Question about Cars & Trucks
I have a 383 Chevy Stroker V8 engine. I have 30k miles on it (Rebuilt). I brought it to a mechanic for a basic tune up. He rebuilt my 4 barral Street avenger Holly carb, did the spark plugs, Dist cap, rotor, timed it and changed the oil. He told me that it was done and running very well. When I went to get the cart started up but the idle kept falling off. The mechanic acted c ionfused as to the cause. He eventually said that the power valve in the carb needed to be bigger to accomodate my 150 amp altinater....put it in...still an idle problem...then tested MSD ignition box, said it was faulted, was replaced but car still with an idle problem...lastly did a leak down test , showed 4 bad cylinders, cylinder 3@ 40%,cylinder 2 @30%, cylinder4 @35% and cylinder 6 @ 20%. I had no idle problem when I gave the car in, just needed a tune up...was running a little rich..thats it. Now am told I need an engine overhaul....I changed the oil every 3k mil and only used Valvoline 10w-50 oil. I only put Chevron high test fuel in the car. Finally, I took the car back...It seems to run well, the idle is a little hight 1000rpm, used to be 750 rpm. There are no visable fumes or smoke from my exhaust, The car starts well, warms up in 7 minutes, no run on when shut down. Has great power..What do you think. I told this mechanic I wanted a second opinion. Cash is tight...should I get it checked. Is it possible that I was told a lie to get expensive uneeded work done? I would appreciate any imput....I love my 81 MonteCarlo Coupe...Thanks
I suggest a second opinion would be in order as everything he did for the tune up was not altogether necessary. I consider that as the car was running ok before I would not touch the carby other than to fine tune the idle mixture to emission requirements. Any problems with the distributor cap would have showed up as a miss and the rotor button would have to be really bad but again as it was running ok. My policy is don't touch what ain't broke.Power valves in carbys are there to give extra fuel when the vacuum falls off under acceleration and do nothing else. To accommodate a bigger alternator more adjustment on the idle mixture screw would be necessary at idle but as alternator barely charge at idle the adjustment would be little. The low compressions may be from pumped up hydraulic followers and I would discuss that with the original engine builder as to what hydraulic units he fitted. but again if it was running ok before what the hell. Yes get a second opinion for sure from the engine builder.
Posted on Apr 29, 2013
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Posted on Jan 02, 2017
burned valve is likely the culprit.... or bad rings.... hook air up to that cyclinder one at a time.... and listen where the air is escaping... be aware that the motor will rotate till the piston is at the bottom of it's rotation. if it's a burned valve you will have to remove the head and replace it but somewhat easier job then replacing the rings. darn almost forgot.... it can also be a blown head gasket.... same procedure but you might need a brush and some soap water to test for an air leak at the side of the head. when you are done spray some wd 40 on it to get the water off so the spark plugs do not arc.
Posted on Sep 26, 2008
The Exhaust Gas Recirculation (EGR) valve is an important part of the exhaust circulation system of a vehicle. EGR valves have been in use in the United States since the 1960s, when car companies were seeking ways to increase the efficiency of vehicles while also decreasing pollution. When the EGR valve is clogged or malfunctioning, it can cause irregularities in engine performance such as rough idling or valve knock, indicating that the EGR valve should be inspected.
The EGR valve works by routing a small amount of exhaust back into the combustion chamber, where it can be reused. This is done for a number of reasons. The primary reason is that a certain temperature is required in the combustion chamber, and exhaust is much warmer than air taken in from the outside. As a result, the engine need not work as hard to heat the combustion chamber to optimal temperature. The second reason is that the use of an EGR valve helps to reduce nitrogen oxides, which will combine with elements in the atmosphere to form smog.
Many EGR valves are mechanical, and simply have a small valve which opens to allow exhaust into the combustion chamber and closes when it is not necessary, and to keep the air mixture optimal for combustion. Some mechanical versions will not open until there is sufficient back pressure, ensuring that the valve will not be open when the engine is idle or warming up and needs a higher concentration of oxygen for combustion. Electronic EGR valves are also available, and use electronics to regulate the valve.
If the EGR valve is stuck open, it will essentially cause a vacuum leak, leading to inefficient combustion, rough idling, hesitation, and sometimes stalling in extreme cases. This is because the car cannot combust on carbon dioxide from the tailpipe alone-it needs atmospheric oxygen as well. If the combustion chamber is flooded with exhaust from an open EGR valve, it will not function properly. To check and see if the EGR valve is stuck open, have someone idle a parked vehicle with the brake on while you examine the plunger shaft to see if it is stuck open.
If the EGR valve is stuck closed, emissions of nitrogen oxides will rise, and the car may start to knock. Spark knock happens when the fuel mixture in the combustion chamber ignites before it has been reached by the explosion in the cylinder, resulting in a disruption of the engine timing. In this instance, the engine should be warmed up and revved to see if the EGR valve will move.
In both cases, simple repairs are possible. The EGR valve can be clogged, and a simple cleaning of a mechanical EGR valve may solve the problem. In the case of an electrically controlled EGR valve or a more complex mechanical problem, replacement of the valve may be needed. The EGR valve is an expensive motor vehicle component, and care should be taken to ensure that it needs to be replaced rather than repaired. A reputable mechanic should advise you appropriately.
Failure to repair or replace the EGR valve will not lead to a life threatening condition, although it will reduce the life of your car and increase the potential emissions. Especially in areas which require smog testing, an automobile with a malfunctioning EGR valve may not pass.
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Posted on Mar 26, 2009
SOURCE: 2007 aveo misfire faults
gm has a problem with this from way back. double check your spark plugs and if they are not ac delcos, change them. ive seen this time and time again swearing, myself, that there is no way that the plugs would cause this issue. it always comes up with random misfire and usually another 1 or 2 codes misfire codes. put in ac delco, no more codes. let me know
Posted on Feb 22, 2010
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