Help With A Firebird

Hello Roy,

I have a 1989 Firebird Formula, with a 350 TPI, 700R4 transmission. I have a fairly new engine (only 40,000 miles), bigger throttle body, custom-burned PROM for the ECM, headers, 50-Series Flowmaster exhaust running a duel CAT system with a single 3-inch out-pipe, and other extras.

My problem is this: The vehicle worked fine when it was finished, and I never had a problem for two years. During its first start of the day, I would hardly even hear the starter engage and it would be purring like a kitten.

Since last winter though, I noticed that it would crank a little longer before starting. Then the summer came, and it got a little better. Now that it's getting cool again the engine will die on the first start, and the second, and sometimes even the third. If I give it gas right after it starts for about three seconds it will stay running.

There are no codes present and everything is working fine. I did replace the fuel pump, fuel filter, module, pickup, coil, cap, rotor, electronic control module (ECM), ignition lock cylinder and ignition switch recently. Everything else from the plugs to hoses to the injectors was replaced along with the engine.

There is also a no-start problem that causes continuous cranking, which is why I changed the fuel pump and the ignition components. That problem has not shown its face for more than a month now so I am unsure if it is related to the cold start problem. The starting issue seems to be getting worse by the day and I am out of ideas. I would greatly appreciate your help.

Regards, Maria Davis, supervisor Fast Lane Performancenter Inc.

Dear Ms. Davis,

Well, first of all, we have to see what is missing when we have the no-start condition. Do we have a good spark? Hook up a fuel pressure gauge.

Do we have sufficient pressure when the key is first turned to on? This will help to pin down the area of concern. A defective fuel pump relay for instance will prevent the engine from starting until the oil pressure builds.

Have you checked the compression? You could have an engine mechanical malfunction when cold.

Hope this steers you in the right direction.

GMC Truck Misfire

Hello Roy,

The customer brought this GMC truck in with a complaint of a rough idle. The truck has a 4.3L, 262 CID, six-cylinder OHV gasoline engine with a distributor-breakerless ignition and a four-speed electronic automatic transmission. It has 120,000 miles.

At the first start in the morning, it didn't seem to idle that rough, but the more it ran, the rougher the idle got. The scanner showed a dead miss at idle on cylinder Number Three, but above idle, the misfire goes away.

I checked for a vacuum leak with the smoke machine and found none. Static and running compression tests both appeared OK. The exhaust gas recirculation (EGR) is not leaking and the injector waveform looks good.

I tested ignition components and replaced the plug and tried a different wire. I also checked for a partially clogged injector by adding propane, and because the idle seemed to improve slightly, I installed a new injector. But there was no improvement.

Next I looked at the camshaft position sensor (CMP) retard and found it to be retarded by nine degrees. I ground the locking tab off the distributor to make timing adjustable and reset it to zero.

After looking at some posts on iATN, I saw there were a lot of problems with lifters. One tech suggested removing the valve cover and loosening rocker arms to see if the idle smoothed out. I did this and the engine came back to a steady idle. I replaced all the lifters, put the engine back together and the same symptoms returned.

Is there something I'm missing here? What else could it be if I loosen the rockers and the engine smoothes out? Have there been a lot of valve problems on these 4.3L engines? Any help or suggestion is appreciated.

Chuck Hoffmann, Wittlin's Service Menomonee Falls, WI

Dear Mr. Hoffman:

In as much as the engine runs well with the rockers loosened, the problem would seem to indicate a mechanical malfunction. Has anyone done any head work on this engine? Are all the valve stems the same height? A valve could be seated too deeply or a valve head may have tuliped.

Are the pushrods correct for the engine? Are the valve springs in good condition? Is the oil pressure within specifications?

A careful check of these areas should produce the answer to your problem.

Faulty Alternator

Dear Roy,

The vehicle is a 2004 Ford Explorer with a 4.6L V8 engine and 4x4 automatic transmission (VIN JL6DGJ1E77K007152).

The truck had a no-charge condition, and I confirmed that the alternator was not working. I installed an aftermarket unit, and it put out 14.2 volts and 13 amps at idle. All was good, but I still had a charge light on.

I thought that I had bad unit and changed it. Same problem.

I talked with some friends, and they told me that I needed to use a factory remanufactured unit or the light will not go off. When I get a factory remanufactured alternator, the counterman tells me the same information but cannot tell me why. He says that all aftermarket remans will charge but will not turn the light off.

