I have had a long running problem w/ my 90 Bronco w/ 302 V8 w/ 140K miles, and decent cylinder compressions. Engine would start well, but would usually stall several times w/o lots of throttle feathering. After a short initial period, it would run very well until engine warmed fully. At which point, it would "sag" when throttle was applied moderately and frequently lightly backfire through the throttle body. Under full throttle, it accelerated and ran well. No engine codes were ever displayed.

After testing nearly every sensor and system on the engine; MAP, EGR, ECT, ACT, PCV, TPS, O2 etc. w/ negative results, this morning I decided to check the electronic timing advance. You simply measure a voltage at the SPOUT connector to be w/i 30-70% of full system voltage. This checked OK, but I noticed the engine (cold) would not idle and as I was feathering throttle to keep it running, it backfired lightly. Since disconnecting spout fixes timing (no advance or retard), I wondered if retarding the timing might improve the idle. Since it backfired, it the timing retard might not be adequate.

Timing had been earlier repeatedly checked and set to spec of 10 deg BTDC. This morning, I lowered timing to 6-8 BTDC.

Engine now idles stable, acceleration is fine, and backfiring has been eliminated. What a sweet feeling of relief!

I'm not exactly sure why this fix worked, but suspect that as an engine ages, it may need a reduced timing setting for best performance. Wear of the timing chain and camshaft may also affect the need to reduce timing.

This engine has also been pumping oil thru the PCV air intake into the air filter box, primarily due to the backfiring and very low (negative) vacuum when the "sag" during attempted acceleration. I suspect the oil pumping will be much improved, but it's too early to be sure.

If your 302 V8 has some of the same problems, you might try reducing the timing 3-4 degrees and see if that helps.

Regards

 

Thanks...what did your idle RPM level out at?

 

At cold start it intially starts at about 1500, and fairly quickly comes down. It stabilizes about 700-800.

Starting from cold is also much improved. It would always die almost immediatetly unless the throttle was feathered. Now it will run stable w/o throttle and gradually idle down. A big improvement.

regards

 

so actually you advanced the timing 2 to 4 degrees. does this give you any pinging while pulling hills or heavy accelleration? how about a power increase did you notice any differance?

 

I would say I retarded timing, 10 deg Before Top Dead Center (BTDC) is spec, and I set timing to 6-8 degrees BTDC. Spark occurs later in compression stroke, so timing is retarded.

regards

 

Oh, there is no spark knock, but you wouldn't expect this w/ retarded timing. That was an issue at 10 BTDC.

regards

 

What exactly is spark knock?

 

I am no expert but it sounds like your harmonic balancer is off a little causing it to look like you are actually set at 10 degrees where as in reality, it was set at 14 or so degrees. This happens on older vehicles since the inner rubber seal can slip or something like that.

Either way, glad you got her running again.

 

I'm not sure how the 302 harmonic balancer attaches to the crankshaft, but most engines use a keyed slot to insure alignment of timing marks on balancer.

It might be the timing chain is installed off 1 link. This would definitely change timing setting, and perhaps the camshaft timing error would not be so large as to cause problems. I'm not about to go after the timing chain to check, since it's running fine and my son is happy.

Yes, it's been a long struggle. Truck ran OK till head gaskets failed w/ water in oil, oil in water. I pulled the distributor when I installed new cylinder head gaskets in early 2002. It's been running poorly ever since. My son was ready to throw in the towel and sell the Bronco. I knew there was something simple wrong, but what!

I think Sherlock Holmes said something like "When all other possibilities are exhausted, that remaining must be the solution,... no matter how unlikely" or something like that.

regards

 

I have the same problem. But I put a 1996 Ford Bronco 5.0 engine into a 1992 Ford F-150 5.0. body. Two Big differents is the Cranshift senor is mount at the bottom buy the harmonic balancer. The 1992 Ford F-150 don't have a crankshaft sensor. It is a electronic conrol Module mounted on the driver side panel under the Brake master cylinder. The Second differents is the air charge temp sensor that is mount on the air filter housing.

 

The hub of the balancer is keyed
The outside malleable iron inertia ring is mounted in rubber, and that is what slips, with the timing marks on it
Few and far between IMO but does happen
You guys know about the octane service pin right? TexasBronco?
The one that causes a code 341 if removed?
I believe the earlier ones (Your 1990) had the service pin but no code if removed

 

20 year old thread brought back from the dead. TexasBronco hasn’t been active since 11/03.

The ‘96 is mass air OBD-II while the ‘92 is speed density OBD-I. They are two completely different operating systems which is why the sensors were not the same. You cannot mix the two systems.