Originally Posted by xkrjag1

Originally Posted by Darren_M

I would like to chime in if I may. Diagnostics is something I enjoy and everyone has given some excellent advise.
So here are some generic - all vehicle diagnostics -
Fuel trims, some manufacturers show them differently but if you have the ability to see short and long term fuel trims, you subtract one from the other and ideally you should be at or near "0". Short term is immediate correction and long term is correction over extended time. So if short is say minus 2 (-2) and long is positive (+3) then total fuel trim is Positive 1 (+1). Typically a + or - 5% total is considered a great trim. Once you start edging over 10% +/- then it can cause some driveability issues. GM for years used a 0 to 255 trim count range with 126 to 129 considered the "0" range. So a positive number is fuel being added and a negative is fuel being subtracted.

Fuel Requirements -
An engine is a pump, so it can only move a finite amount of air at any given moment. The computer knows this so at any RPM, engine temperature, throttle opening amount (demand), manifold vacuum (load), air temperature and barometric pressure a certain amount of fuel will have to be delivered. With a MAF, it measures how much air is actually going in and adjusts the fuel delivery accordingly. The computer also looks at other things it is running like EVAP operation, it knows that when the purge operation is operating a certain amount of vapor is being allowed in that the MAF does not know about and adjust acordingly. Like wise the same for the EGR (if applicable) and other items. It also looks at the O2 sensors after combustion to make immediate corrections and adjust long term corrections.

So having any one of those sensors slightly askew can cause fuel trims to be off yet not be bad enough to cause a code to set.

Now comes the tricky part, not all gasoline is the same. Alcohol content (for those who have to deal with it) can cause drastic changes. It takes more than twice the amount of alcohol by weight than gasoline for ideal combustion. Depending on where you live it can vary from 5% to 20% per gallon. So try to avoid if possible. Also gasoline companies use different additive packages and some do not add any at all. Try to stick with fuel that is Top Tier rated if possible and from a reputable seller. I avoid cut rate stations at costs as I have seen wide variations in fuel quality from them. Gasoline life expectancy is another problem. Typically gasoline in a vehicle has about a 2-4 week life before it has degraded to a point that it can cause drive ability problems. I know I just opened a can of worms there but you'll have to trust me on this as I see it a lot.

Engine Mechanical Problems -

This covers a broad range so hold on. A slightly pitted valve face/seat. Remember the engine is a pump so if there is a very tiny amount of leakage at the valves then the engine cannot move as air as it should. It can also cause the fuel to not mix completely with the air or cause exhaust to dilute the fuel/air mixture some time with gaps in the mixture to not have any fuel at all. This can cause fuel burning to be jumpy in the cylinder and can cause it to not complete combustion before the cycle is done thus felt as a misfire. Also problems with intake and exhaust plumbing can cause this to happen. Leaks, bends, restrictions, even an air filter can cause this too. Fuel pumps can cause problem misfires even though it is capable of delivering the correct pressure and volume. A good example of this was Chrysler when they went to w returnless fuel system. It was found that as the pump would wear, it's speed would increase to the point that it would whip up microscopic bubbles in the fuel (cavitation) These bubbles would start to come together at the end of the fuel injector rail (typically near number 8 injector on V8's) This would eventually cause the number 8 exhaust valve face to develop tiny pits that lead to a slight misfire. GM trucks would develop a misfire at idle on their vortec engine due to a slightly loose catalyst bed that at times could be a horrible misfire.

I could go on and on about the various causes but I think you get the idea. Check everything carefully, having diagnostic data available will make it easier but some things require more data than a scanner can deliver. I use my lab scope often when these get tricky, I can see misfires using the O2 sensors, or pressure transducers (sensors) on the fuel supply, intake and exhaust on my scope. And with the program overlay I can even tell which cylinder, fuel/air mixture, ignition, even piston ring problems and cam to crank relationship changes. SO even if everything checks out as being within range, if enough of those items are at one end of the range, their total may add up to the computer delivering fuel incorrectly and causing the misfire.

I might add that I am currently chasing an intermittent misfire at idle/off idle on my 1995 Vanden Plas. I have found a couple of problems and corrected them but not completely corrected the misfire.

Originally Posted by beaterbeliever

All ideas are welcome here lol. I absolutely know the gas quality, dealt with that with a cl65 I had. It would immediately have issues under boost with any cut rate gas, only liked Chevron for whatever reason.
​​​​​​Because of that car, I ended up being a stickler for good gas, regardless of how much more I would pay.
But, currently the gas in the tank is about 2 weeks old at the most. I just did the fuel pumps a week ago, fixing a low fuel rail pressure issue and a fuel sending unit sticking at half way point.

