694doorbird Posted September 22, 2015 Share Posted September 22, 2015 Since I don't own any GM vehicles, im asking for some guidance. My son bought a '78 El Camino. Last weekend is really the first time I got to look at it. It has a real fast idle (just by listening to it). It will also not idle in gear until it warmed up. I did find a couple bad vacuum hoses going to the carb. Replaced those along with the fuel and air filters. That seemed to cure the idle in gear. It still sounds like it's idling fast though. Sometimes it runs on when he shuts it off. Power plant is a 305 and 2 barrel carb, auto trans. Sticker says idle speed should be 500 rpm in gear. How do I connect a tach to check and adjust the idle. I do plan on having him change plugs next time we get together. Thanks for any help. Link to comment Share on other sites More sharing options...
LFairbanks Posted September 22, 2015 Share Posted September 22, 2015 (edited) I have this tool and it can check RPM by connecting the inductive pickup on the spark plug wire. You may try one of your local parts stores to see if they rent something that may work for you. Not sure what you have available near you. Have you checked your timing and cap and rotor? Thinking about it tool stores may not rent electronic tools. Some more info that may be helpful. http://www.doityourself.com/stry/symptoms-of-a-bad-distributor-cap#b Maybe check and or replace your EGR valve too. Edited September 22, 2015 by LFairbanks Link to comment Share on other sites More sharing options...
694doorbird Posted September 22, 2015 Author Share Posted September 22, 2015 Thanks for the EGR valve replacement tip Chris, didn't even think of that one. A coworker said I can insert a wire into the positive plug on the distributor to check the rpm. Link to comment Share on other sites More sharing options...
Black Bowtie Posted September 22, 2015 Share Posted September 22, 2015 If the car has A/C it could be your fast idel switch, automatic choke sticking or timing issue. Link to comment Share on other sites More sharing options...
LFairbanks Posted September 22, 2015 Share Posted September 22, 2015 (edited) Thanks for the EGR valve replacement tip Chris, didn't even think of that one. A coworker said I can insert a wire into the positive plug on the distributor to check the rpm. Haven't heard of the insert wire trick. To me it sounds dangerous or damaging. Here is a cheaper version of the tool that I have. Not sure what your willing to spend and how often you would use it. Mine I use, and it has come in handy a number of times on various projects. Also came with a book detailing all the different functions it can check. Maybe check with one of your local parts stores. Edited September 22, 2015 by LFairbanks Link to comment Share on other sites More sharing options...
rkj4243 Posted September 22, 2015 Share Posted September 22, 2015 The wire connection for the wire is right next to the plastic wiring connector on the side of the distributor cap. You can make your own by getting a "crimp" style connector and use about a 12" long piece of wire. Not dangerous at all, just the way GM made you check engine RPM's without using some type of inductive pick-up around a spark plug wire. Also, there is an additional "idle speed screw" on the side of the carburetor which may also be what you need to look at if the vehicle doesn't have the electric operated idle speed controller which gets activated when the A/C is on. If you are going to do a tune up eventually, maybe purchase a timing light which has an inductive pick up and reads the engine RPM's? Should be able to get one of those relatively inexpensive.................................. Hope this helps you out Link to comment Share on other sites More sharing options...
694doorbird Posted September 23, 2015 Author Share Posted September 23, 2015 The wire connection for the wire is right next to the plastic wiring connector on the side of the distributor cap. You can make your own by getting a "crimp" style connector and use about a 12" long piece of wire. Not dangerous at all, just the way GM made you check engine RPM's without using some type of inductive pick-up around a spark plug wire. Also, there is an additional "idle speed screw" on the side of the carburetor which may also be what you need to look at if the vehicle doesn't have the electric operated idle speed controller which gets activated when the A/C is on. If you are going to do a tune up eventually, maybe purchase a timing light which has an inductive pick up and reads the engine RPM's? Should be able to get one of those relatively inexpensive.................................. Hope this helps you out Thanks for the info. I'm going to dig my timing light and tach/dwell meter out next time he comes over. I now have a good idea on how to read the rpm's. Truck does have A/C, so I'll look into that speed controller also. Link to comment Share on other sites More sharing options...
LFairbanks Posted September 23, 2015 Share Posted September 23, 2015 What do you connect the other end of the wire to to give you the reading? Link to comment Share on other sites More sharing options...
694doorbird Posted September 23, 2015 Author Share Posted September 23, 2015 Chris, the positive lead from the tach/dwell meter would go to the wire at the distrubitor, the negative would go to ground. When I check the Thunderbird, positive goes to the positive stud on my coil, negative goes to ground. My sons El Camino doesn't have a coil like the Ford does, which is why I was confused. Link to comment Share on other sites More sharing options...
LFairbanks Posted September 23, 2015 Share Posted September 23, 2015 Makes sense now. I was picturing, just a scrap piece of wire with no clue as to what you would get your reading from. Link to comment Share on other sites More sharing options...
Feets31 Posted September 23, 2015 Share Posted September 23, 2015 Sounds to me there are several ways this could go and maybe a $60 (price around here) scan tell you exactly what it is. Link to comment Share on other sites More sharing options...
LFairbanks Posted September 23, 2015 Share Posted September 23, 2015 Sounds to me there are several ways this could go and maybe a $60 (price around here) scan tell you exactly what it is. Cars of that age have no computer, thus nothing to scan. Link to comment Share on other sites More sharing options...
LFairbanks Posted November 29, 2015 Share Posted November 29, 2015 Mike, did you ever get this issue resolved? Link to comment Share on other sites More sharing options...
694doorbird Posted November 29, 2015 Author Share Posted November 29, 2015 Mike, did you ever get this issue resolved? For the most part we did. Turned out that the distributor has a tach connection built it. We wired up a connector to fit on the spade. Idle was set about 1,500 rpm in gear. Slowed it down to 550 or so,a and its running pretty good now. We also found a couple bad vacuum lines going to the carb and fixed those. I feel that the previous owner had the idle set so high to cover the vacuum leaks. Eventually it will need a carb rebuild, but it's not high on the priority list. (Idle rises when spraying around the carb with carb cleaner). We also changed valve cover gaskets and straightened his valve covers to fix an oil leak. He no longer needs to put a drip pan down when he comes over. LFairbanks 1 Link to comment Share on other sites More sharing options...
BrianT Posted November 29, 2015 Share Posted November 29, 2015 Carb gaskets aren't expensive, but if your gonna do a carb rebuild you might as well wait. Link to comment Share on other sites More sharing options...
LFairbanks Posted November 29, 2015 Share Posted November 29, 2015 Not sure if this is worth it to you or your son, but it is available. http://www.helminc.com/helm/Result.asp?Style=helm&Mfg=GMC&Make=CHV&Model=ELCA&Year=1978&Category=1&Keyword=&Module=&selected%5Fmedia= Factory service manual. Link to comment Share on other sites More sharing options...
694doorbird Posted November 30, 2015 Author Share Posted November 30, 2015 Carb gaskets aren't expensive, but if your gonna do a carb rebuild you might as well wait. Right now that is on his "to do list" Not sure if this is worth it to you or your son, but it is available. http://www.helminc.com/helm/Result.asp?Style=helm&Mfg=GMC&Make=CHV&Model=ELCA&Year=1978&Category=1&Keyword=&Module=&selected_media= Factory service manual. Thanks, I'll pass that along to him. I had their set for my '88 F-150, great books. I had forgotten about that company. Link to comment Share on other sites More sharing options...
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