Piston Slap: Throwing (Ignition) Parts at a (Fuel) Problem?

Sajeev Mehta
by Sajeev Mehta
piston slap throwing ignition parts at a fuel problem

Chris writes:

Hey Sajeev,

Long time lurker here. Since you asked so nice, here’s a problem that I haven’t managed to troubleshoot myself, and so far my own searches & forum postings haven’t nailed an answer. My girlfriend drives a 99 Mazda Protégé. If driven for an extremely short distance (like from the street into the garage), it will not start the next morning. It turns over just fine, but doesn’t catch.

I’ve found that I can eventually get it to start by holding the gas pedal to the floor & cranking, followed by easing up on the pedal slightly (maybe 1/2 or 3/4 of the way down) & continuing to crank. This process takes 5 – 10 minutes, so there’s lots of breaks in there as well.

Almost everything on the spark side has been replaced for different reasons (I was chasing engine codes the wrong way). So I’m pretty sure it’s not battery, spark plug/wire, or coil pack related. Simiarly, I’ve changed the MAF, O2 sensors, cat, & the acordian hose that feeds from the intake to the throttle body (the hose being what was actually causing the codes, BTW). None of these changes seemed to affect this particular problem.

This lead me to believe the problem must be fuel delivery in some way, but now I’m second guessing myself. The problem seems to happen most often when it’s cold & damp outside (by Georgia standards).

Normally I’d have changed the fuel filter by now, but it’s not a separate unit. It’s attached to the pump & sits in the tank. That’s probably going to be my next step. Before I do that I wanted to run this by you. Any ideas? Someone suggested the the charcoal canister could be trapping water vapor (since the engine is never hot), and then forcing that vapor into engine when I try to start it the next morning. I’ve never played with that before, but if that’s right then shouldn’t there be a hose I could disconnect & see if the car starts?

Anyway, if you have any suggestions, I’d love to hear them. This isn’t an urgent problem, but it’s one I’d like to be able to solve.



PS, here’s another write up of the problem, just in case I missed something. Mine’s the 3rd post.

Sajeev answers:

Thanks for your letter. I like the post on the Mazda Forum, especially since you did my homework for me. And by your own admission, you threw parts at a problem instead of finding the proper diagnostic for the engine codes generated. Are the codes still present?

Your problem sounds like a lack of fuel, and I seriously doubt that’s a stretch for me to armchair analyze that from my remote vantage point. Check the fuel pressure with the key on, engine off. Compare the reading on the gauge to what your EFI system needs to run properly. If you are at the lower end of acceptable (or worse) you have found your problem.

Maybe a bottle of fuel system cleaner in the tank is all you need. Or maybe a fuel filter. Or maybe the fuel pump itself. Or maybe the fuel injector’s resistance is out of spec. Or maybe the fuel pressure regulator, or its associated vacuum plumbing. My point is, this is hard to guess from my laptop.

My advice is to start with a fuel pressure tester and buy a filter, maybe a pump after that. Also make sure the vacuum lines to the regulator aren’t fossilized, gooey or cracked. If they aren’t as soft/pliable as the rubber on your shoes, replace them.

Good luck on your hunt, I am sure your girlfriend appreciates your hard work…provided you never, ever throw parts at a problem again. Never again, son!

Send your queries to sajeev@thetruthaboutcars.com . Spare no details and ask for a speedy resolution if you’re in a hurry.

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2 of 22 comments
  • Moparman426W Moparman426W on Mar 15, 2012

    It's most likely the fuel pump or the pressure regulator. The fuel pressure should have been checked before throwing all of those new parts on it.

  • 406driver 406driver on Mar 15, 2012

    My car has done this a couple of times and I think the problem is caused by petrol flooding. There were no ill effects afterwards so the comments about faulty parts didn't apply in my case. The best cure is, as someone has already said above, to avoid driving it a very short distance.

  • Analoggrotto Knew about it all along but only now did the risk analysis tilt against leaving it there.
  • Mike Beranek Funny story about the '80 T-bird. My old man's Dart Sport had given up the ghost so he was car-shopping. He & I dropped my mom at a store and then went to the Ford dealer, where we test-drove the new T-Bird (with digital dash!)So we pull up to the store to pick mom up. She walks out and dad says "We just bought it.". Mom stares at the Mulroney- almost 13 grand- and just about fell over.Dad had not in fact bought the T-Bird, instead he got a Cordoba for only 9 grand.
  • EngineerfromBaja_1990 I'd love a well preserved Mark VII LSC with the HO 5.0 for a weekend cruiser. Its design aged better than both the VI and VIII. Although I'd gladly take the latter as well (quad cam V8 and wrap around interior FTW)
  • Teddyc73 The Mark VIII was the first car I lusted over as a young new auto enthusiast. Still think it's a beauty after all these years.
  • Art Vandelay wish They’d do an SS version of the Bolt. We need more electric hot hatches and this is a clean enough design that it would look good