Engine stumbles on acceleration

[Tobben]

The above title seem to describe my problem well. During hard acceleration it may loose traction. So it doesn't lack power. But during normal acceleration it stumbles. It doesn't run perfect at idle neither. Anyone has experience with this? I have installed new plugs, plug wires is ok, new distributor cap and rotor, new air filter, checked injector ohm's ok, new coil wire. The left rear o2 sensor wire is cut of. I'm not sure this sensor will make my engine stumble, as it's not a primary O2 sensor. A GM mechanic was scanning my vette couple of weeks ago, it didn't have any troublecodes and he said the o2 sensor was working. The instrument information is out, so i cant read codes from it. But yesterday i was reading emission values from a emissioncontroll tester, and the CO was 2% Lamda between 1-0.9 and HC 13. The O2 went below 0.6% during 3000rpm.
Any advise or information would be most appreciated
Been working so long on this corvette now and there is so much to do:eyerole

 

[c4c5specialist]

HI there,
Take a look at your coil wire and the ignition system.
Allthebest, c4c5

 

[jmccloud]

Engine stumble

Yes, the rear O2 sensors do not control the engine; they evaluate the functionality of the cats.
Certainly the coil, wires and control module (near the coil) can cause stumble but usually cause worse stumble under hard acceleration.
Three items that might cause poor idle and moderate acceleration stumble are the IAC=idle air control, TPS=throttle position sensor and the EGR=exhaust gas recirculator. There are many threads you may search on each of these but basically the posts suggest cleaning the IAC and make sure it travels easily, measuring the closed/open voltage values of the TPS (I can't recall the values but guess 0.5 closed, 5v open - these may be backwards), and assuring that the EGR travels open/closed as vacuum is applied, that the EGR closes fully with no vacuum and that the EGR valuum control solenoid functions correctly (a tough thing to do). Of these potential causes, I've had experience with EGR's failing to close due to carbon flakes and broken return springs in the actuator. The symptoms were much like your Corvettes; idle and mid-power roughness but excellent full power performance.
Hope this helps and let us know when you find the solution.

 

[Paul Higg]

I had this same problem, you might consider overhauling your throttle body.

Paul

 

[Tobben]

I havent checked any of the mention below, so i will look into them tomorrow before job. Thanks for the advice, most appreciated
The idle is high, just above 1000rpm and the engine seems worse when its hot. I'll give the solution once i found out what's wrong .

 

[jmccloud]

High, rough idle speed

The PCV=Positive Crankcase Ventilation valve can also cause your symptoms. Test by disconnecting it from the rocker cover (PCV remains connected to intake plenum) then hold your finger against it to stop air flow. If your idle steadies out (becomes uniform) and drops several 100 rpm, the PCV is bad. Some suggest shaking the PCV valve and if it rattles, it's OK. Not a reliable test.
Good luck.

 

[Tobben]

I'll give it a try thanks

 

[Tobben]

Guess i figure my main problem. Water in the fuel tank. On new years eve, i empty my fuel tank, finding a layer of water at the bottom in the tank. Clean the tank and empty the rest of the fuel system. Today, before job. I filled the tank with fresh fuel and injector cleaner. Fired it up. Made it idle inside the garage until it got hot. The idle was near perfect, smooth and quite. Hitting the accelerater, just a small hint of stumble, on low rpm. Perhaps my injectors isn't as good as it should be. Got an advice from a fellow work mate, clean them in Aceton. I will do that tomorrow i guess, if it doesn't get any better before. Anyway, this is going the right way
Thank's for all of the replies

 

[jmccloud]

Injector cleaning

I definitely would not use acetone to clean the injectors.

If you had residual water in the fuel, some methyl alcohol will 'grab' it and carry it through the system and slowly clean out the water. Changing the fuel filter will speed the clean up (even if the filter is new, a small amount of water will 'blind' or plug up the filter somewhat).

If you have only a small stumble and the injectors' resistance is correct, running the engine at length with 'dry gas' (dilute methanol) is the safest cure. Repeated or concentrated use of the methanol will eventually degrade fuel lines, o-rings, etc. but not nearly as fast as acetone.

Good luck

 

[gmjunkie]

I definitely would not use acetone to clean the injectors.

 

[Tobben]

IMG_0820.jpg - Image - Photobucket - Video and Image Hosting
IMG_0819.jpg - Image - Photobucket - Video and Image Hosting
I didn't read your reply before i cleaned the injectors with Aceton. Saturday morning i went to work. Were the Vette is stored. I removed the fuel rail assembly, then the injectors from the assembly. And then the O-rings from the injectors. It's quick and easy thing to do. I poured some Aceton into a plastic cup, but the bottom melted right away. I used a metal cup instead. I placed one injector into the cup. Then i mounted two wires into the injector stick. I used a 9V batteri, were i held the Positive wire on the batteri and tapped the Negative. The injector open and closed for each time. I did this for a minute and a half for each injector. I saw vibration in the cup for each tab, and when i was done the injectors were shining inside and outside
I installed the fuel rail assembly and fired her up. The vette was running ok. But not propely on all of the cylinders. I used a emission controll tester, and the HC was too high. So now it has fuel delivery, but there may be lack of spark. My time went out. So i havent done much since. Tomorrow i'll try figure out why.

