Contour Enthusiasts Group Archives Forums Modifications Forced Induction problem w/ Simon's car

Been working on Simon's car for a bit, and we can't seem to find a solution to his problem.

The car stumbles and bogs down at low RPMs and runs very lean up until about 5k rpm, then everything is perfect.

We've cleaned the MAF, changed plugs, changed the fuel filter and checked all the electrical connections.

We're puzzled as to what it is, any ideas?

-John

Would seem the computer is having problems calibrating the proper amount of Fuel and is then going to Open Loop at WOT. What happens when you floor it? Does the problem go away or progress to kill the car? Clear the PCM by unhooking the Battery and check the upstream O2 sensors.

i have heard of bad injectors causing the same type of problems. what year is his car?

After driving the car home from John's house maybe I can add a little more info.

I have an air fuel gauge and if the car is idling, it is on the stoich side of the lean scale. As soon as I dip into the throttle the gauge goes of the scale to the lean side. The farther you open the throttle, the leaner it gets and the more it struggles to gain rpm. If you gradually ease off the throttle it gradually seems to make more and more power as if the mixture is getting closer to stoich.

Also, it seems as soon as the FMU starts bumping up the fuel pressure it rectifies the problem and the car runs beautifully.

I guess what we are asking is: What would cause the car to run extremely lean?

I'll reset the computer tomorrow, and see if that helps.

Thanks

MAF?

A vacuum leak?

Originally posted by fst4dr:

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I have an air fuel gauge and if the car is idling, it is on the stoich side of the lean scale.

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That screams bad O2 to me. Once the car is warmed up (well, really the O2 heater), the signal should oscillate around 0.45V (STOICH) any time the car is in closed loop and especially at idle. This should occur within 30 seconds of turning the car on. If the O2 is bad, but the PCM hasn't thrown a CEL yet, it will be using bad information to set the FI pulse. Once it throws a CEL, it will disregard the bad O2 and use the good one to set the FI pulse for both sides. That's enough to drive around on to get a new O2, but not something I would want to do if I was blown.

Got an OBD-II scanner handy to monitor that sensor (the one that the gauge is hooked to) or Pending Codes? I suggest checking the wiring for the O2 and maybe swapping in a known good one.

Thanks for all the ideas, but the problem seems to have worked itself out

All is good for the time being, but I'll be keeping my eye on it and hooking it up to an OBD II ASAP.

Thanks

A few things to check:

Fuel pressure - Failing fuel pumps can go bad in steps... doing bad one day, then good the next until they finally kick the bucket. Make sure the Vortech pump is wired in line and making good connections. If you used the wrap over connectors they included (first off, shame on you) check to make sure they're still making good contact.

Vacuum - A leak can really "F" up your fuel pressure, especially while running an FMU. (usually this would make you fat across the board though)

Fuel filter - Could be dirty.

Injectors - Could be dirty/faulty.

Originally posted by PA 3L SVT:

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Originally posted by fst4dr:

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I have an air fuel gauge and if the car is idling, it is on the stoich side of the lean scale.

---

That screams bad O2 to me. Once the car is warmed up (well, really the O2 heater), the signal should oscillate around 0.45V (STOICH) any time the car is in closed loop and especially at idle. This should occur within 30 seconds of turning the car on. If the O2 is bad, but the PCM hasn't thrown a CEL yet, it will be using bad information to set the FI pulse. Once it throws a CEL, it will disregard the bad O2 and use the good one to set the FI pulse for both sides. That's enough to drive around on to get a new O2, but not something I would want to do if I was blown.

Got an OBD-II scanner handy to monitor that sensor (the one that the gauge is hooked to) or Pending Codes? I suggest checking the wiring for the O2 and maybe swapping in a known good one.

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i agree with ya on this one for a few reasons.
1) when I installed my air/fuel ratio gauge, I had unplugged the o2 connector to do my splicing. a buddy of mine, who actually did the splice, spliced it in a different area - therefore not needing me to disconnect the o2 connector. my air/fuel gauge reacted the same EXACT way as that - until one day I was at a fellow ceg'ers house and noticed my friggin o2 unplugged. plug it in, a few hours later, the cel was gone - everything was fine in air/fuel ratio world.

2) this happened again to me two weeks ago. I detailed the engine - getting too much water into the o2 connectors, having the o2 sensor reacting the same way. a day in the sun with the hood open, dried up the connectors and the air/fuel was fine after that. (dummy me forgot to run the engine after spraying it down. )

anyway - both instances, it was related to the O2. Both instances, the air/fuel ratio gauge - reacted the same exact way to what you describe! HTH.
Later!