Contour Enthusiasts Group Archives Forums General Troubleshooting Could this be a fuel pump?

Just started this a couple of days ago:

low rpm (<3000) heavy throttle the car bucks and misses bad enough to trip a misfire flashing CEL.

high rpm (>5000) car is just weak and accelerates (if at all) like a yugo missing on two cylinders. Doesn't shut down, but it won't pick up at all.

at mid rpm's steady state driving it runs perfectly smooth

problem gets worse as car warms up

with the key on but engine off I hit 38 PSI fuel pressure - so my question is: Is it possible to get these symptoms if a pump is flow restricted even if it can hit normal pressure with the engine off?

(Plugs and wires are brand new, coil is 2-3 months old, I threw in an EGR block plate (made from a Mt. Dew can last night to rule out a stuck valve, and swapped in my spare MAF sensor this afternoon to rule that out too.)

With a flashing cel you are in 'limp home' mode...I'd get the codes pulled first...

Thanks Terry!

to add info to my earlier post:

It was acting up for about 2 days before the misfire tripped.

I had my OBD scanner on it capturing data when she went. I went out to intentionally push it hard because I knew it was running poor, and wanted to try and get a clear signal of what was wrong. Unfortunately the only thing that I saw was what my butt was already telling me - it was running really rough and had failed the continuos monito "EGR Open" test. That led me to block the EGR, which did not help.

Today on lunch I checked fuel pressure, swapped in my spare MAF sensor and dumped the PCM, which still did not help.

If I pull the fuel line at the return side of the rail and run the "all outputs on" test, I'll get a full 8 seconds of fuel pump on time. I don't recall for sure, but if our pumps run at like 40G/hr that would be about 10-12 oz's pumped. I guess that would be a quick check to definetively rule out the pump right?

Even more info:

At WOT bank 2 O2 never got above .48V, while bank1 seems to hit about .89V. Definite fuel problem, but not sure if it's pump or injectors/wiring???

Since bank 2 is closer to the fuel supply inlet I'm thinking injectors are more likely than fuel supply. Could be a bad wire as when I switched to the 19# mustang injectors last Christmas I did have to do a little "twisting" to get the connectors on - but I wouldn't think a pulled wire would take 9 months to show up?????

But wait, I noticed under light throttle cruising both bank 1 and 2 O2 reads look identical and perfectly under control which I wouldn't expect if an injector were dead or shorted?

I had almost the same thing in my car. It felt like it was missing at low RPM, and weak up top. I went through a ton of stuff, you know what it was... I replaced my wires, and it all went away.... hope this helps

I know it sounds basic, but make sure your plugs are OK. I've had similar issues when I had a plug back out. HTH

I would suspect plugs and wires first, since you did just replace them. Probably something in there is bad.

Thanks for the replies re plugs and wires, I'm pretty sure there not the culprit - but it's worth checking again (~24 dollars for plugs vs 180 for a new pump! Wires were FMS 9mm). "Brand new" meant they were put in about 2 - 3 weeks ago, and have been running fine untill now.

Also, it seems very unlikely a misfiring plug could force an entire bank of cylinders to lean out at WOT - I'd think you'd end up slightly rich from the unspent fuel and get some backfires from it hitting the cats.

The chart of O2 is just plain ugly! Not only couldn't it hit the rich WOT state of about .89 - .90 volts, there are spots where it was truly lean (lean of stoich) at about .4 - .45, and only averaged about .5V This was continuous over the 5-6 seconds it took to trip the misfire code. After going back to normal cruising the engine smoothed right out and the O2 reads started to oscillate normally.

Just an update to those searching the problems forums wondering if they have the same problem:

Q: did the fuel pump fix the problem?

A:
Subject: Re: fuel pump

Yes - mostly. What pushed me to do the pump was the complete loss of acclereration and misfiring at WOT, and the new pump and fuel filter completely cured that. Also bumped my around town MPG from 19.ish to 20.ish.

I still have a bit of a flutter once in a while, and maybe once every couple of weeks it feels like my secondariues totally stop opening, so I think the secondary controller may be getting weak. I've been meaning to tie open my butterflies again to see if it totally resolves the problem, but I've been too lazy.

Welcome back Terry!