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Discussion Starter · #1 ·
about a month ago I noticed when I was driving my car was having a surge like I was feathering the gas while driving. now this being my daily driver I had to keep driving it and it ran ok for a while until the check engine light came on so I took it to auto zone to get it scanned and it gave me a p0300 code multiply misfire and a p0171 code so I started looking around on forums seeing what could me a car surge and make the idle go up and down while it park or at a stop light and what came up multiply times was tps and iac so I changed both and yet there was no change in performance of the car or the idle or the surging.so I took it to a engine diagnostic shop and for 80 bucks an hour he told me I would need a pcm reflash new mas sensor and a engine decarb well he wanted 700 for that so I figured I would shop around . well I went to autozone and bought a mas sensor to see if there would be any difference put it on and nothing no difference still stall when you raced it and idling issues still there. so I brought it back, so I was back on the computer again looking at forums and read that vacuum leaks would cause these issues got a vacuum test and there is no leaks but while I was getting the vacuum test a lot of smoke all of a sudden started pouring out of the egr but the guy said that was normal so I took his word for it, so no vac leaks . so got it home and was looking over the engine me and my dad and he noticed when I raced the engine the egr valve didn't move so we disconnected the line on the port of the intake ran a vacuum line from the egr to my mouth and when I sucked on it the valve moved and held it there for more than 30 seconds so I figured its holding vacuum so I hook the end I was sucking on onto the vacuum port on the intake so took the solenoid out of the equation and the car raced fine no stumbles or bogs just idled a lil rough. so we figured well its gotta be that solenoid so I hooked up a new one same thing egr valve still not moving when you race the engine, checked volts at the solenoid plug its got 11.91 volts with key on but I got to say when I put the solenoid on at first when I took it for a drive it was good turned it off went to go turn it on and it ran like crap the guy I bought this car off put this lt1 in this caprice it originally had the baby lt1. any help would be good I need my car its my daily driver I consider my self to be pretty good with cars but I am new to the lt1 and things being controlled by computers I am beating my head against the wall any help would be deeply appreciated
 

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I would replace the EGR and the controlling solenoid. These type EGR valves go bad after 10 years. the rubber portion gets damaged. I just replaced my EGR had backfire thru the intake. valve did not close securely all the time. the EGR can leak and the controlling solenoid gets damaged [plugged up]. the other main reason you get poor idle is PCV and all the hoses. these need be replaced if cracked or soft. PCV need be replaced @20-40K miles . more often if this vehicle is used in stop/go operation..

this is a start could be other issues ,more expensive issues.

exhaust manifold bolts broken/leaks gasket and or cracks.

the 171 is driver side O2 sensor reports a lean condition. since it is running poorly I would suspect the upstream driver side O2 sensor is correctly reporting this exhaust condition...

I along with others have just had these bolts break off. the bolts on the ends break off most often at this age.. then the issues ..
 

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Discussion Starter · #3 ·
caprice

Thanks jcat for your input I have replaced the solenoid and the egr valve was replaced about 6 months ago the egr is holding vacuum and I got volts going to the solenoid (11.90) volts but when its all hooked up and I raced the engine the egr does not move , I'm thinking about taking it back to the diagnostic place but paying that 80 an hour is hard that's why I'm trying. To see what info I can get off here I even replaced the hard vacuum lines going to the solenoid and to the egr cwm8
 

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Thanks jcat for your input I have replaced the solenoid and the egr valve was replaced about 6 months ago the egr is holding vacuum and I got volts going to the solenoid (11.90) volts but when its all hooked up and I raced the engine the egr does not move , I'm thinking about taking it back to the diagnostic place but paying that 80 an hour is hard that's why I'm trying. To see what info I can get off here I even replaced the hard vacuum lines going to the solenoid and to the egr cwm8
The EGR will NOT be commanded on by the PCM when in park/neutral/WOT/or the engine is not at normal operating temp, and Throttle position at a low amount. to check for vac operation place a T in the vac line running to the EGR with a vac gauge placed at the wiper arm see when driving how well the vac power is applying.

since the EGR is new then it may be the gasket of the EGR leaking.creating a vac leak.

what about those other parts ? bolts ?
 

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J cat you are a huge help around here lol. Im experiencing this issue too. Car idles bad when in any other gear than P or N, more noticeable when warm. I think I will go ahead and replace my egr with fbody one. I did notice a while ago that the diaphram is not moving smoothly, probably doesn't completely close sometimes.

OP have you pushed in on the diagram to try and see if spring is compressing/decompressing smoothly? I think my spring is weak and egr doesn't close all the way sometimes.

