This picture is typical of terminal identification of the tpi harness from 1985-1989, with maf. When you are probing wires, with the harness plugged into ecm, be careful in identifying the terminals, so you get the proper diagnosis.

This picture shows the terminal identification for the ecm #1227730.

If you have a harness and ecm#1227727 from a Corvette, this is the terminal id's. These are also identified as (A) Yellow or "Y". (B) Red or "R". (C) Green or "G". (D) Black or blue or "B".

No Start or extended start, fuel system problems: If the electrical system checks out, and you are still having problems getting the vehicle started, we'll look at the fuel system. Low pressure and no cold start enrichment are two common problems we'll look at.

NOTE: A no start condition can also be a possibility of a ecm that you are using has VATS programmed in the prom. The majority of 1988 and later ecm's (#1227165, 1227730 and 1227727) have vats programmed in the memcal. There are two ways around this, (1) Have the VATS  taken out of prom or (2) have a prom decoder module installed.

WARNING: Gasoline is extremely flammable. Observe all safety precautions and work in a well ventilated area, turn off pilot light, extinguish all flames, and do not smoke in presence of gasoline vapors and liquid. TPI fuel pressures can be dangerous if mishandled and will cause personal injury or death.

This is where you will need a fuel pressure gauge. The most common problems of fuel pressure is a ruptured fuel regulator diaphragm, fuel pump check valve not holding, loose or leaking connections, leaking injectors. Locate the fuel gauge connection valve on the rear right side of fuel rail near regulator. Wrap a shop rag around the connector, while installing the pressure gauge, to absorb any leakage. When you turn the ignition key on, and the system pressures up, see that you have 40-47 psi in the system. You may have to cycle the key more than once to obtain maximum pressure. A slight drop of a couple of pounds over a minute is considered normal. Start the engine and note pressure, it will be 3-10 lbs. lower with engine running. If it is not, you'll have to use your hand vacuum pump and attach it to the fuel pressure regulator vacuum line. Apply around 10" of vacuum, the pressure should drop by 3-10 lbs. If it does not, you'll have to replace the regulator diaphragm. 

Now, if you are having a low pressure problem, check for restricted fuel lines, or clogged filter. If you are using a old tank from a tpi car and it has been sitting around, it may have enough sentiment to clog the filters, the fuel  pump "sock" and the in line filter. If the pressure checks out at this point, block or pinch off the fuel return line, and apply 12V to the fuel pump test connector and note pressure. If it goes above 45 psi, replace fuel regulator. If it below 40 psi, check for a faulty in tank pump coupling hose, pulsator, wrong inlet filter, or even wrong fuel pump. 

An excess pressure problem can be checked this way: disconnect the fuel return line at the pressure regulator side and install a 5/16" flex line, insert other end in a gas can, and look at the pressure within 2 seconds of fuel pump prime. If the pressure is between 40-47 psi, correct restricted fuel line to tank. If the pressure is still high (above 47 psi) check for restricted line from pressure regulator to point line was disconnected. If the line checks our, replace the regulator.

If all this checks out, you'll have to suspect leaking injectors. Pull your sparkplugs and check for saturated or fouled plugs. If the bad injector can not be determined by this method, unfortunately, you'll have to pull the plenum to access the fuel rail. With this in mind, once you have disassembled the plenum where you can unbolt the fuel rail, leave the fuel lines hooked up. Raise the fuel rail up enough so you can see the tips of the injectors. Wipe the injector tips dry with a clean paper towel. Prime the fuel pump for several seconds to obtain a high pressure and observe the injector nozzles, any dew like drops or wetness indicates a bad injector. You'll have a choice in either trying to use a injector cleaner yourself, have it professionally cleaned or replace the offending injector. Most times a leaking injector is caused by extremely small particle lodged in the needle, just as much as a dirt particle in a needle and seat of a carburetor, and you know the havoc that causes! Sometimes, especially if you are using old injectors from a donor car, they may be just plain worn out!, keep this in mind when you are doing a swap project.

