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Discussion Starter · #1 ·
Hey all, this is on my 95 RMS that I picked up. The problem is when you give it gas anything over just like revving and let's say you stab it pretty hard it bogs and backfires through the intake. The car didn't run when I got it so the things that I changed are as follows

-ICM and coil, one of them was bad, just put a good assembly on it.

-Fuel pump, guy I bought it from put the wrong one in it and it wasn't mating to the output tube, fuel pressure with key on is about 44 psi, idling it is about 38, when you rev it it will jump back up towards 44 then dip back down, don't think that it is an issue, just wanted to note it.

-EGR was seized, took it off last night and cleaned it out, don't really see any movement when applying a vacuum to it, could this be the issue? Not sure on if the EGR system would cause this, the FSM states that it isn't operating when in park or neutral.

Just curious if anyone else has had these problems and what was the fix.

Thanks in advance.
 

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My money is on the ignition system, plugs, wires, and optispark, especially if its unknown when they were all last changed. I remember a similiar thing happening on the first Caprice I bought about 11 years ago(95 Caprice w/ 80K miles or so) that on take off had some hesitation. Did the optispark, plugs and wires and the problem was solved, forget if I did the coil on it though.

The EGR issue if it is seized closed wouldn't cause an issue because no exhaust gases are passing through it. The EGR valve is opened up at cruising speeds to help lean the system a bit and to burn off a bit of a little bit of the exhaust gasses and to help lower the combustion temperature. If it is stuck open it could definitely cause issues, but it would be an issue with rough idle and stumbling or even stalling if severe enough. I would replace it with the F-body EGR valve.

Somewhat related to that is check the exhaust manifolds for broken bolts(especially on the drivers side rear 2 bolts) and cracks (especially on the passenger side between cylinders 6 and 8) can also cause similar issues, but most often causes exhaust leaks and tapping noises. My landlord is working on a 2000 Ford Explorer right now that one of the catalytic converters cracked at the O2 sensor fitting causing massive idle issues. Hope this information points you in the right direction. - Peter
 

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Discussion Starter · #3 ·
Hey Peter that is a good call, I can see the wires are new, but you are right who knows, the kid also told me it only sat for 2 months, when it in reality sat for a year and a half and you can tell by the weather checked tires on it. I have to change the opti anyway it was removed when I got the car and he had broken the vent line nipple off the bottom of it. No exhaust leaks just went through and installed pretty much all new components. So I know that is good. Thanks for the advice I appreciate it.
 

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Discussion Starter · #4 ·
Well changed the opti and it is still the same problem, stab the gas and it hesitates and more often than not it will backfire through the intake. Now with that being said I have an issue that no one can tell me what it is, when the fuel pump primes or even if you jumper to the lead in the engine bay so it continually runs, it sounds like the fuel rail is burbling, but the fuel pressure will hold up to FSM spec, I would think that it is a stuck injector but I am not sure at this point, I may have to shoot a video of what I am talking about, I am going to load the tune that I tweaked for it tonight sometime and see if something happened when I turned the VATS off and deleted the air pump on the tune that I loaded into the car. Not sure what is going on, oh and one other thing that is pretty boggling, if the car is warm it won't do it, riddle me that one :)
 

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i got the same exact issue!!! im going to change out the opti.. i will be pissed if it still goes on.
it only happens every now and then ...when idle u can hit the throttle and nothing will happen no backfire or when starting the car does it TURN and when u let go it acts like it wants to start and u get the great smell of rich fuel?
 

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Not sure what is going on, oh and one other thing that is pretty boggling, if the car is warm it won't do it, riddle me that one :)
Not to question your ability as you have helped me on more than one occasion. Do you think the ECT or ETC or whatever that sensor in the WP is called may be the problem? I think that sensor feeds info to your pcm for fuel and timing based on coolant temp.

Just a thought...........
 

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Discussion Starter · #8 ·
what happens if u slowly increase throttle?

