Diagnostic Aids

Enter this test only when all steps under QUICK TEST have been successfully completed and engine still does not start or if directed here from another test or chart. This test is only intended to diagnose:

Chassis components.
Engine vacuum.
Fuel pressure.
Fuel filter.
Fuel supply.
Fuel injector.

NOTE: During bi-fuel diagnostics, intermittent failures are possible. Perform wiggle test and tap lightly on relays during testing. Ensure LPG fuel level is correct before continuing with diagnostics.

1) Check System Integrity

Perform VISUAL CHECK under QUICK TEST. Repair as necessary. If all items check okay, go to next step.

2) Perform Road Test

Road test vehicle at highway speeds with ALT fuel switch in ALT position. If no surge is felt while driving, go to next step. If a surge is felt while driving, fuel is contaminated. Release fuel pressure. See FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CNG/LPG (BI-FUEL) article. Replace fuel system filters. Re-road test vehicle. If surge is still felt while driving, replace compuvalve.

3) Perform Cylinder Power Balance Test

Perform cylinder power balance test with ALT fuel switch in ALT position. If there is no noticeable power loss from any one cylinder, go to next step. If there is a noticeable power loss in one or more cylinders, replace intake manifold on Contour, or clear the blockage from indicated cylinder's injector sleeve on all other models.

4) Check MAP Tap Assembly

Ensure damper tube installed on vehicle is an original production part. Ensure damper tube is fully inserted, not plugged and that damper tubes are not crimped. If MAP tap assembly is okay, replace compuvalve. If MAP tap assembly is not okay, replace MAP tap assembly with a calibrated service part as necessary.