 

[Tobben]

I ohmed my injectors again, they were 12.3 OHM. My workmates said it shouldn't mean much as long as the mechanical bit works. Is this true? There are sparks on all of the sparpluggs, there are compression on all of the cylinders and i just cleaned the injectors and managed to open and close them with 9v battery. When the engine was running, not on all of the cylinders, i took off one injector stick at a time too see if the engine was running rougher. I took off the stick to injector number 2 and 4 and 6 and still no respond on the engine :confused even with all three of them off.
It responded when i took off the stick to injector number 8,1,3,5,7 - one at a time. It doesn't sound like it's running on just 5 cylinders and there were no change in HC (unburned fuel) on the emission tester when the three stick's were off. Leaking injectors? Anyone with experience with this? I appreciate any of your reply on this subject

 

[gmjunkie]

Have you ran a compression test??Is the engine loosing coolant??

My thinking is you may have a seeping head gasket or some lobes removeing there self from the cam,weak or broken valve springs,burnt valves!!You really need to run a compression test and see what you have!!

 

[Tobben]

Thanks for the advice
But i have already run a compression test and it was ok. I have also used a emission control tester above the coolant tank, and there were no exhaust in the coolant. So the head gasket's should be ok. I havent found any water in the oil yet neither. I'm going to check the signal to the injector once i have time with an oscilliscoop- to check if the Powertrainmodul is working. If it is then i guess i'll just order new injectors and pluggwire's.

 

[John Robinson]

Vacuum

You don't say if you also have problems with the cruise or climate
control heating cooling system in car.

You might try to see if the vacuum lines going into the vacuum switch under the right hand fuel rail cover are broken. You also need to check to see if the vacuum switch is bad. If any of that is bad then the vacuum is not up to par and could be causing the problems you describe.

You might also check all the electrical plugs for corrosion on the pins.



This can also be a source of your symptoms

 

[Tobben]

I havent checked the vacuum switch, but i have used a spray can with ''engine starter'' around the intake and vacuum lines. The engine didn't react, so there aren't any vacuum leaks.
Yesterday i switched the heaterpanel off. That usualy stops the fan in the engineroom when it's cold. But the fan was actually off all the time after that. The engine became very Hot at the end. I checked the airscrews for air in the coolant system but there were none. It was missing a bit coolant though. I filled it up. I started the eninge again, the fan wasn't working, so i pushed a button on the heaterpanel and turned the heat up in the coupe. The first fan stared right up, and the second soon after. The engine temperatur fell down to around 190*F. This can't be right, so there is probably a problem with the climate system or something too ;squint:
I havent used the cruise yet.

 

[JAKE]

From memory, in stock configuation, with everything working correctly, the first fan won't turn on until the coolant temp is well above 200F. However, when you turn on the A/C, the fans come on immediately.

Ballpark, the first can turns on around 220F and the second fan around 240F when the A/C compressor isn't being used.

Any climate control setting that calls for the use of the A/C compressor turns on the fan.

Since the engine has a high idle that won't drop, I suspect the following:

Engine has a vacuum leak;

Defective Mass Air Flow Sensor

Throttle body butterflies sticking slightly open,

IAC not freely moving,

Throttle position sensor defective

It would be helpful to know if your engine is able to go into Closed Loop.

By the way, I would definitely repair the wiring to the rear 02 sensor. Feedback from that sensor may be cause of or contributing to your problem. In tracking down the cause of a problem it's essential for ALL the sensors to being working properly, if for nothing more than to eliminate them as a possible cause.

Just my thoughts.

Jake

 

[John Robinson]

I havent checked the vacuum switch, but i have used a spray can with ''engine starter'' around the intake and vacuum lines. The engine didn't react, so there aren't any vacuum leaks.
Yesterday i switched the heaterpanel off. That usualy stops the fan in the engineroom when it's cold. But the fan was actually off all the time after that. The engine became very Hot at the end. I checked the airscrews for air in the coolant system but there were none. It was missing a bit coolant though. I filled it up. I started the eninge again, the fan wasn't working, so i pushed a button on the heaterpanel and turned the heat up in the coupe. The first fan stared right up, and the second soon after. The engine temperatur fell down to around 190*F. This can't be right, so there is probably a problem with the climate system or something too ;squint:
I havent used the cruise yet.

This switch may not leak vacuum at the hose connections but think of it as a gate valve or diverter internally. If it does not hold vacuum at the right time it would be the same as having a vacuum leak internally.

Take the valve off and hold your fingers over the small connectors and suck on the large end. Try several different methods that is one small connector at a time and then both. If you are not able to hold vacuum inside the check valve it is bad.

 

[Tobben]

The front O2 sensor left and right and right rear are the same. But the rear left is is to small to be a O2 sensor and doesn't look like the rest. That's the one that's broken. Don't know what it's purpose is yet.
The idle went down after i cleaned the fuel tank from water. But it still doesn't run on all of the cylinder's. It has copression and spark. I gave it thought and i've just ordered injector's from South Bay Injector's. If that doesn't help, then at least i have new injector's that i know that work's
Chunck's from the inside of the catalyst has started to appear behind the muffler's. All of the unburned fuel is tearing on the catalyst, and if i don't fix the my problem soon, then i'll probably need new catalyst as wellhnoes
Anyway, thanks for your advice, most appreciated . Being a Mechanic for just 5 year's i really haven't that much experience with Engine Management System :eyerole.