Fuel injector or O-ring leak??
 

Greetings, GM 3400 wont hold fuel pressure, leaks down within a minute or two with pressure gauge attached, smell gas hard warm start, will crank a dozen times to fire, smoke like a flooded engine occasionally, recent high rev at start cold etc. Changed FPR with no change. Planning on tearing it down, will start with and O-Ring kit. Can a bad O-ring cause gas to flood engine? Mechanic seems to think it is a bad OR , said he would replace them and if still leaking would clean them?? Didn't sound right as he didn't even mention a new injector. So I figured I would do it lest he have the vehicle for days. I assume I will need a new gasket for the plenum? Will check for presurised leak once I pull the fuel rail, assuming this will indicate a partially stuck injector. I am assuming it is a partially stuck injector as it runs fine and idles fine, start good when cold "rich mixture" Does this sound like I'm on the right track? Never worked on injectors but it looks like something I can do if my back holds out:) Any info would be much appreciated.

If it is a bad O-Ring, it will usually leak externally. If he is talking about the injector o-rings, those will either leak fuel externally also, or cause a vacuum leak. The only thing that can cause fuel to flood the engine are the injectors or the regulator, which you just replaced. The computer can also command too much fuel, but it should also hold fuel pressure with the engine not running.

I would suggest having the car scanned for any possible codes. Even pending codes won't trip a light, but it will give us somewhere to start.

Thanks guys, Thats kind of what I figured, that the internal leak was probably an injector. The mechanic wanted to work on it at night, probably after work moonlighting:) but I wondered how he would get parts after hours, he seemed convinced I just needed Orings. So glad I checked with you guys to confirm. I have scanned it with a cheap hand held and no codes , just know I have a flood condition and it will need tearing down, pretty sure I can find which ones are leaking at that point. I will change all o-rings while I'm in there. I will let you all know what I find, Thanks again.

Take a can of carb cleaner and spray it around the injectors with the car running. If the engine changes idle, then you found a leak.

Thanks Mike , I will try that in a minute, but that would only indicate an external leak, right,? it wouldn't tell me whats going on at the bottom end. Any idea on the kind of O-rings to buy and gasket?

I see you are from NY. I am from the Utica area actually Remsen , moved to Michigan about 30 years ago.

Ok sprayed wd arond all injectore, no change in idle. Got a code though, 0102-Mass or volumn air flow circuit low imput. Any ideas on that one, Thanks

Checked voltage at MAF sensor, over 12 Volts. Need a scan tool to check its operation. would a parts store do that?,Could that cause a the gas problems I am having, I mean except for the pressure drop.? thanks

If the voltage at the MAF sensor is 12v, then that is fine. The sensor needs 12v to operate. It then sends a signal to the PCM telling it how much air is coming in. More than likely, you need a new MAF sensor. Once that is replaced, use your scanner to reset the PCM and restart all diagnostics.

I believe once the MAF is replaced, your issues should go away.

My plan is to use a cleaner on the MAF to see if that helps first. But I still have the leak down issue to deal with, the gas is going somewhere, Thanks again

Have you checked your oil level lately, if you had a leaky/stuck injector then you'd start seeing the oil level rise.
I've never heard of a bad/failing MAF actually effect fuel pressure, the only thing I know of that effects the fuel pressure would be the fuel pressure regulator, stuck/leaky injectors, or a hole somewhere in the fuel line.
If you want to see if any are stuck, then pull the injector electrical connector off, then get you a 9v battery (do not use the cars battery), and for a second touch the - and + form the 9v battery to the injector electrical connectors, and listen for a click, if you hear a faint click, then the injector is not stuck, but it could still be leaking internally.
If the injector is leaking internally, then replacing the o-ring is going to do nothing.

NOTE: if an injector was leaking too bad internally, then you'd expect a cylinder to misfire, and the fact that you smell gas when you start the car, has me leaning more towards a small pinhole somewhere in the fuel line.

No, but a bad MAF might cause a gas smell/hard start/easy start if the PCM is dumping too much fuel.

As I said earlier, the MAF issue needs to be taken care of first.

I agree Mike, because of the MAF code, that would logically be the first thing to address, I was just giving him some other things that he can easily check if cleaning, or replacing the MAF did not resolve the issue.

Even though it may very well be his MAF sensor, I admit I am still a little confused as to how a bad MAF could cause a loss in fuel pressure, I thought the only things that can seriously effect fuel pressure are the fuel pressure regulator, fuel filter, or the fuel pump.

Nope, your correct. MAF has nothing to do with fuel pressure/volume.

I am going to address that MAF tomorrow. All the injectors have the cliclking sound, the fact that it runs so well makes me think its just leaking enough fuel to effect the starting, as I say ,in the winter or when cold it starts normally and once running I see no engine performance issues ,either at idle or high rpm. Never noticed any gas in oil. It appears the injector is working but not closing completely, thats why I thought it may just be partially stuck or just a bad one. I appreciate the feed back from all of you and will keep you updated.

If it is kind of sticking a little, perhaps you may try some fuel system cleaner to see if that helps. My personal favorites are seafoam (Works so good, it tends to finish breaking stuff held together by junk) or techron (The safer, but still effective alternative).

