The other modules all require an ECM to function correctly. If the battery is fine, make sure the wire feeding the distributor is sufficient. If you have a computer controlled distributor in your car right now you can’t do much to increase performance other than to make sure it is correctly communicating with your car’s ECM and upgrade the coil to a better unit. You can temporarily add a heavier spring just for the initial timing adjustment if you cannot lower the idle enough. dual coil units. Find part numbers from the Wells parts catalog PDF above. The nylon distributor shim kits are sold through Summit and Jegs, etc. The Chevrolet small-block engine is a series of V8 automobile engines used in normal production by the Chevrolet division of General Motors between 1954 and 2003, using the same basic engine block.Referred to as a "small-block" for its comparative size relative to the physically much larger Chevrolet big-block engines, The small block family spanned from 262 cu in (4.3 L) to 400 cu in … Holley’s Terminator Stealth EFI systems have the same great … The stock HEI uses a vacuum advance canister to further tailor the ignition timing. Having excessive vacuum advance can cause detonation at throttle tip-in and can cause surging at light throttle cruise when the vacuum advance is fully deployed. By adding the second coil they now had one for each bank of the engine which was an ingenious and effective solution. If there is no EGR being used, the amount of vacuum advance needed will be around 10-12 degrees. Steel cams require a bronze or plastic composite gear. I drive a ’78 Oldsmobile Delta 88 Royale. If this is the case, the engine will idle high when out of gear and then the idle speed will drop down once it's put in gear, and the off-idle response will be poor. Note: Portions of this page appears to have been cut/pasted from a thread located at 72chevytrucks.com. In many cases that means there can be as much as 50 degrees of advance when the engine is cruising under a light load. What has to be avoided is too much timing under load; too much timing under load can cause engine-damaging detonation. If so, you probably remember that distributor issues were usually fixed with a fingernail file and a matchbook. On the SBC there were three different combinations of damper lines and timing tabs that go together. Plug it back in when the timing has been set. In the case of the SBC, #5 and #7 are next to each other on the cap, at the head and in the firing order. Next measure the secondary side of the coil: Test carbon pickup between carbon end and spring end - resistance will be 4000- 6000 ohms. Stock advance cans may provide as much as 22°-24° of advance. This low voltage could be insufficient to get the distributor to fire. Note: In almost every case, using the advance kit-supplied weights and cam will not work as well as using the stock weights and cam along with the different springs. All carbureted GM engines in cars built from 1980 to about 1974-'75 and trucks from 1986-back use this type HEI distributor. If this is encountered, a simple momentary off switch can be wired into the wire that supplies battery current/voltage to the HEI. The springs are located directly under the rotor and are easy to remove/replace by hand or with needle-nose pliers or hemostats. Failure to do this can lead to an early failure of the module. Find part numbers from the Wells parts catalog PDF above. By using ported vacuum and an adjustable vacuum advance can, you can give the engine extra timing under light throttle cruise conditions. Note: Other carbs have similar transition circuits, and they need to have the throttle blades in the 'sweet spot' same as a Holley. You will need to know which one of these you have stock to order up the appropriate aftermarket coil. The amount of mechanical advance that is supplied depends on the mechanical advance cam and weights that operates the centrifugal advance as well as the limiter slots in the weight plate and the pins in the plate that holds the rotor. Another neat wiring aid is the Accel p/n 170072. In addition to the interrupter switch, a starter brace should be used to help prevent broken starter noses or damage to the mounting ear of the block. There is no more need to worry! So don't be surprised or alarmed if you end up with a curve that is different from what is presented in this article. The "missing" 6 degrees can come from the vacuum advance. You want to end up with ~0.020" (no less than 0.015") on a Chevy distributor; some engines like the Olds need to have the end play adjusted differently. It is all but impossible to give exact timing numbers because of the variations in engine builds and conditions in which these engines run. There's a fairly wide tolerance, but it should not be infinite and it should not vary as the wires are flexed and moved around to simulate it in use. But do not use paper distributor gaskets stacked together as shims. A relay that delays the ignition from being energized- giving the starter time to get the engine turning over- can be wired into the ignition feed wire. That would be fried from a solar flare or EMP, but pop a new one in, and I’ll be back on the road in 10 minutes. Take the measurements with feeler gauges. The all in by rpm is often said to ideally about 3000 rpm, or less if the engine will allow that w/o detonation. Don't try to use a computer controlled HEI unless there is an ECM. Wider plug gaps (or faulty ignition wires) cause voltage spikes in order for a spark to occur. The correct gap is 0.035"- 0.040" for the majority of cases. Once the engine is turning over, the switch is released. The other end of the brace attaches directly to a threaded boss on the engine block, just below where the block deck and head meet. Remember, any change to the initial will also require the mechanical advance to be changed a like amount so as to keep the total advance where it needs to be. Note: See the articles on rebuilding the HEI below. After determining how much mechanical advance your HEI is giving you, and it's determined it's too much for the amount