Need Help with Stumbling Problem
Thread Starter
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
Need Help with Stumbling Problem
I've been chasing a problem for way too long. My car was running great and then suddenly developed a miss or stumble. The problem is at all speeds but runs especially bad under load. I have checked ignition with a spark tester and verified good spark to all plugs. So I believe it is a fuel problem.
I checked fuel pressure. Fuel pressure is good at idle but drops to 0 quickly when engine is off (within less than a minute). I have an adjustable fuel pressure reg, so I replaced the diaphram. No change. I replaced the injectors. No change. The fuel pump is nearly new but is next on my list. I used the procedure of clamping off fuel lines to find where the pressure is going. It drops with both supply and return lines pinched off. That tells me it's a leaking injector, but the injectors were replaced. I'm baffled.
I checked fuel pressure. Fuel pressure is good at idle but drops to 0 quickly when engine is off (within less than a minute). I have an adjustable fuel pressure reg, so I replaced the diaphram. No change. I replaced the injectors. No change. The fuel pump is nearly new but is next on my list. I used the procedure of clamping off fuel lines to find where the pressure is going. It drops with both supply and return lines pinched off. That tells me it's a leaking injector, but the injectors were replaced. I'm baffled.
Melting Slicks
Joined: May 2010
Posts: 2,082
Likes: 3
From: Conowingo Maryland
know you said you used a spark tester to check for spark but I would put the car on a scope to get a good look at what is happening. If you cannot do that or do not want to do that then you need to elemiate 1 thing at a time. When was the last time the car had a good tune.(plugs cap rotor wires ect.). You could be expericing something very minor to a more serious problem(burnt valve, Cam, ect) A scope is your best friend to narrow down a miss unless you want to go threw a lot of testing and time. Here is a one way to try to narrow it down to the cyl that is giving you trouble. Get engine to operating temp. idleing unplug one injector at a time. each one should change the way the engine is running. When you get to the one that does not change the engine that should be the cyl that is causing the miss. This is assuming that we are talking about a miss.(one of more cyl. not opperating right)
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