Next time you think its going to take awhile to start, try this... hold the accelerator down 1/8 of an inch and try starting it. If it starts right up and you let go, does it almost die or does die?

Interesting discovery today
 

Just tried that Mike,What was your idea there? no difference as usual, after sitting a while it turns over about a dozen times before firing, I assume it takes that long to build up fuel pressure after leak down, but thanks, we'll get this yet.

My discovery happened when I went in to Advanced auto parts to get some supplies, MAF cleaner, sea foam, air filter. I was telling him about my code , then I asked if he had a code reader and he said yes so I asked if we could double check and compare mine to his. He could find no present codes but found 18 past codes, He had a lot better reader than I but he said try yours again and sure enough mine came up with the 0102 MAF sensor again?? Suppose I need a third opinion? Any way I cleaned the MAF, new filter, Sea foam. Checked for code again after cleaning, still there:)

Could still be that MAF, try unplugging the sensor and running with it unplugged. After a couple key cycles the PCM will ignore the MAF input and go into a "default" by reading other sensors. It will probably take a few ignition cycles to do so.

Not sure I understand your reply? What will I accomplish by unplugging it. I have unplugged it briefly and there is noticeable change in engine idle rpm and it runs rough. Thanks

When you unplug the MAF eventually it should go into speed density mode, in SDM it will use the IAT, and MAP, to calculate how much fuel is needed.
You have probably not left it unplugged long enough.

So unplugging it, the other sensors will compensate and engine will run well?

unplugging is not the proper diagnosis for this code, thats is for a no start type fault. and no it wont ever run good in open loop. back to your issue though, your code means the signal from the maf to the pcm is unexpectedly low for a certain period of time. it could be bad or the wiring for that could be bad. tough to see without a live data scanner but here is the listed diagnosis:

Causes A code P0102 may mean that one or more of the following has happened:
The MAF may be disconnected, or a wiring connection may be bad
The MAF may be dirty or otherwise contaminated (Note: if you use a reusable oiled air filter, be careful not to apply too much oil or that can contaminate the MAF).
The MAF sensor may be faulty
The vehicle computer may be faulty (very rare)
Possible Solutions The simplest thing to do is to reset the code and see if it comes back. Then start with the cheapest, easiest repair procedures: Verify that the Mass Air Flow Sensor wiring is connected properly and that there are no broken / frayed wires. Inspect for any air leaks near the MAF sensor.
Take the MAF out and clean it using a spray cleaner such as brake cleaner or electrical contact cleaner. Be gentle with the sensor.
Check the voltage of the MAF sensor (refer to a repair manual for vehicle specific information)
Replace the MAF sensor.

Thanks!!!!!!!!!!

Looking over the issue again, one thing comes to mind, vacuum leak.

Vacuum leak could set the P0102, because air is getting in, and not being measured by the MAF.
Vacuum leak could cause crappy or high idling

Vacuum leaks come in all shapes and sizes, whether it be broken/dryrotted lines, defective components, including brake booster, cruise control, HVAC diverter, a bad manifold gasket, or, and we have heard this before here oddly enough, bad injector O-rings.

I've seen quite a few people suggest replacing a MAF after getting a P0102, of course you check the wiring, and connectors first, if the voltage shows 12v, and ground to the connector is good, and there is no unmetered air entering the engine, then the MAF is most likely faulty.
He did say he has a hard/rough start condition....
And a faulty MAF can cause the P0102 code, and unmetered air (a vacuum leak) can also cause this code to show.


Here is a link to some decent info on testing his MAF.
Part 1 -GM MAF Sensor Test (P0101, P0102, P0103). BAD MAF Symptoms.

Give this a read also.
P0102 - Mass Air Flow Sensor Circuit Low
""Examples:
In many GM vehicles the code P0102 is often caused by a faulty mass air flow sensor. The repair involves clearing the code and replacing the MAF sensor if no other problems found.""

I can find more info supporting this if necessary, replacing the MAF for a P0102 if no other problems are present is not only suggested there.


So examine the MAF's thermistors, clean it with MAF Cleaner, test voltage and ground, if the problem persists then replace the MAF as it is faulty.


Justin is right about the car not running great in Speed Density mode, but if the MAF is faulty, but in most cases it should at least show some improvement in the way it runs,

Good info all I will investigate further, Thanks

update
 

Bought a good code reader and digital multimeter that reads in Hertz. No MAF codes come up but I wanted to check the action of the MAF and it seems to be working fine. I am going to blame the coe issue on my prior inexpensive code reader. It also showed no codes at the parts store. So my next step is to remove upper plenum and check fuel injection. I had a 3800 in a 88 buick I really liked, again the salt got it long before mechanical trouble.But in storage the mice or something chewed through every wire on the exposed injectors, it took some time to repair the wires but at least they were exposed:) Thanks

Have you done a resistance test, to see if each is close to one another in resistance.
https://www.gmforum.com/trouble-shoo...e-test-284313/

No I have not, thanks

You are welcome, let us know how the resistance test goes.

Also, I know how fun it is to get mice under the hood, my Park Ave has a mouse living in my air-box, and eating on top of it, tried sticky traps, and they could not hold the mouse to it, so now I am trying a quick set trap, so far I have been lucky that it has not chewed any wires up!