help car boggs at low RPMs

[jhong321]

hi and thanks for the help in advance
This problem just started today. When I am just starting in first gear and starting slow about 1000-1200 rpm the car starts to bogg like it's not getting gas then up to about 2500 rpm but if i get on it it's fine it will also do this if i am crusin about 2000 rpm and just step on it a little it does it again until i step on it. I just had the car dynoed about a week ago after a tune up and it was fine 330hp rear wheels. It fills like i am not getting any gas. Have any of you had this problem? this car does have high miles( 118000) but ran fine
Thanks

 

[fhturner]

I'm no expert, so only take the following as something to investigate (or disregard):

Could it be something like clogged fuel injectors? I'm not sure why this would happen right after it had been running fine, but perhaps they need cleaning (or do you replace those at high mileage?)... When you are running partial throttle (the area where you're having trouble), you're only using the primary 8 fuel injectors. When you "get on it", the secondary throttle plate opens, as do the secondary 8 intake runners and fuel injectors. Perhaps some of the primary injectors are clogged (or not getting fuel), and when you stand on it, the secondaries make up (mostly) for the problem.

Or, could it be that you have carbon buildup on the valves and intakes? With a higher mileage engine, I would think that might be a possibility. You might try a decarbonizing additive. In other CAC forums, c4c5specialist has recommended GM's additive, part #12345515, for this purpose. Does anyone know if this is safe/effective for the LT5?

Someone with a better technical understanding of the LT5 please correct my errors!

Good luck, and let us know what you discover,
Fred

 

[Hib Halverson]

If you went from not having a problem to experiencing this "bog" on a frequent basis in a short amount of time, it's unlikely the problem is fouled injectors althought it is possible there is some other fuel system problem which is causing it.

You could tell us a little more about the problem.

I take it this occurs at light throttle and low rpm. Correct?
Does it also occur at "high part throttle", like...you don't have it floor but you're giving it more gas than you would in normal driving.
Does it occur just when the engine is warm? Just when the engine is cold or all the time.
Does the engine sputter and misfire or just has poor throttle response.

What is the condition of the ignition system?

When's the last time the fuel filter was changed?

When's the last time the oxygen sensors were changed?

Has the engine been scan tested during a road test. If so, what were the engine controls doing when the bog occured?

 

[8388]

Has the ecm thrown any codes ?

Also check the fuel pump relay. These go bad every once in a while.

 

[jhong321]

Hello All

Here is a little more info i noticed It will bog it at all temps(cold starts and hot starts and everthing in between). If the power key is OFF it will do it most of the time all though the driving range (medium to full throttle) at very light throttle you will not notice it to much. If you turn ON the power key and get on it, the bog will stop after the secondaries kick in. There are no codes. I just brought it to my friends shop today and we think it might be a bad primary fuel pump or that something is clogging it. The fuel filter was changed about 2 weeks ago along with a full tune up. including wires.

 

[Hib Halverson]

Based on that additional information, I'd agree with your friend in that the primary fuel pump might be the problem, however, I'd caution that the ZR-1 fuel sysetm is a bit complex. I strongly suggest troubleshooting the system using the fuel pressure tests listed in the factory service manual. If the primary pump in in fact the problem, the troubleshooting info will lead you there.

Lastly, if you need a pump, do not replace the entire pump/sender assy. as the manual will suggest. It's obsenely expensive.

The pumps themselves are a common item. There are some Chevy truck pumps that replace them as does the Warner P36. A pump replacement requires disassembly of the pump/pickup assy. and soldering the new pump into the harness.

 

[jhong321]

Well we took out the fuel pump and is was really dirty (original Pump) We replaced it and the problem got a little better but was still there. I think the only thing left is the injectors. i call RC enginering and they quoted me $79.99 each. I ask them if I get a bulk discount since i have to buy 16 of them the guy laughed and ask if I belong to any corvette fourms so I name a bunch of them and he then gave me a 20% discount So I ordered them I hope this will do the trick but if not I pretty sure they needed to be changed anyways. I will let you know what happens. Those guys at RC enginering are really cool people to deal with. I would highly recomend them