94 GTS not run form many months, now will start but not idle unless given some accelerator and runs horribly rough producing massive clouds of black smoke.

Runs better, but still very rough with MAF disconnected.

Does that guarantee the MAF is the point of failure, or do the 'limp home' mixture settings bypass other sensors that could be faulty?

Any suggestions for further diagnosis?

Thanks,

Matt

 

I would check all fluid levels then I would start with the fuel system.

Fresh Gas
Injector Cleaner
Fuel Filter
Gas Tank Inspection

Then Compression check on all 8 Cyclinders

I'm not sure it's wise to run her without the MAF hooked up but again, I'm not sure.

Good Luck getting her dialed in.

 

Hi Matt,
There is a mode of MAF failure that results in the car running excessively rich. In this state the "limp home" is not activated, unless you disconnect the MAF, as you have done.

To confirm this is the problem, take off the upper engine airfilter housing, and take the filter out. Switch on the ignition, and pear into the MAF intake.

Wait 30 seconds or so, and you may see the platinum wire glowimg if it has this fault, which is thermal runaway. The other certain way is to measure the MAF output volts on pin 5 to ground which should be less than 2v with the MAF energised but engine not running, or about 3v with the engine near idle.

Let us know how you get on

 

The limp (home) mode failure of the MAF sensor is a CONTROLED rich mode. The injectors pulsed rate time is fixed at a rich map rate; no other sensors are affected. Borrow a good one and try it, pull the plugs if they are wet with raw fuel I doubt the MAF is the problem. .

I would check the fuel damper and regulators for failure by removing each vacuum hose to check for fuel; I would also check; the tempII sensor controls fuel timing as well as the full throttle switch erroneously called a TPS sensor. The procedure is in the WSM. Another problem for an excessive rich condition is leaking injectors.

 

Just a thought -- try disconnecting for a minute, and reconnecting the battery.

 

Matt,
All good advice.
Steve,
Long time...
Just dug up a verbal wiring diagram you posted for me many moons ago.
Thanks again. It might help Jason, though it does sound like a simple ground issue on his sHARk.
Matt, along with heinrich's suggestion to disconnect ...wait a few minutes...reconnect battery to do a brain reset.
I have to ask, did you jump start the sHARk after it's period of idleness?
If so how did you do it?
Heinrich's is the simplest test for starters. If it cranks back up take it for a spin 10 - 15 minutes to see if the idle smoothes out as the brain remaps off of baseline. If you don't have a good charge on the battery, trickle charge overnight, first. If you trust your voltmeter and it's reading lower than before, say 11v and under that could be part of the problem putting you in a fuel rich state. Then go to John Speakes suggestion, and finally Steve C's -more labor intensive .
If you didn't smoke something on a jump start I'd lean toward Steve's thinking along the fuel system. I'm guessing this may be one of a number of long idle periods and something in the system is gummed up.
Might try injector cleaner in the tank for awhile. (just a guess).

 

Havn't had a chance to follow up all suggestions yet. But to update, didn't jump start, using a new battery (so nothing fried?), no fuel smell at regulators, plugs heavily blackened (to be expected with rich mixture)....all of them (does that mean individual injectors probably OK?).

Will only run with MAF disconnected, so difficult to check for burn-off etc.

Will idle with MAF disconnected and run a bit rich, as soon as MAF is connected it dies unless given plenty of throttle.........and then produces masses of black smoke.

Thanks for suggestions so far........will continue to follow through each of them.

Matt

 

"Will only run with MAF disconnected, so difficult to check for burn-off etc"

Hi Matt,
You can just switch on the ignition, pear into the MAF inlet to do the check for the MAF thermal runaway fault. The engine doesn't need to run.

As the car has been standing a long time, it could well be just a poor connection somewhere.

Limp home mode forces the fuel ECU to give two fixed injector pulse widths, one at low revs, the other at high rpm. The car won't idle properly because there is too much fuel for a proper idle, but it will get you home. In this mode, it does ignore temp sensor 2 and other sensor inputs as Steve said.

Good luck !