Can you help me understand why? Can you help a light to on in my head and off on the dash?

Mike Banovich, president USA Auto Repair, BayShore, NY

Dear Mr. Banovich

After the engine is started, voltage is applied through the warning lamp circuit from the powertrain control module (PCM) to the voltage regulator. This turns on the regulator and allows current to flow from the battery sense circuit to the field coil. This circuit also is used by the PCM to determine whether or not to send a message over the controller area network (CAN) communication link to the instrument cluster to operate the warning lamp.

If there is a malfunction in charging system operation, the regulator will ground this circuit, which sends a signal over the CAN link to the PCM to illuminate the lamp.

I would venture to guess that your rebuilder is either using the wrong regulator, or it is one of suspect manufacture that is unable to communicate with the PCM.

Jeep MAP Codes

Dear Roy,

The vehicle is a 1996 Jeep Cherokee Classic, VIN 1J4FT68S9TL290018, with a 4.0L engine and automatic transmission. This car sets a Code 108 (manifold absolute pressure (MAP) sensor voltage high) every time you start the car.

I replaced the electronic control module (ECM) twice, as well as the MAP sensor, with no results. I checked the connector at the sensor and have 5 volts there, as well as ground at the black wire.

With the connector plugged in, key-on, engine-off (KOEO), I have 4.6 volts at the signal return wire at the sensor and the ECM. With vacuum applied to the sensor, the voltage changes the same at both locations. I have also checked resistance of all three wires at both connectors. I even took the wires out of both connectors to inspect them.

I ran a new signal return wire to the map sensor to rule out electromagnetic interference (EMI), and I disconnected the throttle position sensor (TPS) and idle air control (IAC) and cleared codes, but it still reset. The only other sensor I see that shares that 5 volts is the crank sensor.

Please help before I have to set the thing ablaze and push it down a hill.

Daniel Jones, shop forman Dixie Auto, South Miami, FL

Dear Mr. Jones

You will find three wires to the MAP sensor: A 5—volt supply, ground and signal. If you are experiencing a reoccurring P0107 or P0108, unplug the MAP sensor and check for 5 volts on one lead. Hook up a scan tool with KOEO and monitor MAP voltage. Use a jumper wire to jump the sensor ground lead to the signal circuit. The scan tool should read near zero volts. If not, test your ground circuit and check the signal circuit from the MAP sensor to the PCM for a broken wire.

Plug the MAP sensor back in and recheck the 5-volt supply. If the 5 volts drops all the way to zero when the MAP sensor is plugged in, then the sensor may be shorted internally and causing the powertrain control module (PCM) to shut down the power supply. The 5 volts may not return until the key has been cycled off and on. The TPS can also short in a similar manner as the TPS and MAP shares a 5-volt supply. If either shorts internally, then they will both lose power.

The wiring from the map to the PCM runs along the firewall at the rear of the engine. Check the harness for rubbing on the fuel rail. It is not uncommon to find the wire from the map to the PCM was grounding to the fuel rail.

Remote Start Installation

Dear Roy,

The vehicle is a 2003 Ford F-150 Supercrew pickup truck, VIN 1FTRW08LX3KD22559, with a 5.4L engine and and a 4r70w transmission.

I installed a remote starter, a Compustar 2 WAM-S. All connections are soldered and sealed with shrink-tubing. The vehicle starts and runs for about 15 seconds, then shuts off. It will restart and shut off again three times, then it stops trying.

Sometimes it will start and stay running, leading me to believe it is a problem with the unit as it does work properly on occasion. I am using the alternator as a signal. In the manual it says the parking lights will flash if there is a problem, but they don't.

Have you heard of this or have any ideas?

Thank you.

Jay Campbell, technician St. George Auto, Brantford, Ontario, Canada

Dear Mr. Campbell,

The Ford Passive Anti-Theft System (PATS) uses radio frequency identification technology to prevent theft. The PATS uses a specifically encoded ignition key that contains a transponder.

The system uses the powertrain control module (PCM) to enable or disable the engine. The instrument cluster communicates with the PCM over the SPC communication network in order to enable engine operation.

The PATS system is typically not compatible with most aftermarket remote start systems. The only system authorized by Ford that I am aware of is made by Chapman. I would check with the manufacturer of the system to be sure it is compatible with the PATS system.