to see what is going on. In 3rd gear and 2000rpm I put the hammer down. I hear a slight rattle going through 3000rpm and then, somewhere between 4000 and 4500rpm, she noses over slightly (I'm a snowmobile guy so that's the term I use when you get a top end bog due to lean mixture) and the 'check engine' light comes on. 'Whoo Hoo' I shout, that's gotta throw a code or two.

    Sure enough, 181 and 189 show up with the 121 and 172. Lean both sides, rich limit reached.

    Now we're getting somewhere, sounds like MAF related issue so I pull the MAF and blow her clean with an aerosol MAF cleaner. It's got a K&N filter fitted by the previous owner so I gave it a really good few shots of cleaner and then let it dry out.

    Re-assemble, clear the codes and warm it up. Check codes and just the 121 (TBS idle re-learn didn't work so I'll have to work on that again). 172, 181 and 189 don't feature.

    Head out on the road. Cruise 4 miles over hilly terrain down to the stop, no sign of any pinging. Turn around and settle at 2000rpm in 4th and put the hammer down.

    All I got was a happy SBF having a bit of fun. Pulled through 5500 with no sign of anything, into fifth and nail her again. At about 0.5 mph over the limit (I'm a uniformed representative of Her Majesty's Canadian Government, so don't want to give the wrong impression :)), I figure I've got all I need and throw out the anchor.

    Roll up the driveway, pull the codes again and she's all clear.

    Thanks for all the help guys, very much appreciated. Now I can get on with the 3-link rear suspension and modified K-member I'm slowly putting together in the shop. And Cobra brakes. And H/C/I.

    I told my wife that I'm now much more likely to get a speeding ticket. Her reply, 'that's good news!'.

    She's a keeper!

    So is my wife :laughing5:.