of initial advance you want to run, the mods to the mechanical advance are shown in the image below (thanks to 69-CHVL of Team Chevelle). You will need to remove it and take it to an auto parts store that has a module tester. The NON-computer controlled HEI can be made into a great distributor for a street or street/strip car. This will help keep the carb primary blades from being opened too far to get the idle speed where it needs to be. The primary resistance value should be between 0.6 – 1.5 ohms. The module also controls how much "dwell" the coil receives between firings. That also means that a fingernail file is no longer the repair tool for roadside fixes. If the meter jumps around as the wires are flexed, or if the resistance is drastically higher or lower than 600Ω-1000Ω (or is infinite), or if there is a reading between either wire and the metal case of the pick-up coil, it's bad. Swap springs until you get it close to these specs. The max mechanical at 3000 rpm is 18 degrees. One thing to watch out for by using more vacuum advance is the engine can 'surge' at elevated advance settings and also there's the chance it will have a transient ping when hitting the throttle quickly when the vacuum advance is all in. And your plugs can develop carbon deposits within just a few thousand miles. The vacuum advance will compensate for the engine load. On the coil-in-cap GM HEI, the coil is located on top of the distributor between the plug wire towers under a plastic cover. The small spring on the button goes against the bottom of the coil. They also have positive retention clips that prevent the connection from falling off. Many times, a low-voltage issue can cause a myriad of problems. These relays may be found from any number of suppliers, one is Wolsten Tech out of New Jersey. A distributor is an enclosed rotating shaft used in spark-ignition internal combustion engines that have mechanically timed ignition.The distributor's main function is to route secondary, or high voltage, current from the ignition coil to the spark plugs in the correct firing order, and for the correct amount of time.Except in magneto systems and many modern computer controlled … Holley has you covered with the new Terminator Stealth Throttle Body Fuel injection System. To make sure it is not the hot wire, run a temporary jumper wire directly from the positive side of the battery to the distributor. You can run without a vacuum advance but expect your highway mileage to suffer, possibly more. Often a stock distributor is set up to rely on the vacuum advance for a large proportion of ignition advance. A bad distributor can wreak havoc on your engine. You can upgrade the coil with an aftermarket replacement that can produce more volts and total spark energy. This isn't what's wanted for a performance timing advance curve. The HEI centrifugal advance is susceptible to wear. P0351: Ignition Coil A Primary circuit fault. Generally no more than 10°-12° of vacuum advance is needed with a performance ignition advance curve. Initial advance recommendations, from: Demon carbs. As has been already stated, most performance engines will work well with around 10-12 degrees of vacuum advance. A lively discussion on ported vs. manifold vacuum is HERE. To test the pick-up coil assembly and its wires, use an ohm meter and measure the resistance between the two wires at the terminal (unplug the pickup from the module). If the voltage drops below 10.5, check your battery. A gasket can be used under the shims. You will want to note that there's not enough vacuum at WOT to cause the vacuum advance to work. Chevy Hardcore NEWSLETTER - SIGN UP FREE! If not it's bad. Using a manifold vacuum source will in many cases- depending on the cam and compression- allow you to close your throttle plates a little and still maintain the same idle speed. It will have no ill effects at WOT because there will be no vacuum at WOT (no vacuum = no vacuum advance added to the timing) so you will be running exclusively on mechanical advance. Note: Pay attention to the idle speed while setting the initial timing! On low budget builds, a replacement coil and module may give adequate performance, depending on the application. A performance cam having excessive duration/overlap/tight LSA specs could require more initial and less mechanical advance. Many times, a low-voltage issue can cause a myriad of problems. Great article! ACDelco D-1906/GM p/n 10482820 (used in the GM ZZ4 crate engine). To test the resistance of the coil, remove the coil cover so you can see the red and yellow wire. Also, the centrifugal advance plate (that rotates on the main distributor shaft as the centrifugal advance moves it), near the top of the distributor shaft sometimes gets gummed up and "sticky," slowing the advance curve and generally preventing the centrifugal advance assembly from working correctly. But it will cause the ECM to throw a code (the check engine light will be illuminated) because the ECM senses if the computer-controlled portion of the distributor is functioning every time you start the engine. It is usually recommended to use a vacuum advance, and that the vacuum source be manifold vacuum. The HEI ground is through the distributor body to the engine, then to the battery negative cable. Testing the secondary circuit of the coil. The HEI distributor has eliminated the need to do roadside tune ups to a point-style distributor. If the resistance tests verify the coil is fine, you’ll need to test the magnetic pick up coil next. On a Chevy V8, the vacuum advance can should be pointing roughly at the passenger side front tire. Vintage Chevrolet Commercial: What Makes The Monte Carlo So Great? Many performance curves call for around 10°-12° of vacuum advance on top of the 32-40 degrees of total advance (initial plus mechanical), to give somewhere in the neighborhood of 50 degrees of advance under light throttle cruise conditions. There have been reports of various quirks associated with some aftermarket modules, so research them beforehand. Depending on the application this could mean rewiring or replacing