Tech Tips

FORD ESCORT/ MERCURY TRACER-1.9L. ENG- 1991 & LATER- NO START AFTER BROKEN ACCESSORY BELT

If you get one of these vehicles that experiences a no start or a lack of power condition after someone replaced a broken accessory belt, check to see if the crankshaft trigger wheel is out of sync. When a belt breaks, sometimes it finds its way between the crank sensor and the trigger wheel. As a result, the trigger wheel, which is pressed onto the crankshaft damper, will rotate on the damper, just enough to create a no start or a lack of power condition due to retarded base ignition timing. A quick way of verifying this is to bring the #2 cylinder to top dead center of the compression stroke. Now, check to see if the crankshaft position sensor is lined up with the missing tooth space of the trigger wheel (refer to diagram). If it is not, then you have found your problem. At this point do not attempt to repair the damper. It must be replaced.

James D ‘Anna — Top Gun Technician

GM CARS W/ 3.4L ENG.-HARD START, BACKFIRES WHILE CRANKING, STALLS

This tip applies to the 3.4L “S”, and “X” engines with a manual transmission. Specifically: 1993-91 Lumina, Grand Prix, and Cutlass Supreme with the 3.4L dual overhead cam engine; and 93 and up-Camaro, Firebird with the 3.4L OHV engine. These vehicles may be hard to start, backfire through the intake on cranking, or may stall upon deceleration or at any low speed when the clutch pedal is depressed.

Both of these engines use an inductive or permanent magnet type crankshaft position sensor. With this type of sensor, the distance the sensor is situated from the triggering wheel or crankshaft will influence sensor output. What we have seen in some cases is that the crankshaft thrust bearing is worn enough so as to position the trigger wheel on the crankshaft far away enough to limit the crank sensor’s output, creating the symptoms we have described. The correct specification for crankshaft end play for both engines is .0024″ to .0083″. By the time the vehicle is in your shop exhibiting these symptoms, the end play is usually much greater than the specs will allow. The fix is to check the crank thrust surfaces, and if you’re lucky, only the thrust bearing will have to be replaced.

Peter Mc Ardle — Domestic Specialist

GM “G” SERIES VANS- 1986-92 – ELECTRICAL PROBLEMS

If you do any type of electrical trouble shooting on these vans, we have experienced that the bulkhead connector on the firewall of these vehicles has been more than a major contributor to the electrical problems that these vans experience. It seems that this connector is not immune to corrosion problems from the elements. Compound that with the fact that the battery is not too far away. Any type of overcharging problems as well as a leaking battery will add some sulfuric acid to that connector, resulting in more corrosion. We have seen many cases of: no start, hard start, intermittent trouble codes, inoperative speedometer, inoperative gauges, intermittent light operation, and false ABS codes just to name a few!

Julio Oyola — Domestic Specialist

BUDGET DIAGNOSTICS

Most of us may remember that we have an old carburetor fuel pressure gauge sitting someplace in our tool box. You remember? Only reading up to 15 psi and also measuring vacuum? This tool can be an invaluable aid in helping diagnose problems even with the newer fuel systems that we see today. One use can help if you think you may have an intake air leak in a V type engine, and the intake valley is sealed to the crankcase and the heads. Please, DO NOT add propane into the crankcase. This method has been known to cause explosions within the crankcase from unexpected combustion, sending valve covers into orbit. Instead, disable any crankcase breathing or ventilation systems, then block all of the breather ports leading to the crankcase. Next, install your vacuum/pressure gauge onto the oil dipstick tube.

After starting the engine, observe the gauge. Your gauge should never indicate that vacuum is present. If your gauge does, then you have found your intake leak, which is in the valley area. Even a tight engine has some blowby, and since you have closed the crankcase, the gas has nowhere to go. This creates some pressure that should be indicated by your gauge. Another use for your old gauge is to check fuel system operation. Many vehicles use dual fuel pump systems. Others use three pumps as well as more than one fuel tank. Most of the dual pump systems use a lift or supply pump in the fuel tank together with an external high-pressure pump. When the pressure at the fuel rail is low, here is a way to determine which pump is not working properly. Using a “T” fitting, install your gauge between the high and low pressure pumps. With the pumps running, check your pressure reading. If the low-pressure pump is OK, you will read low pressure. If the low-pressure pump is not working correctly, or, if the fuel inlet is restricted, you will read vacuum on your gauge. This is the result of the high pressure pump doing all of the work.

Jeff Auerbach — Domestic Specialist