Ah I should of mentioned that, it is fine if it is slowly increased past a certain point and you can rev it all day long.

Not to question your ability as you have helped me on more than one occasion. Do you think the ECT or ETC or whatever that sensor in the WP is called may be the problem? I think that sensor feeds info to your pcm for fuel and timing based on coolant temp.

Just a thought...........
Nah that is cool man I am human and I forget sh%% that is for sure, but that is what I thought of originally and I checked it with my computer and it is rising like it should, so I don't think that would be the problem but I am going to run a scan of it tonight later and see what data master file looks like and see if I see anything out of the ordinary.
 

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Discussion Starter · #9 ·
i got the same exact issue!!! im going to change out the opti.. i will be pissed if it still goes on.
it only happens every now and then ...when idle u can hit the throttle and nothing will happen no backfire or when starting the car does it TURN and when u let go it acts like it wants to start and u get the great smell of rich fuel?
Mine does it after start it and cold it bogs then revs, and like I said most times it will back fire through the intake as well, but not all the time, but as I stated above in regards to what Wolf stated, if you slowly rev it is fine, no issues, and of course when it is warm it doesn't miss a beat. So with that being said I would bet that it is an Open Loop condition but I am not entirely sure at this point, it almost seems like the engine has to be warm and not relative to open or closed loop either,, but I will check on this later and see if it stops when it goes to closed loop, I am going to read up some more on the differentiation between the two to make sure that I am thinking correctly. Also the Fuel noise has got me boggled I will have to film a video so everyone knows what I am talking about. Maybe the Fuel pressure regulator but I would think that I would see it bleed down, well it does but it takes forever, after I shut the car off, it maintains 40 psi and drops to maybe 30 or so after about 2 hours, I would think that it within spec, but there is no reference in the FSM really for this. I should probably take out the IAC and clean that as well, it maybe sticking when it is cold and once the engine warms up it loosens itself up.
 

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Mine does it after start it and cold it bogs then revs, and like I said most times it will back fire through the intake as well, but not all the time, but as I stated above in regards to what Wolf stated, if you slowly rev it is fine, no issues, and of course when it is warm it doesn't miss a beat. So with that being said I would bet that it is an Open Loop condition but I am not entirely sure at this point, it almost seems like the engine has to be warm and not relative to open or closed loop either,, but I will check on this later and see if it stops when it goes to closed loop, I am going to read up some more on the differentiation between the two to make sure that I am thinking correctly. Also the Fuel noise has got me boggled I will have to film a video so everyone knows what I am talking about. Maybe the Fuel pressure regulator but I would think that I would see it bleed down, well it does but it takes forever, after I shut the car off, it maintains 40 psi and drops to maybe 30 or so after about 2 hours, I would think that it within spec, but there is no reference in the FSM really for this. I should probably take out the IAC and clean that as well, it maybe sticking when it is cold and once the engine warms up it loosens itself up.

well i guess u gotta love them Lt1's ! when i changed my TCS and the car is warmed it it will start up in 1 turn with a knock though ? idk what thats about.. but im just riding along im going to do the same ill let u know if if i find anything or if it makes any diffrence... Will wait for the Vid and i got my $$$ that the sound is the Same im dealing with..i figured it WAS or can still be Fuel issue
 

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not egr.......

what pops in my mind is, cam position sensor, vaccum or optical sesnor..


idk something is might be up with the fuel system....does it have hard starts?
 

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Discussion Starter · #12 ·
Not really hard starts couple cranks and it fires, this would indicate that the fuel system is in fact bleeding down, but it has a new pump in it and fuel pressure is great, so I would think that would be it, could be vacuum I could try the propane test tonight when I am out dinking around with it.

