93 MTX Intermittent Kicking/Bucking

[Jrslolx]

Been chasing this issue for months and months as it comes and goes. When it acts up it is extremely violent driving down the road. Seems to be worse when its hot out and the car is at full operating temperature. Most times the car will start and drive fine when just started and driving short distances. If I drive it across town or further the issue shows back up. Check engine light comes on, only codes that show up are o2/lean codes. On occasion the car would be difficult to start after being driven and sat for a short period of time. Parts replaced listed below in order.

Fuel pump and filter-when problem first showed up about a year ago.
Both o2 sensors-about 6 months ago.
MAF-last month.
Crank sensor-This week
Cam sensor-This week
Spark plugs-This week

Only thing I can think of at this point is its some other intermittent fuel issue or its the DIS module. Crank and cam sensors were done at a buddys shop in town and have no reason to believe there was an issue with the installation. DIS modules are stupid expensive. I'm assuming they can be tested, but if its an intermittent issue what are the odds it tests bad if the car runs perfect half the time? Is there anything else that I'm missing or overlooking? I like this car most the time but is starting to drive me crazy and it's becoming a money pit with all the other little stuff I've fixed recently. Thanks in advance.

 

[Bob Gervais]

How did the plug wells look when you changed the plugs? If the plug well seals are leaking, you'll have issues eventually with the plug wires grounding out because they're soaked in oil. Also, what kind of plugs were installed? The Yamaha seems to dislike Bosch plugs. Best bet is Motorcraft or Autolite.

Speaking of plug wires, what kind of shape are those in?

When it's acting up, I'd check fuel pressure. Depending on where you got the pump, it may not be the correct pump for the car. I forget who has improper listings, but I do know that there are a couple of chain parts stores that do. Even if the pump is correct, getting a fuel pressure baseline when the car is acting up will help diagnose the issue.

The DIS modules aren't really something that intermittently fail. They're either good, or bad. That said, with your issue being present only when the weather is warmer, it is possible that there's a short/broken circuit in the DIS that only shows up when it's warm. Tough to test them for this, I'll agree, but perhaps swap in a known good used one, along with the proper heatsink paste, and see what happens?

 

[Jrslolx]

Autolite plugs, wires look good, spark plug wells looked clean. Pump was a Walbro 155. Don't recall the part number. Problem with troubleshooting it when it acts up is as soon as you shut the car off the problem may not come back when you start it or even for a few days.

 

[Bob Gervais]

Issues like that are tough. Doesn't sound like it's fuel pump related, though I've heard of a few cases of the Walbro 155 pump going bad. In fact, mine crapped out earlier this year, after about 10k miles.

Maybe installing a fuel pressure tester, and duct taping the gauge to the windshield? I've done that before with good results.

 

[Jrslolx]

That wouldn't be too tough, the fuel pump was replaced chasing this same issue though.

 

[auto.guru]

ive had people tell me that a "brand new reman starter is good for the rest of its life"

and let me tell you....

i took that reman starter right off the shelf from advanced and took it to auto zone, tested it, and it failed.

Bob has a good point

 

[projectSHO89]

Your symptoms are consistent with an intermittent cam sensor problem.

When I got my last 94 ATX, it was doing the same thing. Finally found that somewhere in its previous life, the cam sensor had been replaced but there were now TWO rubber gaskets inside the connector instead of one causing it to seat intermittently. Removed the extra gasket and the thing never acted up again while I had it, over 60K miles.

 

[ShadetreeSHOguy]

Yep, same issue i had with my 94 mtx. would buck, throw a code, then drive fine. Ended up the cam sensor was being ruined by the cam seal leaking onto it.