5.7l Fuel Pressure Regulator

jseabolt · July 27, 2011

OK. Dad's 1998 1500 Express, 5.7 liter 120K miles. The van idles rough, exhaust does not smoke but smells rich and gas mileage has dropped in half. It shows three codes. Random missfire (twice) and O2 sensor bank one.

The guy at Advance Auto said it's not the O2 sensor but the fuel pressure regulator is faulty.

I'm mechanically inclined but often refer to shop manuals for help.

I'm looking at the Hayne's manual and I'm confused about where the regulator is. Is it on the fuel rail or is it underneath the upper intake manifold. The black and white photos are very confusing because I cannot see most of the engine (because it's a van).

From what I gather it appears the procedure is to relieve the fuel pressure, remove the engine cover from inside the cabin, cup holder first to access the rear of the engine. Pull the breather and intake hose. Disconnect the throttle and cruise cables, PVC hose, disconect the fuel lines. Anything else in the way that might prevent the upper manifold cover from being lifted off the engine.

Then the regualtor should be mounted on the distribution block where all the injector hoses lead from. Or is it on the fuel rail?

ChevyTech77 · July 27, 2011

Its not the fuel pressure regulator. They don't fail on these. Probably a junk injector poppet if its fuel related.

jseabolt · July 27, 2011

Its not the fuel pressure regulator. They don't fail on these. Probably a junk injector poppet if its fuel related.

Really? That makes me feel even worse.

I've decided to just take it to a certified GM mechanic. This looks like an all day job in order to pull the upper intake manifold and I hate to waste my time replacing this part if that's not the problem. I don't have the special GM tools to test the fuel pressure and such and think this job maybe better for someone else to tackle.

Once the van is repaired I'll post a follow up on what was wrong with it.

ChevyTech77 · July 27, 2011

Could be something simple but pulling that upper intake, honestly, is pretty easy. Either way, if you don't feel confident, sometimes its best to just take it to somebody who is. No shame in that.

jseabolt · August 19, 2011

Could be something simple but pulling that upper intake, honestly, is pretty easy. Either way, if you don't feel confident, sometimes its best to just take it to somebody who is. No shame in that.

Sorry for the late update. It was the distributor cap and/or rotor button causing the misfires on 3 and 7 cylinders. Had nothing to do with the fuel injection system.

First of all, I've never seen a bad distributor cap cause 2 cylinders to missfire. On the other hand I've never let a distributor cap get to the point to where it caused an ignition problem. I'd just go ahead and replace it every 60K miles or so. Also I thought by 1998, just about all cars had coil packs instead of distributors. My 96 Explorer had a coil pack.

Unlike my '03 Subaru which developed a misfire, my code reader told me which cylinder it was. A loose connection at the #3 plug crapped out the plug wire in about 2K miles. With this van the code just said "Random missfire". If the code reader had pointed out two cylinders were missfiring I would have went straight to the ignition system. Judging from the smell of fuel being dumped out the exhaust, I could have sworn the fuel injection system was flooding out.

I'm assuming the shop I took the van to which are run by two exciled Buick mechanics when the dealership changed hands, have a better machine than I have.

ChevyTech77 · August 20, 2011

Yeah, on that old of a vehicle, a general code reader won't show you which cylinder is misfiring. You have to have a scan tool that can read the pcm's data list to see which cylinders are misfiring.

The caps, on those distributors, were actually known for issues as well.