Originally Posted by beaterbeliever

Just to update, today I found a crack on the bottom of the EGR pipe, in the accordion area. Is it possible that this is the source to the current issue?
From what I gathered here in older threads, if I temporarily block it off until a new pipe comes in, I will get a p0400 code. But, it should run just fine?

Originally Posted by ccfulton

An EGR pipe leak won't affect the fuel trims. It is under positive pressure so will leak exhaust out rather than air in. I had the same cracked bellows exhaust leak for a long time and no issues whatsoever with fueling.

Originally Posted by beaterbeliever

New update. Well, definitely on the right track! After putting it all back together, trims are getting nearly there. Vehicles driveability has gone up considerably, though not perfect.
currently, now has a rough idle and lack of acceleration past 3500 rpm
​​​​​​after 15min, LTFT are as follows
At idle in park
Bank 1 : -0.73- -4.78
Bank 2 : 19.69- 25.20
At 1500 rpm
Bank 1: -0.2- 2.4
Bank 2 : 0.5- 7.8

In drive, 1500 rpm is similar to above

At 2500 rpmBank 1: -3.2- 1.4
Bank 2: 0.5-2.7

STFT on bank 1 varied through ranges above
Bank 2 went to 25% at any time below 1000 rpm, above 1000 rpm they would fluctuate between 0-11%

I switched mafs and it corrected bank 1 issues, so I'm assuming bank 2 has an issue now.
Just random thought here, but maybe bank 1 catalytic converter may be shot? It is new, but maybe because of the short runs and running like crap may have blocked it?? I am going to wait till it cools down and disconnect the 02 sensor to see if it can breathe. Any other ideas?

Originally Posted by Darren_M

OK, looks like at idle you have good fuel control on bank 1 now but bank 2 is definitely being commanded richer. At part throttle 1500 rpm bank 2 is still wanting some more fuel but not as drastic and at cruise it is even better. It would appear that you actually were dealing with a combination of problems all stemming from the injector melt down. I think you are on the right track with the testing but something is the back of my mind is pecking away and I just have an idea. So early on you mentioned this all started with and injector melt down/fire? How did you put the fire? out?? And if not a fire, does it appear that the original injector may have over heated and split? Right now I am torn between you having a vacuum leak on bank 2 which could be anywhere from the MAF to the cylinder head to possibly an electrical issue concerning an injector, wiring or driver in the PCM.
Typically a vacuum leak will allow improved fuel trims as you come off idle. When the leak is in only one bank then typically that bank is getting air that is not being measured by the MAF. That being the case then the opposite bank will tend to be rich and will show fuel trims as such. But if the vacuum leak is at an injector then it will be way off at idle and improve almost immediately on acceleration and then come back slightly lean at light part throttle. What concerns me is that you mentioned it will not accelerate past 3500 rpm? Got to ask, were you in gear driving or just sitting parked when you tried to go past 3500 rpm? A weak/failing injector driver (PCM) that cannot correctly fire the injector at idle yet can manage to do better as the pulse width (demand/rpm) increases is rare but not un-common. Also a wiring problem either on the supply or control side could cause this. Check those ground connections carefully and the wiring harness for overheat damage that may have weakened the wire/s Take a very close look for any vacuum lines, pipe connections and gaskets you had apart.

Man, if only you were at my shop because I would love to have my lab scope on it right now.

Originally Posted by Darren_M

OK, looks like at idle you have good fuel control on bank 1 now but bank 2 is definitely being commanded richer. At part throttle 1500 rpm bank 2 is still wanting some more fuel but not as drastic and at cruise it is even better. It would appear that you actually were dealing with a combination of problems all stemming from the injector melt down. I think you are on the right track with the testing but something is the back of my mind is pecking away and I just have an idea. So early on you mentioned this all started with and injector melt down/fire? How did you put the fire? out?? And if not a fire, does it appear that the original injector may have over heated and split? Right now I am torn between you having a vacuum leak on bank 2 which could be anywhere from the MAF to the cylinder head to possibly an electrical issue concerning an injector, wiring or driver in the PCM.
Typically a vacuum leak will allow improved fuel trims as you come off idle. When the leak is in only one bank then typically that bank is getting air that is not being measured by the MAF. That being the case then the opposite bank will tend to be rich and will show fuel trims as such. But if the vacuum leak is at an injector then it will be way off at idle and improve almost immediately on acceleration and then come back slightly lean at light part throttle. What concerns me is that you mentioned it will not accelerate past 3500 rpm? Got to ask, were you in gear driving or just sitting parked when you tried to go past 3500 rpm? A weak/failing injector driver (PCM) that cannot correctly fire the injector at idle yet can manage to do better as the pulse width (demand/rpm) increases is rare but not un-common. Also a wiring problem either on the supply or control side could cause this. Check those ground connections carefully and the wiring harness for overheat damage that may have weakened the wire/s Take a very close look for any vacuum lines, pipe connections and gaskets you had apart.

