1998 Pontiac Grand Prix 1998 Pontiac Grand Prix GTP Engine

1998 PONTIAC GRAND PRIX

180,000 MILES • 6 CYL • FWD • AUTOMATIC

LDBRUCE

MEMBER
1 POST

I have a 1998 Pontiac Grand Prix GTP (Supercharged) with 180000 miles. Recently the engine began to miss and shudder severely. Cruise control stopped working. OBD code showed cyl 5 misfire. Replaced plugs and plug wires. Ran great for 2 weeks but no cruise. Began to run rough again. Dealer said ABS module bad. Replaced entire ABS module. Cruise works, ran great for 1 month. Now runs rough again but cruise still works. OBD codes say cyl 5 misfire and crank position sensor. Replaced crank sensor and coils. Ran great again for 2 weeks now missing again. OBD code still says cyl 5 misfire. Problem is intermittent. Sometimes car runs great, other times will barely move. Problem sometimes occurs when driving down the road and entire car shakes and shudders from the engine missing. Help would be appreciated.

Nov 20, 2008 at 9:14 AM

MMPRINCE4000

✓ASE Certified Mechanic
8,548 POSTS

I would first check the fuel pressure with a mechanical gauge and replace the fuel filter if not done in the last 6 mo.
Check injectors with a noid light and inspect injector harness for frayed wires, shorts.
Inspect fuel pressure regulator for gas in vacuum line, if present, then replace FPR.

I would check compresion with a mechanical gauge, check grounds to engine, make sure they are tight.

Another possibility is the supercharger, but I would hold that as the last possibility.

Nov 20, 2008 at 9:30 AM

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