I've been having several issues with my 88 Lebaron that I picked up in June. I've had a few 2.5L NA cars in my life and wanted another Lebaron since I sold my 87 about 13 years ago. I've spent countless hours on the forums reading. I apologize for the long post but will try to cover everything in detail...
Mods include: 2.5L CB, forged pistons .020 over, balance shafts removed, 3 bar map, 52mm tb, ported 2 piece intake, TU header with big turbo, 3" swing valve and exhaust, cat, FMIC, 'Chipped SMEC using a Rob cal from D-CAL' and currently a stock swirl head with PT lifters and a recent valve lap. The trans is a 568 in a 523 case with a 4 puck ceramic clutch. Walbro 255 with AFPR, TU rail and +40's (currently stock T2 injectors).
The (current) problem is: Usually stalls immediately after start unless I keep blipping the throttle for about 30-60 seconds when the idle evens out. It will then idle with constant misfires and exhaust popping. Vacuum is 16-18Hg and will creep down to 10Hg when it's stumbling bad. When the idle is rough and the vacuum is low the open throttle body (intake pipe disconnected) sounds like a noisy vacuum cleaner. The 3-bar MAP signal reads OK. The wideband is pegged at 16 (lowest it goes).
If I unplug the MAP before starting it will start fine and idle and rev perfectly. If I unplug it while idling the idle smooths right out. The throttle body is quiet with the MAP unplugged. The vacuum is 18Hg. The wideband reads in the 12-14 range at idle. I've bypassed the baro with no change. I've reduced the vac system to the AFPR, MAP and Auto Meter gauge. I'm confident there are no vacuum leaks. With the MAP unplugged it idles smoother than ever.
I've verified cam timing several times and ignition timing is set to 12*. I can play with the cam timing about 5* or so either way with the adjustable cam gear without much difference at idle. If I go much beyond that it won't stay running or start at all. 12* on ignition is the sweet spot. With a timing light on the flywheel and the coolant sensor unplugged the timing stays pretty well on 12* with an occasional blip to 16* or so.
I've swapped the whole throttle body with TBS and AIS. I read that the TPS shares a ground with the MAP but haven't verified this. I've swapped +40 injectors out for stock T2 injectors and reset FP to 55psi. Fuel pressure is good and holds for an hour+ after shutdown. I did have issues running pig rich with the +40s until I reduced the pressure down to <30psi which concerned me.
There is no change with the o2 sensor, air charge temp sensor or AIS disconnected. I do have a new o2 and coolant temp sensor on the bench.
I have had other problems leading up to this which shared some of the same symptoms but I have been working through them. The engine always ran strong out of idle and had lots of power right up to the MBC setting at 12psi.
Another issue I've had leading was bucking while cruising in gear. This may have been resolved with the new injector harness but I haven't had it out of the garage since to verify. It also had an idle surge which seems to be gone except occasionally when I disconnect the CTS.
Any insight or suggestions would be greatly appreciated. I'm hoping to get this running right before it goes away for winter.
