OP, aside from the hoses and metal tubes and fittings of the air pump connections at the exhaust manifold, the check valves themselves can be leaking and need replacing. I suspect when you scan for long and short term fuel trims you will find one or possibly both banks reading high (rich) so replacing any of the associated air pump parts may be necessary.

My metal fitting the check valve is on had a small crack you could only see if removed and carefully looked at. It caused a significant problem resulting in that bank to run rich to the point it killed the CAT (partially blocked its flow). That part is not available, so I had it TIG welded. I also installed new check valves.

Your system may be fine but if and any section of exhaust pre 02 sensor needs to be checked for any leaks.

Good to check injectors with rail off....new parts can also be bad. There is a reason you have gas in oil which you need to find out. We can only offer suggestions from this side of the internet based on your descriptions but unfortunately do not have eyes on what you can see and find

Good luck

 

Thanks to you both Chim and Fred, I"ll do what both of you said, will change the oil and filter on Tuesday when the new filter come to my place and see what happens and get the old one to lab for analysis

Also, will check air pump valves for leaks, was in garage a couple minutes ago and didn't see anything cracked or loosen connections, inspected it closer, so if you can just send me approximate values for short and long term fuel trims and I will pay attention later in a drive with my scan tool

Will check for other exhaust leaks pre O2 sensors on both sides and see if anything is in problem, I have a problem with the error code on passenger side for O2 sensor slow response for a while and recently I managed to remove the old one and put new, it was a very tough challenge, but I succeeded, put on the driver's side also new one although there was no presence of codes on scan tool

Recently when I was in garage I remove the rail bolts and rise the rails a couple of inches in air on with injectors attached to see if any leaks, primed the pump with the key couple of times in a row and let a sit for a couple of minutes, didn't see any leak, not a single drip, if I did that correctly and understood you right. Although I saw that I have a quick fuel pressure loss in about 10-15 minutes after I shut off the engine after drive or idling. There is significant drop from about 38-42 PSI st the key ignition on and at idling to 10-15 when I shut off after about 10-15 minutes, anyway in no more that 20 minutes. Is there a possibility for a bad check valve in fuel pump and because of that problem with extended warm cranking after drive when shut off and sitting for a while and does that can cause this oil and gasoline mixing?

 

I don't think the FP drop after key is off is a problem. If wih key on it snaps to about 43 then drops about 5psi after prime and otherwise stays steady increasing as you rev the motor its fine.

Often the longer cranking is due to a faulty FPR but I believe you said you replaced that. Pull the rubber elbow off FRP after you shut the car off. If there is any sign of fuel in that rubber nipple the FPR is bad

Ideally Fred can advise what "normal" short and long term fuel trims want to be. He is way more versed on data than I am. I do believe they need to be close to same on both banks vs 1 bank reading higher which indicates thats the side of motor the issue would be.

It was a good idea to replace both front 02's even though 1 side was bad. Generally, they have a live span of 50k mi before they become "lazy"

 

Thanks Chim on fast reply again, I have a quick drop of fuel pressure after the car is shut off, in about 10 minutes goes to 10-15 PSI and remains on a that level for a while. Beside that, I didn't saw any other abnormal values in fuel pressure during the idle and on prime. When I remove the vacuum line from fuel pressure regulator when idling I got additional about 8 PSI more.

Don't know what's the problem with that extended warm cranking after shut off and sitting for a more than 15 minutes, sometimes fire at first in that situations, sometimes, more often don't often in a second, but need a 3-4 secs of cranking. When I press the pedal to the floor and enter the clear flood menu it fires off instantly.

The injectors are all new, Standard Motor Products, the fuel pressure regulator is also new, ACDelco, because on the old one was diaphragm leak problem, so I replaced it and the vacuum line end which attaches on regulator nipple get harden of gasoline and cracked when I was removing it when FPR changed, so I put the new part of some garden plastic elbow hose on that end of vacuum line and reattached back on new FPR, but maybe it's not the same size, diameter. If you are talking about that rubber elbow? I just see the vacuum suction from that repaired line when I remove it from the FPR during the idle.

