part throttle drivability problems / rough idle / no accel unless floored

[gears351]

HELP!!

1989 SMEC (Shelgame cal) 2.5 T2 in a Dakota

been running fine, had some really cold weather sweep in (first time with this motor at 0 F / -15 with windchill) and all of a sudden it's running horrible. Part throttle (1/4 to 3/4) stumbles, falls on face, will not accel. Floor it and boost goes to 12 and I can pull away from a light.

I had a code 12, 11, and 13 so I pulled the MAP off, swapped it for the old one (replaced it chasing issues when #4 piston was cracked) so the code 13 went away and I got a code 14. Double checked all connections for corrosion and tightness, code 14 went away but still runs like crap. Cam timing is spot on.... Dizzy cap looks good (thought the center contact on the cap might be toast) plugs are NGK Iridiums and they look clean but the gap looks crooked (Still at .035 though). EGT is right at 12-1400 off #3 and everything else is running like always.

Anyone got any ideas?

[RoadWarrior222]

Sounds like a closed loop problem, so far. It'll be in the sensors or wiring to them... maybe more specific thoughts later, trying to brain it through.

---------- Post added at 06:13 PM ---------- Previous post was at 06:10 PM ----------

Oh, disconnect the coolant temp sensor, and see if it's "easier" to drive round, though it will still probably have poor throttle response... Pulling the CTS should put it into open loop.... whereas as soon as the O2 is warm and unless you're at WOT by the TPS, it's trying to be in closed loop.

[gears351]

you know, that could be - it runs decent cold but as soon as it's up to temp it runs like crap. Think that's the CTS? what kills me is checking the plug I broke the stupid retainer clip off.....

I'm still thinking it's the tps or the map but I'm not getting any codes besides the 12 since I reset it.

[trannybuster]

Had a 02 sensor do this, I unplugged it and it ran fine.

[gears351]

You left it unplugged?

[turbovanman²]

Code 13 is a vacuum problem to the MAP or bad MAP, so make sure the line is getting full manifold vacuum, code 14 is a MAP wiring issue or bad computer.

Code 12 is normal, code 11 could be a bad HEP. Also check the baro solenoid, could be going bad, bypass it for shitts and giggles.

[gears351]

bypassed bario - straight vac (hard) line to map. HEP caused a no-start after I pulled the cap to check the contacts - cleaned corrosion on hep plugs and it fired right up.

Reading the other thread on part throttle drivablitiy I saw someone mentioned the alternator caused running issues at speed - I've got a new alt but my voltage runs high at times (above 16).

I hope it's not the SMEC it's a boostbutton unit and I've not had any problems since we got the right cal in it.

[turbovanman²]

It could be the actual SMEC and not Rob's cal. I had issues with one computer, drove me nuts, tried everything, finally changed out the computer, problems solved.

[RoadWarrior222]

you know, that could be - it runs decent cold but as soon as it's up to temp it runs like crap. Think that's the CTS?

Not necessarily, just pulling the CTS is a guaranteed way to put it into open loop, and if it runs better like that, it pretty much rules out any weirdness with fuel/spark/mechanicals, and points the finger at sensors/electrics/electronics.

---------- Post added at 06:22 AM ---------- Previous post was at 06:17 AM ----------

Though as pointed out, vacuum issues will cause sensor misreads also.

[gears351]

ok, tonight I'll try forcing it into open-loop tonight. I've got a spare SMEC but it's a 2.2 so I'll knock the initial timing back to 8 if I end up running that.

How long should it take for the computer to pickup a code to give me? I drove it a mile & a half after clearing the codes and it hasn't flashed me anything but the 12 and 55.

[RoadWarrior222]

Some of them take 20+ minutes of warm running and getting up to highway speed.... though I think that's just SDS and lockup codes, but I think there's also an O2 one that takes a while to set.

[Force Fed Mopar]

Try another TPS and coolant temp sensor (one at a time of course). TPS could have moisture in it, CTS could be out of range in colder temps. You can actually check the CTS with a ohm meter, measure the resistance cold and after the engine is warmed up. If you don't have a FSM to reference the specs for it, I (and many others on here) do and can post them for you.

Also check the engine harness connectors for corrosion or loose connections.

[gears351]

if someone could post or pm me the specs I'd appreciate it. I've got a spare TPS to swap in... It really seems to be unable to adapt to a change in the throttle position (I know MAP affects that as well) what about a tach signal?

[turbovanman²]

Tach signal is the HEP so if the HEP is dead, so is the truck.

Codes should set basically right away, if you want to try it, just unplug a sensor and check for that code, but only do one at a time.

[gears351]

Idle was high when cold. Drove till it was warmed up and it was cutting out again.
Pulled CTS, fast idle and was more drivable - now throws 22 code (of course), no other codes though. Disconnected O2 while running and made no difference to idle (didn't think to check EGT at that point) re-connected and checked codes but still just the 12 & 22

Is it ok to pull sensors while running or can I cook something? Any sensor I shouldn't unplug?

[turbovanman²]

You won't fry anything unplugging sensors.

Do you have a scanner?

[gears351]

A Fluke 98 but it's only good for individual sensors innit?

[csxtra]

What are you running for an O2 sensor? Stock or a wideband with a narrowband output connected to the SMEC?

I had a wideband sensor crap out on me last year, and I am using the narrowband output from the controller to feed the ECM. At part throttle it barely ran...no power at all, but WOT (open loop) was fine. Switched over to the stock O2 sensor and it ran fine again.

[gears351]

Stock replacement - narrow band Standard S22 Rockauto was clearancing

[trannybuster]

You left it unplugged?

Yes, mileage wasnt too bad, I bought another and hooked it up, took care of issue.