The EGR will NOT be commanded on by the PCM when in park/neutral/WOT/or the engine is not at normal operating temp, and Throttle position at a low amount. to check for vac operation place a T in the vac line running to the EGR with a vac gauge placed at the wiper arm see when driving how well the vac power is applying.

since the EGR is new then it may be the gasket of the EGR leaking.creating a vac leak.

what about those other parts ? bolts ?
 

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J cat you are a huge help around here lol. Im experiencing this issue too. Car idles bad when in any other gear than P or N, more noticeable when warm. I think I will go ahead and replace my egr with fbody one. I did notice a while ago that the diaphram is not moving smoothly, probably doesn't completely close sometimes.

OP have you pushed in on the diagram to try and see if spring is compressing/decompressing smoothly? I think my spring is weak and egr doesn't close all the way sometimes.

the EGR rubber on the old was very hard. compared to new it had to be bad . the new moved much easier...with the heat there , the spring does loose its power. only 60-70 bucks. I did notice better engine power ..my main concern was the back fire thru the intake on the cold start sometimes..
 

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Discussion Starter · #7 ·
caprice

I change my pcv valve I tried pressing the egr valve in both with the car idling and off and it oil h moved about a 1\8 of and inch but when I put a vac line straight to it and sucked on the other end the plunger moved all the way in
 

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I change my pcv valve I tried pressing the egr valve in both with the car idling and off and it oil h moved about a 1\8 of and inch but when I put a vac line straight to it and sucked on the other end the plunger moved all the way in
one of the operational tests would be to open [push] on the egr to open it at idle. the engine should idle bad or stall.

exhaust gases stop the combustion process.

if this does not happen the the intake is plugged up..carbon deposits blocking the passageways.

not on these LT1 engine but on older GM V8 carb engines I had to clear out these passageways. usually the one under the carb between the 2 primary ports.
 

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Discussion Starter · #9 ·
caprice

I went to drive the car yesterday and it felt like when j hit the gas like if j had the ebrake on it barely wanted to move when I went to the shop before the guy said he wanted to decarb the engine and reflash the computer but he wanted 700 for this
 

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I need a lil more help here guys.......could it be plugged cats???
to do a quick test/check on the exhaust being restricted you engine has 2 check valves mounted on the exhaust manifold. remove these black check valves very easy job, then see if the engine runs better. the other method if with headers no check valves would be remove the upstream O2 sensors 1 on each side .leave the holes open see if it improves.

the OEM way to check for excessive back pressure is to measure the exhaust pressure at these check valve mounting pipe threads. @ idle then @ 2000 rpm.. should be just a few PSI... hard to read though needle moves a lot..

what you need to do.. post the fuel pressure key on eng off..eng on ...key on eng off pressure holds to with in a few pri over 15 min ..

all the PCV hoses need be removed and inspected for cracks.

make sure the EGR gasket is properly installed and not leaking.

manifold bolts check all..16 bolts. esp the end bolts..near the fire wall..

you have the 171 code that should mean a lean condition.

the converters will get damaged/plugged up if you continue to operate with this condition as the PCM getting this lean condition will try to dump more fuel into the cylinders.
 

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just a thought....

Edit: my bad, didn't see all post before giving my $.02. I'll take $.01 back**

Re: the cats. They could be clogged. You can check by putting a pressure gauge on the O2 bung. Anything more than 7 psi is considered restricted flow, IIRC. Also an infrared thermometer from harbor freight($3x) will get you temps pre and post cat. Post cat should be much hotter if functioning properly. Compare both cats.
In all this, I haven't read any testing for the random misfire. See the official surge sticky for ideas. The possibilities are numerous. Do the nighttime arc inspection. Turn on car at night and in complete darknees look for arcs, keeping clear of belt and exhaust manifold of course. I've had new Delco wires arcing within the plastic shield. Just don't confuse the porcelain glow for an arc. It looks cool but an arc is distinctly different. My fix was just routing wires away from metal. Also found my new wires arcing on the morning dew alone. It would smooth out after a little while.
Lastly, check fuel trim to see which bank might be running lean. Normal fuel trim is less than 3%. Any more and the computer is trying to compensate for a vacuum leak Could be the intake gasket, mine was original at 200K and allowing air/fuel to cross chambers.
Good luck
 

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one of the operational tests would be to open [push] on the egr to open it at idle. the engine should idle bad or stall.

exhaust gases stop the combustion process.

if this does not happen the the intake is plugged up..carbon deposits blocking the passageways.

not on these LT1 engine but on older GM V8 carb engines I had to clear out these passageways. usually the one under the carb between the 2 primary ports.
Jcat, I have had to decarbon a few. You would be suprised at how many have the idle passages clogged/plugged and after cleaning the intake, the idle smooths out. If the diverter valve is leaking, this will set a P0171 for sure. Most likely cause is a loose or missing manifold bolt he hasnt found yet, or a failing injector that doesnt operate well below a certain rpm. I have had that lean code due to one injector stuck open, flooding fuel in, and that bank was being commanded lean. Oil smelled heavy of fuel.

