98 Town Car Running Rough

[mysticdub]

Hi Everyone

I have a 98 Town Car which runs very badly at times, I will try to explain as best I can:

When starting engine from cold it will run like a bag of bolts for about first 20 seconds and then will idle ok.

It is a little hesitant when trying to pull off from a standstill at times, even when engine is warm.

Quite rarely it will lose almost all of its power all of a sudden, this happens without warning. The engine does not cut out but it will only do about 20mph and it feels almost as if someone cut the throttle cable. Sometimes it will go alright all of a sudden, other times you have to turn ignition key off, wait 20 seconds then turn on and is fine.

When put on NGS it says all 4 O2 sensors are reading lean.

It has had following replaced, 2 x 02 sensors, 8 plugs, 8 coils, pcv valve, all filters.

Can anyone help?

Thanks

Ian.

[v8_dave]

Welcome! I would get a fuel pressure gauge on the rail to see what its coming up with, and also check the TPS voltage (but the TPS usually causes problems at certain pedal positions, not throughout the range). I'm still thinking fuel delivery from the lean codes, maybe an intermittent electrical fault of sorts for fuel voltage, or even a simple, yet rare, fuel pressure regulator issue.

Your on the right track!

[Fordace]

MAF sensors can get contaminated from a variety of sources: dirt, oil, silicon, spider webs, potting compound from the sensor itself, etc. When a MAF sensor gets contaminated, it skews the transfer function such that the sensor over-estimates air flow at idle (causes the fuel system to go rich) and under-estimates air flow at high air flows (causes fuel system to go lean). This means Long Term Fuel Trims will learn lean (negative) corrections at idle and learn rich (positive) corrections at higher air flows.
If vehicle is driven at Wide Open Throttle (WOT) or high loads, the fuel system normally goes open loop rich to provide maximum power. If the MAF sensor is contaminated, the fuel system will actually be lean because of under-estimated air flow. During open loop fuel operation, the vehicle applies Long Term Fuel Trim corrections that have been learned during closed loop operation. These corrections are often lean corrections learned at lower air flows. This combination of under-estimated air flow and lean fuel trim corrections can result in spark knock/detonation and lack of power concerns at WOT and high loads. One of the indicators for diagnosing this condition is barometric pressure. Barometric pressure (BARO) is inferred by the Powertrain Control Module (PCM) software at part throttle and WOT (there is no actual BARO sensor on MAF-equipped vehicles, except for the 3.8L Supercharged engine). At high air flows, a contaminated MAF sensor will under-estimate air flow coming into the engine, hence the PCM infers that the vehicle is operating at a higher altitude. The BARO reading is stored in Keep Alive Memory (KAM) after it is updated. Other indicators are Long Term Fuel Trim and MAF voltage at idle.

[Tman70]

Also, my favorites, the ECT and IAT sensors.

http://www.lincolnsonline.com/tech/00193.html