Bronco II--runs poorly (long post)

[DAD-Fick]

I have a 1988 Bronco II 4x4 with 5 speed manual transmission. 2.9L EFI 6 cylinder. EEC-IV/TFI ignition system. The odometer reads a "very" crooked 25+k miles---I suspect it is at least 125+K miles.

PROBLEM: Upon cold start-up, engine chugs and shakes until given a little throttle. As it warms, the engine seems to idle fine except that it lopes like it has a racing cam. When accelerated, it hesitates, chugs and bogs, then at about 2000 RPM it smooths out. There is an intermittent drop in idle to an almost and occasional stall--when throttle is opened and closed quickly this symptom can be usually be duplicated. Warm start is easy with no cold start symptom--the rest remains as stated. When put in gear and as the clutch is let out, the engine stumbles and shakes terribly, and has little or no power--it usually stalls. It can't really be driven down the road to see what happens in higher gears.
The exhaust is normal light white and no unusual smell. It seems to have excessive condensation at the tail-pipe (water but no antifreeze). I will attribute this to the fact that the entire system is not being heated high enough to vaporize all moisture. The engine is getting warm enough for the heat to circulate within the cab interior.

Before I got it, the vehicle had set for at least 3+ years (but the registration in the glove box expired in 1995). The fuel injectors had "allegedly" been replaced prior to storage, but the vehicle had not run since (or before?). The external fuel pump had been removed, and the fuel tank was contaminated (nasty liquid). The water pump appears to be new.

(cont in next post)

[DAD-Fick]

Here is what I have done so far and the order in which I have done it:

1) drained cleaned the fuel tank

2) new internal fuel pump/sending unit

3) new fuel filter

4) new external fuel pump

5) PREMIUM fuel in tank

6) tune-up (plugs, wires, distrubutor cap, rotor, air filter, oil and filter--PCV rattles freely on shake test)

7) new timing gears and chain (old one was ORIGINAL)--timing all set to marks & TDC on reassembly and verified afterwards.

8) new ignition start module (it would only run when cranking--test found old one to be bad)

9) oil additive in the event of stuck valves (removed appropriate amount of oil prior to adding)

10) 1/2 cup Marvel Mystery oil in fuel tank (to lubricate potentially dry fuel system components).

11) new Throttle Position Sensor


I have experienced a similar run condition with a different vehicle and had to replace the MAF sensor; this engine does not seem to have one. Other than to bring the vehicle to an actual running state, not much has improved after all has been performed. I am at a loss, and really would like to be driving this vehicle as it is costing me so much money and time. PLEASE SEND HELP!!

[ToughNut]

I would do a compresion check as well as a cooling system presure check. It sounds like a possible head gasket, pulling the plugs out and looking for moisture is an easy way to tell allthough not allways prominent, try running the engine at 2grand for about 3-6 minutes then let it cool a bit before pulling a plug or two (one off each side should suffice) also note if steam begins to come from the exhaust. let me know what you find ... if nothing else look for craked or missing vacuum hoses/plugs on your t's. Good luck!

~Tough
You can take your horse to water but,
you can't make it swim!

[mrshorty]

I had similar symptoms from a bad O2 sensor. Have you pulled any codes or tried any of the EEC-IV self-tests? Checked fuel pressure? I also recall a TSb that applied to my '87 that attributed symptoms like that to a dirty IAC/throttle body/upper intake.