Could be optical sensor and I am not sure where the cam position sensor is, I know 96's have crank position sensors, so I am not sure, as far as the optical sensor, it is a totally different opti, I wanted to try it to make sure that it wasn't the opti or if it was before I dropped the money for one right now and it does exactly the same thing, I will check the opti harness connection up top as I know at the unit it is good and see if there is an issue with it. Could be the IAT sensor or wiring for that as well, since the PCM mainly looks at this sensor when cold from what I am reading in an open loop environment. Not sure I am going to dink with it tonight once the wife goes to work and the kiddo is in bed. I will let you know.
 

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I would try a MotorVac before throwing any more parts at it..
 

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Discussion Starter · #15 ·
Motorvac is a good idea, I will have to find a place in town to do it for me and not rip me off,

as far as plugs they look good, but I will double check them tonight, I may take off the fuel rail set it above the injector holes and fire up the pump and see if there is an injector leaking, maybe or maybe not, I will see what I come up with, thanks for all the advice.
 

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I have the same issue. Only I've compounded it by having a throughly messed up tune.

When the engine is cold it will stumble and nearly die if I stab too much (sometimes as little as 25%) throttle too quickly. Like trying to pull into the gas station across traffic. As soon as it warms up to closed loop the problem goes away. I've also noticed it is worse when the ambiant temperature is colder.

I'm interested to see what you get figured out.

Anthony at PCMPerformance suggested checking my spark tables. However mine are all stock unless changing tire size and the VE fueling tables make a difference.

I'm pretty new to tuning and it seemed to me that running with the MAF unplugged and dialing in fuel trims first seemed the way to go.

- Brian
 

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Discussion Starter · #17 · (Edited)
Thanks for the insight Brian, I went out a f'd with it for a bit this evening, ran a couple of datamaster scans with it, well one before I tuned it and one after. I still think that I may have a stuck injector or something, I am uploading the video of the noise in the fuel rail now to youtube, it sounds like fuel is rushing through it, I do remember that I checked all of the ohm values of the injectors and they all matched up but one and it was lower, which would make me believe that it could be a possible sticking injector. Fuel pressure was kindof all over the place, hooked up the gauge went to 44 immediately, unhooked the prime line to the fuel pump it drops to 38, FSM stated 3-10 psi it should fall after key off, so it is right in the middle. so I said screw ran the car to see if the trouble is still there let it warm up and run for a bit while logging the run, did the same stumble and backfire, dependant on how hard I pressed the gas. So after that I pulled the tune that I had on it which is pretty much factory except for VATS and AIR delete and loaded in the one that I had been working on. The the fuel pressure only dropped to 40, WTF. anyway car was warm about 170 degrees F, with the new tune, it fired immediately no cranking, no knock counts, when originally with the factory tune it was up about 2700 or so. Rev it and it revs fine, but it seems like 180 degrees is the sweet spot number, not sure, I am going to let it cool for a bit and go out and fire it up again with the new tune when it is cool and see what it does. I am betting that it is still there. Oh another thing to note I found a broken vacuum line a plastic one that I think is for the HVAC it runs in with the harness on the back of the motor down to the firewall it looks to me. Here is the video of the fuel rail noise I am going to look at the datamaster files.
 

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I've never heard a noise like that. I think you should pull the fuel rail and turn on the key, see if any injectors are stuck open. Could be a bad fuel pressure regulator, as well.

You mentioned finding a vacuum leak. Fix that, it isn't helping.
 

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Discussion Starter · #20 ·
Thanks man, yeah I plugged the port where the vacuum leak was at, I think that it has to do with HVAC, so I would suspect there is no leaks now, didn't do a propane test but maybe later, you are right on pulling the fuel rail, I definitely planned on doing that, I am guessing that once this injector is warmed up, that is if it is sticking, that it unsticks itself, at least that is what I am hoping, I am going to go fill the gas tank and put some injector cleaner in it and run around for a bit and see what happens, I think that is the key that I need to get some gas through it, it sat for a long while despite what the kid I bought it from told me:) Not that the injector cleaner is going to help a ton, but it may.
 
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