Man, if only you were at my shop because I would love to have my lab scope on it right now.

Originally Posted by beaterbeliever

Possible causes may be Vacuum leak, leak near injectors, intake-intercooler leak bank 2, and clogged catalytic converter, if I'm reading correctly and testing out correctly.​​​​​

Originally Posted by beaterbeliever

Hmm, the injector melted, burned through and dumped fuel. Bank 1, cyl 1 injector. Caused the fuel rail to catch fire, and melted that, took out 2 other injectors on bank 1. Resulting fire was put out with an extinguisher within 5 secs at most, as I was just idling at a stop sign when it happened.
I ended up replacing both the fuel rails and all Injectors with new, flow tested ones to rule them out.
I'm leaning to a vacuum leak, but not sure as to where. I took off the throttle body, elbow ,and blower hat and inter coolers today, checked those gaskets, found hairline cracks in the boots between the intercoolers and hat, replaced those with the originals since they looked good.and ended up here.

​​​​​​So, bank 1, where the fire occured, seems to be in line with normal operation. Now to find the issues with bank 2. Possible causes may be
Vacuum leak, leak near injectors, intake-intercooler leak bank 2, and clogged catalytic converter, if I'm reading correctly and testing out correctly.

​​​​​

Originally Posted by Darren_M

Hmmmm, as a rule an injector does not melt down on it's own unless the injector coil shorts but most of the time the driver will shut it down due to excessive current draw to protect it's self. Usually the culprits are a wiring short causing the injector to remain on full time, a failing or failed injector driver (PCM), or a fuel blockage preventing fuel to go through the injector (cooling) all of those could cause the injector to fail. Or it could be just a case of bad timing that an injector seal let go or the body of the injector split open causing the fuel leak and subsequent fire. In that case it is possible that the driver could have been damaged due to a short caused by the fire. Although such drivers are for the most part self protected and self healing eventually there comes a time in it's life when due to age and usage that all it takes is an incident to push it beyond the point of no return. A scope of the injectors would show what the problem is if it is in the injector/s and their circuit/s. Still keep checking for leaks. Over the years I have seen a few lower injector seals leak air into the intake ports only during certain times involving temperatures that either caused the seal to be non compliant and also due to rail creep as it expands and contracts.

Originally Posted by beaterbeliever

Yeah, I'm not sure exactly what caused it to fail, just that was what found left afterwards. Injector bottom was melted completely, fuel rail, and portions of the other 2 Injectors.

Oddly, still zero codes except a b1313 and b1314, battery circuit open? As the codes says it is, not sure exactly what that is though.

Originally Posted by Wight8

Exactly what i was thinking, I only freelance but scopes are where it is at for diagnostics, I- it's one of the frustrating bits of forum diagnostics that you can't see the waveforms.

Anyway back to OP's issues. Again the basic fuel trim data is pointing at an unmetered air leak on bank 2.
- Other things can cause problems on both banks and even more other things can cause rich trims - but rich trims at idle and OK at higher revs is highly likely to be that unmetered "pirate air".
For security check the live Lambda value of banks 1 and 2 O2 sensor 1. If you have a big leak then Bank 2 at idle will show greater than 1.0 maybe up to 1.2 (lean), then drop back to 1 at 2500rpm, Bank 1 should be 1.0 or very close to. Ignore both sensor 2s for the moment as it is pointless until the engine is running properly.

I do not know the characteristics of the SC or when the ecu enables boost, if it is producing manifold pressure all the time then we are only looking for an air leak between the MAF and the Supercharger. If it is only +ve above a certain rpm then a manifold leak would go from rich trims at idle (air is sucked in) to lean trims as air is blown out the same leak at higher RPM - this might account for your lack of power above 3500 - though I think that may be a separate problem.



Confused by this