Hope to hear from Fred for these values for short and long trims to better inspect these parameters while in drive and more precisely know if it is in normal, acceptable ranges.

However, today I won't drive the car as I said earlier in previous post, so I just tried to see if the injectors are leaking with putting the rails off and priming with key ignition on couple of times and put everything back on, after didn't see the drips of leaks after couple of minutes in which I see the pressure drop.

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My FP drops like yours after the engine has been off. Been that way for over 20 years. I do have a Walbro 255 LPH FP though. That has never been a issue for me relative to starting or driving. FP is otherwise spot on

I always wait for the fuel pump to prime before turning the key to "start". It lites off immediately

given your parts replacement yet running rich to the point you smell gas in the oil my guess is you have some vacuum or exhaust leak pre 02 causing PCM to read lean thus dump fuell.

The fuel trim log will show what bank that is by having higher #'s than the other bank...assuming both banks don't have a leak but just one. In normal conditions each bank should have about the same if not equal fuel trims

You would be surprised how small of a leak will cause a issue. My metal pipe fitting for check valve was cracked but "under" it so I could not see until I just wiggled it and saw it move so removed it and could see a VERY small crack where the tube part was attached to the thick threaded part. Also a small pin hole in header. Both those issues went unfound for over a year causing a struggle to pass smog and eventually clogged (killed) the associated CAT. Fuel trims were much higher on the leak side. I would REALLY look close for anything that could leak associated with any vacuum line, exhaust gasket, air pump system.

 

Thanks Chim again for your info about how quickly your fuel pressure drop after shut off. I will inspect again that part because when I checked yesterday injectors, they are not leaking after priming a couple of times and wait after for a 10-15 minutes, the time period I mentioned before when the fuel pressure drop. Still don't know what can be the culprit of that warm extended cranking problem after sitting for more than 15 minutes after drive. As I said earlier, checked the fuel pressure regulator, everything correct, there's no gas leak on vacuum port, don't smell anywhere near rails external gas, don't see any cracked hose etc. I doubt that something with return line is problem like bad fuel pump check valve or maybe the feedline, some cracked or leaky parts of hoses or connections in tank itself from where all starts with fuel.

Yes, me too, I always check for prime that 2-3 secs and after that crank.If it is not hard to you, just send me your model of fuel pump which part number is or some weblink from which you bought it, in case that I have to buy a new one. Is there a big deal to put the tank down and inspect in order to confirm this problem or you made a cut under the carpet panel and made a trap door? I am not interested in cutting anything, not so nice idea from my view.

I will inspect the leaks tomorrow more precisely and detailed again. You mentioned to pay attention particularly on vacuum leaks or exhaust leaks and AIR pump check valves so I will do it like you said, suppose that something is very small so can't be detected easily.

Still waiting for the advice from Fred for short and long trims just to know what to expect when I put the scan tool and observe it during the drive, hope to hear from him soon and help to resolve this because he knows very well and have great knowledge and experience.

If I understood you well, the best solution is to inspect metal fittings for check valves and if needed to remove them to see if everything is tightened and seats correctly without any leaks and cracks. One thing to note is that I see hear the AIR pump sound each time when I fire the car for a little longer than before and can't remember that I hear this sound each time I start the vehicle before, now it's constant on each start and in compare to before a little longer duration than before and also when I shut off the car each time I hear some short vacuum suction which lasts about second at the time when I shut off the car, don't know if that is regular, but can't remember that sound from earlier time.

 

It's been at least 20 years since I put in the fuel pump. I bought just the Walbro, not the whole pump assembly. Since I have heard there are clone Walbros that were pure crap so be careful on source you buy it. I can't remember where I got mine, but I did have to cut and solder on a different connector for it to work.

