'86 244 bucks/surges

[Gussie]

Hello all,

About two weeks ago my previously-good-performing 300,000-mile stick-shift 244 backfired (for the first and only time) when cold. Since then has had a very nasty buck/surge beginning at very slight throttle in 1st and 2nd gears. The buck/surge is so nasty it'll chirp the tires and feels like it'll break something in the drivetrain - even though I'm barely moving the throttle from idle position.

The effect does not vary with the amount of fuel in the tank or air temperature. If I short shift into 2nd and accelerate very easily, then above about 3000 rpm it surges just slightly. In 3rd and 4th gears, power seems down slightly but the car cruises easily at 90mph. I drive the car 1000 miles a week (for two years now, most of it at 80 mph) and get about 24 mpg even with the current problem. It starts and idles perfectly. It passed smog about a year ago.

I've searched the site for tips and found a bunch. I put in new sparkplugs, wires, cap and rotor (old stuff was newish and everything looked fine); no effect. I changed the fuel filter; no effect. The in-tank pump was not working so I changed it; no effect. The main fuel pump fuse holder was cracked and corroded (and getting very hot) so I changed it; no effect. The throttle switch clicks just like the Bentley manual says it should. Main fuel pump sounds fine. When disconnected, each injector has the same effect on idle. I disconnected the AMM and then it idled very poorly.

Having ruled-out or addressed the most common problems, I'm stumped and would love your help.

Thanks

Marty

 

[olov]

i've had similar problems on my '88. but i'm hoping the guys can figure something out tomorrow when we have the meet.

good luck
i'm no help

 

[Three Fat Tigers]

Sounds like your ignition system is cutting out, might be a failing hall sensor or related harness issue.

Do you have a tachometer and if so does the needle remain steady through the bucking?

 

[jiminy14]

i dont' know much about 240's btu my 81 244 ( k-jet) backfired a couple times and the hoses going to the fast idle solenoid get blown off, along with a few otehr hoses. except the symptoms don't sound like you describe. my car jsut wont start.

probably not much help.

james

 

[Gussie]

Thanks oo4playmrright, Three Fat Tigers, and jiminy14. The problem is solved and was related to hoses...

Having read what I'd written and thinking maybe the backfire had damaged the platinum wire in the AMM, I thought I'd look at the guts of the AMM. With the car running and to remove the air box, I loosened the intake air ducts from the air box to the AMM then began to remove the bolt holding the AMM to the fender bracket. As I did that, the intake air duct from the AMM to the throttle body slipped off the AMM even though I hadn't loosened the clamp.

I removed the air box and connected the intake air duct from the AMM to the throttle body, then test drove it. Perfect! Put it all together. Still perfect!

I had tested for vacuum leaks (using ether) at idle and found none, but should have reached down there and yanked on the intake air ducts. They are so sturdy and weren't leaking at idle and I was thinking fuel pump...

I'm thinking the backfire was from a state of general mediocre tune (e.g., the bad in-tank pump), and the backfire popped-off the intake air duct from the AMM to the throttle body. I didn't find any vacuum leak because the intake air ducts are quite stiff and well-routed, so the AMM and the duct were still connected via (in essence) a semi-loose joint that leaked only a bit and/or only under load.

I'm still not clear why the effect was so strong under light throttle in 1st and 2nd gears, but it might have to do with the transition from idle settings to off-idle condition and/or (relatively) rapid acceleration under load (not possible in 3rd and 4th gears). My motor mounts are good...so it wasn't due to wildly excessive engine movement.

Good luck with your car oo4playmrright.

Marty

 

[olov]

Do you have a tachometer and if so does the needle remain steady through the bucking?

yes and yes

mine somewhat stumbles. like a skip but not on one cyl only, it's more random. when i changed my plugs about two months ago, the old ones(about 3 months old, but they were bosch +4's) the old ones were clean but real grey(signs of running hot?)

i thought it would be a dying fuel pump or clogged injector, which i could live with b/c that will be replaced for my +t soon. but if it's the something ignition, i need to figure out a fix for that

Gussie glad you found your problem

 

[olov]

Sounds like your ignition system is cutting out, might be a failing hall sensor or related harness issue.

Do you have a tachometer and if so does the needle remain steady through the bucking?

ok, so i'm ready to fix this. at the last VA meet the guys said my car sounded like a boat motor and asked what cam i have. it shakes at idle like my friends old 68 stang. and mine is a stock 88 244

so i'm hoping it's the hall sensor and not something on the harness. so my question is should i get a junkyard distributor(off an 88 244, but it looks like it was pulled out of the water so maybe it's hydrolocked or the wiring fried?) or should i try to buy just the hall sensor($69 generic one from fcp)? i really don't want to go through this agian in 6-12 months, so what's my best option?

thanks, jason