If you have tpi system that uses cold start injection, this injector can cause a pressure drop in the system. With a cold engine, coolant temperature below 95 F, the cold start circuit should activate. If you suspect this injector may be leaking, first thing is to disconnect the distributor 4 way connector to keep the injectors from being activated during cranking the engine. Pull the connector on the cold start injector, and prime the fuel pump for several seconds, and note the fuel pressure. If the pressure drops, pull the cold start injector and see if there is any wetness on the tip. if there is you can have this injector cleaned or replaced. Most of the time, if your cold start injector is leaking, you can just about bet the fuel injectors are too.

Excessive crank time, extended start time:  

 If the fuel pump system electrically and mechanically checks out okay. If the vehicle starts readily in warm weather, but progressively gets harder to start as weather turns colder, the cold start injector is most likely at fault. The system is basically simple electrically. The power is provided through the purple wire from the ignition switch, through the cold start injector, to the tan wire, and is grounded through the contact in the cold start switch. You can pull the cold start injector and check for it being clogged. Pull the injector and hook up your injector tester and hook each end, one to ground and touch the other end to 12V hot. You should hear a distinct "click", telling you the injector is activating. Try blowing through the inlet side of injector with it electrically activated, if you can at least blow through it (there may be quite an effort to do it, but if you can get air through, the injector is good). Just remember the pressure your using is significantly less than the 40-47 psi of the fuel pump!

Pull the connector off the cold start switch and check with ohmmeter. If the resistance between the terminals on the switch is above 200 ohms, replace it. If the resistance is between 20-200 ohms, be sure the coolant temperature is below  95F, replace the switch.

If the cold start switch and injector check out, check the circuit. Unplug the distributor 4 way connector. If you have a remote start button, hook it up, with the red lead to the battery, and the black lead to the starter solenoid (purple wire).  Otherwise, you'll need a assistant to help you. With your test light hook to ground, probe the purple wire on the injector terminal with your test light, crank the engine just for a second or two, just enough to see if the test light comes on. If it does not, check to see if the crank fuse is blown. repair the circuit if you have a blown fuse, before proceeding any further. The circuit is protected by a 10 amp fuse, don't think you can get by by putting a higher rated fuse in the circuit, or you'll risk damage to the electrically system! If at this point, if the light does come on, connect the injector back up, and pull the connector from the cold start switch. With the test light hooked to ground, probe the terminal's tan wire, with the engine cranking for a second or two. If the light comes on, the circuit through injector and harness at this point is okay. If not find and repair this connection.  Probe the purple wire with the engine cranking. If the light comes on, the circuit that provides power to the cold start switch heating element is okay. If not find and repair the circuit.

The cold start switch has two circuits in it, connected to a common ground. When the switch is energized, the heating element will limit the cold start switch on time to maximum of  8 seconds. This is because the heating element heats up the thermoswitch circuit, opening it up when the temperature reaches a specific point around 95 degrees F. The bimetal switch is also activated by coolant temperature. When it is below 95 F, the thermoswitch is closed, above it is opened. It also must be noted that the colder the coolant is, the longer time the cold start injection stays activated, as the coolant temperature goes up, the activation time is shorten proportionally. 

Extended crank time, speed density: 

 Common causes are a faulty CST, MAT, and MAP sensor. Also a faulty egr valve and clogged or leaky injectors can cause the problem. Since the speed density has the enrichment programmed in the memcal based on temperature and manifold vacuum, checked these items first. Check the circuits and sensors for tight connections and no open or grounded wires. Usually if you have a sensor fault it should set a trouble code. Repair these items first. A malfunctioning egr valve will set a code if the egr temp switch detects the valve is not opening once the operating parameters are met. Check the operation of the egr solenoid and the condition of the vacuum lines. A faulty map sensor that detects a load on the engine when if fact there's not can set a code or at the very least skew the injector calibration. The fuel system checks use for a maf system is also valid for checking speed density.                                                                                                                  

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