I have a B Body (96 Impala SS) so different tank than what you have. I can drop my tank without much effort but my understanding on F body it's a more tedious process (exhaust in the way?). I have seen F body guys hack cut a access hole in trunk, not my thing.

Maybe that vacuum his you hear when you shut off motor is your air intake?? Is it stock?

The elbow on stock intake has been known to crack on bottom where it attaches to TB

If you scan car now for fuel trims and whatever the #'s are if one side is reading consistently higher...that's the bank that has a issue likely a vacuum or exhaust leak pre 02

 

Thanks Chim for comprehensive and precise answer and help as usual, I will look only for Walbro fuel pump unit, I have also thought only about the pump itself, not the whole assembly. I will look carefully for that you said to find the real genuine Walbro, not the fake copy.

Yes, on F-body as I see I have to remove the part of exhaust which lies beyond the tank for removing the tank and other option is to cut the trap door back under the carpet panel rearward, but not really interested in cutting the chassis of the vehicle, it wouldn't be tight and correct as the stock one now.

Yes, I hear a short 1-second hiss after I shut off the car identical sound like when you take a breath a second before you go to dive in the water when swim. I hope it's normal and regular.

Checked the rubber elbow intake, it's on it's place and without cracks, at least I can't see or touch it anywhere on the hose from the MAF to the throttle body entrance.

I found today the little crack on some of the air pump connections on the passenger side where metal tube connects with the rubber hose (the one I have the slow O2 sensor response error code for a while) and replace it with the new rubber hose and tighten it up, so I think that was the culprit.

​​​​​Also, I checked with carb cleaner on cold engine all the other connections where vacuum hoses connects, PCV valve, fuel pressure regulator and EGR valve behind the intake manifold, but no change in idle and engine RPM's when I applied the cleaner, the idle is all the time smooth and seems quiet and like it should be.

​​​​​​Hope to hear anything from Fred also, as I didn't have any intention to say anything wrong for him in previous posts to get angry on me, when I said he is a almighty great specialist, comparing with me, as I am listening to you very carefully and really appreciate and respect your help, participating and everything here when all of you join and communicate.

I will look when I take a car for a drive tomorrow or on the Wednesday for a oil warmup and oil and filter change and I will take the sample for analysis as I found the authorized laboratory in my city which can test the oil.

 

STFT should fluctuate between rich & lean. Depends on what software or scanner you have is if it reads in % or .xxx (.100-.900). Some offer the ability to show either format, % or .xxx. Basically both banks should be within 3% IIRC of whatever measurement value the data shows.

Again Fred is way more versed in understanding data than I am.

Your discovery of leaking hose on air pump may have resolved your issue if its the only source. Scan and see if the values of your STFT and LTFT are basically = readings between the 2 banks. They will fluctuate up/down in STFT but ideally within the same parameters as each bank IIRC.

 

Thanks Chim a lot again, i will observe it in a drive tonight when I go with car to the downtown. I will carefully and detalied look at the values you are talking about and their differences.

I hope Fred is not pissed off and will jump in and help as always, as I didn't mean anything wrong and not joking when I said he is a truly specialist in comparison with me as a total novice, it wasn't a joke, I really and honestly appreciate your help and advices and have a full respect for you guys here.

I hope so also that was the only leak, I checked another places also, I will put the link to see here and tried again on a cold engine first fire in garage and applied the carb cleaner on vacuum hoses and other connections all I know, you will see the first rubber hose on the passenger side that is new one, that was one I replaced yesterday, had a crack underneath where connects to the metaltube and couldn't see it easily just like you said, identical situation.