the resistor wire for a 12-14 gauge supply wire. This page has been accessed 536,110 times. It is always preferred to work up to the optimum timing a step at a time. P0736: Improper Ratio for Reverse Gear. For a daily driven street car, using a vacuum advance is always recommended. However, the scope of this article at this juncture doesn't include a full run-down of modified computer-controlled or aftermarket HEI distributors, but is instead primarily aimed at reworking a stock-type HEI for performance duty. The remaining electronic part that would keep the distributor from firing is the module. How many of you reading this remember a time when distributor diagnosis meant checking the points? from Moroso, Mr. Gasket, Jegs brand, and others as well. Mechanical advance all in by =/< 3000 RPM. © 2020 Power Automedia. Each engine is different and what works for one engine might be a little different than what works for another engine. So always start adjusting initial timing without the mechanical advance adding any timing. They also knew that by adding larger coils, there performance was enhanced accordingly. They will soak with oil and compress more than when dry. Crane vacuum advance limiter plate pn 99619-1. If that occurs, the secondary throttle blades may need to be opened slightly to allow more idle air to be introduced into the engine. This powers up the ignition and the engine will start without kickback. New replacement HEI power and tach hook-up pigtails are available. The 2 wire plug from the coil to the distributor module is used to power up the distributor and provide a coil trigger for spark. Click toolbar for various cam duration specs. The more radical the camshaft, the higher the initial advance for a given compression ratio. Stock, it's capable of about 35,000 volts and so-so total spark energy. This is located inside the distributor, and has the green and white wires from the pick up attached on one end, and a terminal block on the other. There are 2 different designs of the HEI coil. So fix it first or get another HEI to start improvements on; just make sure you are getting the right one for your engine- they were used on ALL makes of GM inline and V6/V8 engines and all look similar. It will also deter engine run-on, or "dieseling". We will safeguard your e-mail and only send content you request. The module is the electronic controller that takes the place of breaker points. It should read between 6000Ω and 30,000Ω. Wells catalog to be used for looking up representative part numbers to find specs for testing. Installation is a simple one-wire hookup. But once the RPM goes up and the cylinder pressure increases, the chance of a misfire increases dramatically with a wider plug gap. Comes with instructions and an allen wrench to adjust it. Ignition Coil Primary circuit fault. What is needed are the right springs, the right initial advance setting and the right amount of mechanical advance (vacuum advance will be discussed later). Stock, it's capable of about 35,000 volts and so-so total spark energy. Using a relatively mild camshaft and compression ratio matching the cam, if using an EGR valve, more vacuum advance may be needed to compensate for the diluted air/fuel mixture it causes- much the same condition that a cam having a lot of overlap can cause. © 2017 Power Automedia. It’s a combination HEI battery/tach pigtail that has a connector for both power to the HEI and the connection for the tach, molded together. Also, you may find that the engine is cooler running around town in traffic and has much better throttle response. The only other change you can make in the advance curve is to manually advance the base timing (usually worth a little HP by itself). Many parts stores can test the HEI ignition module at no charge. Make sure your 12-volt wire is connected to the spade connector labeled BAT. The drawing below shows the transition slot as seen with the carb held upside down. With more RPM, more advance is needed, up to a point. Aluminum is cheaper- but in this case you really do get what you pay for. You may well end up using more initial advance than the figures stated. Non-computer controlled HEI setup for performance. In the case of an OD vehicle where the cruise rpm is relatively low, you can supplement the advance curve by allowing the vacuum advance to give more advance than what's usually recommended. 1981-86 trucks/vans with 305s (RPO LB9) used a variation of the computer controlled HEI with electronic spark control with 5 pin modules. Build your own custom newsletter with the content you love from Chevy Hardcore, directly to your inbox, absolutely FREE! To run the engine efficiently without the ECM, sensors, and related equipment fully functional, the distributor and carb need to be replaced at the least. What vehicles came stock with a non-computer controlled HEI? To do this, you will need a 1/4-inch nut driver and a multi-meter. If the connections are good, you next need to make sure the unit is getting a strong 12 volts. This wire should be part of your original wiring or can be purchased separately. Stock, the HEI distributor advance mechanism is pretty good but the stock springs are too strong, causing the advance curve to come in too slowly, if it ever gets fully advanced at all. This allows the distributor to sit lower in the engine. The increase in advance for a lightly loaded engine will increase fuel economy, lessen emissions, and can give smoother engine operation. You may find as much as 16 degrees of vacuum advance is needed with a relatively mild cam if an EGR system is used. The correct gear material/treatment has to match the type of camshaft being used. Another thing that is often overlooked, is if the cruise rpm is less than the rpm where the mechanical advance is all in by, the vacuum advance has to make up the difference to get the best mileage and drivability. If an attempt to change the advance curve is made on a distributor that suffers from these problems, the mechanical advance may not work as smoothly as needed.
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