OP , Unplug injectors one at a time at idle and plug them back in to verify its not an injector. This will set codes, but have them cleared at the store of your choosing. If you unlpug on and no rpm or tone change, thats the one your having issues with. If it only drops a little or even picks up, thats the one.


Chris
 

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Jcat, I have had to decarbon a few. You would be suprised at how many have the idle passages clogged/plugged and after cleaning the intake, the idle smooths out. If the diverter valve is leaking, this will set a P0171 for sure. Most likely cause is a loose or missing manifold bolt he hasnt found yet, or a failing injector that doesnt operate well below a certain rpm. I have had that lean code due to one injector stuck open, flooding fuel in, and that bank was being commanded lean. Oil smelled heavy of fuel.

OP , Unplug injectors one at a time at idle and plug them back in to verify its not an injector. This will set codes, but have them cleared at the store of your choosing. If you unlpug on and no rpm or tone change, thats the one your having issues with. If it only drops a little or even picks up, thats the one.


Chris
I can understand the throttle body and the intake with the carbon on a worn engine with a good amount of miles...that will effect the engines operation.

not that I am an expert on these engines injectors what about the issue with the injector coils slowly shorting out ? these I understand were not designed for ethanol fuel. then the corrosion eats at the injector coil reducing resistance, then the injector does not open enough and you get the lean code ??? 11-12 ohms is the resistance I believe.. actually the surging in the troubleshooting it is mentioned the injectors with bad connections or coils not reading the correct resistance will cause this. then there is the balance testing with the GM equipment..

I just replaced the O2 sensors on my engine . so far I can see/feel the throttle is very sensitive . same power but It appears to be reacting faster. so I guess my O2 sensors with only 70,000 on them were getting lazy ..that pass side one was a killer..

reading about the O2 with some other instruction and failure reading operation it is very much mentioned any exhaust manifold leak you can expect the O2 sensor not to properly report the correct signal. also these O2 sensors may not be fully seated this is another common issue.
 

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It basically scews the voltage offsets that are in the pcm, making it lazy to respond, if it does at all, and in extreme cases makes the it stop working all together. I have had injectors check out electrically(ohm check and audible click) and still fail to control fuel properly at lower injector opening ms times. The ethanol carries moisture and very small metallic particals with it, through the filter, and the particals attatch themselves to the coil windings in the injector, since the multec design exposes the coil windings to the fuel, and slowly over time the pintle doesnt move as commanded. I had one engine stick 2 open on the same bank effectively making them nozzles, and on another engine 1 injector on each bank had stopped working with a third being intermittant. Biggest tell was the spray pattern when they do mess up. Looks like a squirt gun not a mist like its supposed to with big drops forming at the edges of the nozzle.

I used bosch 3 design pencil style injectors on both of those cars, and have a set in my own car. Car is crisp and smooth, even with the abuse the engine was exposed to before I dropped it in so I could rebuild the original. I do recommend the voltage offset and low ms adder tables be changed for the injector swap, but it is not competely necesary.

Chris
 

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excellent info on these injectors used with this engine. so the coils are exposed to the fuel and my info says that these were designed to not have any alcohol contact.. that can explain this injector issue some have.

so if you had this injector issue with the OEM type , what is the proper injector replacement that can handle the alcohol and also be of the correct flow rate ? how much for a set of 8 ?
 

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Discussion Starter · #19 ·
caprice

PROBLEM SOLVED !!!! I took it to a shop by my house there was a short in the wiring leading to my fuel pump and my fuel pump was almost fried fix the wiring changed the fuel pump and whhhaaaallaa shes back next on the agenda is to get her to smoke the tires when it hits the passing gear like she used to
 

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PROBLEM SOLVED !!!! I took it to a shop by my house there was a short in the wiring leading to my fuel pump and my fuel pump was almost fried fix the wiring changed the fuel pump and whhhaaaallaa shes back next on the agenda is to get her to smoke the tires when it hits the passing gear like she used to
where was the short ? why did the wire short out ?
 
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