astvic

I had the "not running on all cylinders" issue.
Everything is fine today

My conclusion was the COILS and IGNITION MODULES (also mentioned earlier).
With new coils the car suddenly changed dramaticly.
Much more power in the ignition !!!! totally new engine expirence.
Try to change them with some new once. If they only perform let's say 50% (you can only measure there performance only if they are electrically intact or not) then there wouldn't be enough "power" to ignit. (just my therory)
After that I changed the ignition modules. The bad coil can and will damage the ignition modules (from what I have heard).
My coils was the original onces (18 years old) .

Just an input.
Don't forget to exercise the spark plug connectors !!!!!!!!!!!
All mine looked good and also measured correct (3 ohm), but when I took under specail care, two of them broked. Just as easy as a boiled sausage. Afterward I could see that they actually was broken. Only 15% of the plastic in the 90 degree angle was intact. (if you now what I mean)

John Speake

Hi Stan,
Don't forget that until the engine water temperature gets up to around 70C, the car is running open loop.
this is a good time to be able to properly evaluate the MAF as fuelling is dependant on MAF calibration in this phase of running. At very low water temps there is mixture enrichment from the LH, but from about 40-70degC the engine should run well.

Cat equipped cars can tolerate quite bad MAF ageing when water temp is high enough for the O2 loop to take control. It can cope with quite severe MAf ageing once fully "adapted". (say up to 10 % or so.)

The 3% that Jon mentioned is the point at which throttle response and WOT power can suffer, because under those situtaions the O2 sensor is ignored, and the car is again open loop, and MAF calibration is critical.

In your case I would consider the possibility of a bad injector.......

ew928

His year old gas has 'appreciated' monetarily by a lot.

Stan, think you're running diesel in that car after aging for a year.
Good luck with getting her running.


Any chance to drain tank and run a few gallons of the $4.70 stuff in there.
Cheapest I saw around Lime Rock was $4.59 for premium.

Heard the classic motorcycle guys were having the worst fuel related problems till they put in fresh gas.
Cheapest low cost fix if that is part of the problem.

WICruiser

Unforyunately adding Stable after the fuel has aged for a year doesn't do much good. Once the fuel has degraded there is not much you can do other than get as much out as you can and dilute with fresh fuel.

ew928

Remember at SITM few years back the fuel pump was powered up and an extraction fuel line attached to the passenger front fuel line (the place where people attach aftermarket fuel pressure gauge).
The pump then pumped fuel from tank out.
Something like that.
This way any questionable fuel in the rails and the line from tank to motor is also pumped out.
Don't know if this helps.

Mrmerlin

if your trying to pump out bad fuel i would NOT use the fuel pump to do it, just remove the rear pump cover then the soft line to the fuel pump , the fuel will flow out slowly as its going through the screen filter, , eventually most of the fuel will drain out leaving about 4 to 7 ozs depending on how high the rear is. new fuel pumps and filters are very expensive ( no need to pump a few gallons of bad fuel throught your fuel system)

Stan.Shaw@Excell.Net

I would think a bad injector would be constant, right? When I disconnect the MAF, the car idles as good as it ever has. This is true whether I have the recently rebuilt MAF in place or the old (not known to be bad) MAF in place.

Based on what you are saying it seems that the LH is not properly adjusting fuel when it knows how much air is passing through the MAF, but when it doesn't know, it presumably uses defaults that work.

Stan.Shaw@Excell.Net

Why would disconnecting the MAF mask such a problem? While I know new parts can go bad, all the wires are new. Also, since I checked the plugs and found them all to be similar, and good, it would seem they are all working equally.

John Speake

Hi Stan,
Yes you are correct.

Sometimes LH can fail so they think the WOT switch is always operated, resulting in over fuelling tec.

Can you swap in another LH ?

Stan.Shaw@Excell.Net

Thank you for the thought

No, I don't have another LH. I might be able to convince a neighbor to loan me one. I don't know how quickly an LH goes bad, but mine was tested just a few months ago and was fine then.

Stan.Shaw@Excell.Net

If it were over fueling, would this possibly lead to a fault being detected by the ignition circuit relay?

John Speake

No, as the over fuelling would be the same for all cylinders, so exhaust temps would be equal, and the igntion protection circuit would not be triggered.

Stan.Shaw@Excell.Net

Ok, thanks. Perhaps with the MAF disconnect the EGTs aren;t monitored then. So if one is bad, the disconnected MAF would prevent the erroneous EGT from being reported.... Not sure, but I will try disconnected them next and then reconnecting the MAF.

I just hope I remember this stuff in the future

worf928

I disagree John. I think that if the over-fueling is massive the lower combustion a/f limit can be reached periodically in one or more cylinders. The mixture is too rich to ignite properly. Even under perfect 'factory' conditions the cylinders will not get exactly the same amount of fuel.

I base my opinion on direct observation, troubleshooting, and repair of a 90GT a few weeks ago. The o2 sensor and MAF were both bad. The motor was running so rich that the protection circuit triggered. The obvious explanation is that the over-rich condition coupled with other uncharacterized non-optimum conditions (such as perhaps bad spray pattern on one or more injectors) quenched one or more cylinders sufficiently to cause a temperature differential between the EGTs.

ew928

Rich A/F enough to have visible black exhaust emissions?
Saw that at SITM with the sick Texas 928 spewing black smoke from running way rich.