You will also see on the video my dashboard clusters and oil pressure gauge light and you can also observe and hear the sound of engine work at idle first fire, not so hot, maybe a couple of minutes after starting, I don't have it experience to claim that it's okay sound of engine work, but seems correct to me, once I revv the engine oil pressure gauge jumps in accordance with the jump of RPMs instantly

I found the authorized lab in my city and I will tomorrow or on Thursday change the oil and filter once they opened up again and take the sample on analysis

https://files.fm/f/fd6758qwp

 

Your dash OP gauge "may" not be accurate. I have a Autometer OP gauge using the port above oil filter. Your motor sounds normal in video. Good you found some lines that were suspect for leaking (old, cracked)

Your oil analysis will tell if there is a higher than normal metal particles in it.

You can try 10-40 oil to see if your oil pressure improves on your dash gauge.

 

Thanks very well Chim, I checked with the analogue gauge on the place of oil pressure sensor on the rear of intake manifold and there was a result of 4-5 PSI. I can do what you said and try the measuring downstairs above oil filter area on the auxiliary port beyond the oil filter if there is also one like on the earlier models 93-94, as they have the oil pressure sensor in that area.

In regard with this oil analysis, if you have any note or suggestion, what precisely to demand from lab to check for me, just type me please, because here in my country unfortunately there are no many specialists, labs and generally low level of knowledge about US cars, they told me to bring the oil sample of 6-8 ounces and they will inspect it, do the visually look, test of viscosity on 212 F temperature and flash and fire point, that what they told me, when we spoke on the telephone about it, but didn't mention metal particles, as I said them that I am in doubt that my oil is diluted with gasoline

Okay, I will try, this time I changed the manufacturer of stock 5W30 oil, so will try with the other one and I put the WIX 51069 oil filter last couple of times, I think that can't be a culprit of this problem with low oil pressure, before I used a ACDelco PF454, but there is no more on stocks here, so the best replacement they offer to me is WIX.

 

WIX is an excellent filter. Only ones I use.

Low oil pressure, which you have verified with another gauge, is typically a result of worn crank & rod bearings. A thicker weight oil is often used to help fill that wider gap however its just a Band-Aid if the bearings have worn that much but will extend the life of the motor. Some rebuilt motors like my 383 were done with slightly wider bearing clearances to allow for a thicker oil wedge between the bearing surfaces. I use 20-50 oil per builders specs. But this is intentional, not as a result of "bearing wear". The old air cooled Porsche motors were set up to use 20-50 wt oil for this wider bearing clearance reason.

For the oil analysis I don't know the specific process they test but they can see how many particles per million of various substances (aluminum, copper, etc) and high measurements of those are from bearing wear. They also can see how much the viscosity of the oil has decreased (ability to lubricate) and dozens of other things.

This is one of my LT1 motor oil analysis reports for my 383 motor to give you an idea of what it reports

 

Thanks Chim again on lightning-fast reply, I will continue with the WIX filters, as I haven't had any complaint not a bad review on them so far.

I hope so my engine is not in problem, as I haven't planned that overhaul in a while since it sounds pretty normal as you saw and heard, hope maybe oil pump pick-up tube fell off or something else, I don't know else what nonsense can be problem, because it's seems strange to me when I apply the brakes hard during the drive suddenly and each time at some speed when I suddenly hit the brakes hard the cluster gauge of oil pressure bounces to the zero than go to maximum after the maximum PSI and goes back 20 PSI when I continue cruising at 1500-2000 RPM

At last, if there would no some easy fix, I will try like you said with the thicker oil like on old Porsche and Beetles generations with air cooling

Nice, I know have all what it takes for them to see in lab in my place and do the same analysis, thank you very much for this picture friend.

 

your low oil pressure reading by 2 different gauges and your comment that when you brake hard your oil pressure drops suggests the oil pick up has come off the pump, assuming you have 5 qts of oil in the motor.

I believe I suggested using a snorkel camera through the oil drain plug to see if in fact the oil pickup has come off. If it has not then maybe the oil level sensor located on the side of the pan is bad giving false notice although that sensor is for "oil level", not "oil pressure". Is it the oil level light that comes on when you brake hard or does your oil pressure gauge say that?