TBI 454 Troubles R/V

[THEFERMANATOR]

A weak coil is fairly common on these engines if it's the coil with 2 plugs and 4 wires going to it. If its weak, it will cause all kinds of popping as well as problems setting your timing. I normally get the msd replacement and put back in them when I have problems.

 

[FellowTraveler]

Hers what I found out messing with this thing all morning:
1. No.8 wire was burnt again. It was missing the sheild. I replaced the wire and made up a sheild.
2. Compression is good. 140-150 across the board.
3. Timing was off 1.5*. Reset to 4* BTDC with jumper disconnected.
4. Injector spray pattern is consistent on both injectors.
5. Fuel pressure is about 40 psi at the filter. I used a hokey hose and clamp set up to get this. Filter is clear.
6. Firing order is correct.
7. This thing still runs like crap.
8. EGR is clean and appears to be functional. It is electric, so I can't see what state it is in when running.
I tried to upload a video without success... basically, idle is fairly smooth and acceleration is normal in neutral. Once in gear, motor shakes pretty good. Once underway, I get stuttering and pops through the throttle body on acceleration.

FP for TBI should be between 12 & 15 psi if my memory bank is correct...........

 

[NVW]

Does this engine have an O2 sensor? I had a bad one and it ran rough, smoked and mileage dropped from 12-3 mpg.

 

[THEFERMANATOR]

Finding the tim8ng wire can be tricky in rv chassis's. One thing I found is you must use GOOD plug wires with them because of the heat. Also only use ac delco plugs in it. Checki,g the timing is a good place to start. Fuel pressure on that engine I believe should be 30-32 psi whereas other tbi engines were 8-13. A timing light is almost a requirement to work on that beast. Not just for setting the timing, but also to check injector spray pattern. A compression test would also be a good idea as rv's are known to burn valves from all the heat from lugging all that weight around all the time.

FP for TBI should be between 12 & 15 psi if my memory bank is correct...........

Not on 94-95 454's. His pressure still sounds a bit high to me, but not abnormal as I believe they can go as high as 38. MANY people have been thrown off by the 94-95 454 TBI's as they used a TPI pump in the tank and small injectors due to the increased fuel pressure. I know about them as GM used 454 TBI units on all there marine engines, and I used to do alot of boats.

 

[Heatseeker]

Well, I give up. After spending the last 12 hours in and under this beast, I have to say I'm beaten. Since my problem appears to be ignition related, I swapped out the ignition control module and the coil with no improvement. $70 down the tubes.

Anybody want to buy a really nice 95 Southwind? It has a small misfire condition...

 

[ak diesel driver]

Put a vacuum gauge on it while you drive and post back the results

 

[Will L.]

I take it no freeplay in the distributor when you swapped the module.
Any result from the lightbulb test?
If those two turned up nothing, AK's vacuum gauge was the next test.



Quit buying parts and finish diagnosing it.

 

[FellowTraveler]

Not on 94-95 454's. His pressure still sounds a bit high to me, but not abnormal as I believe they can go as high as 38. MANY people have been thrown off by the 94-95 454 TBI's as they used a TPI pump in the tank and small injectors due to the increased fuel pressure. I know about them as GM used 454 TBI units on all there marine engines, and I used to do alot of boats.

Thanks FERM, I figured you would know.

 

[Heatseeker]

I will be driving this thing today. I am going to hook up the light to the coil before I go. It has a vacuum gauge on the dash, so I'll keep an eye on that as well.

 

[Will L.]

Meant to say testlight btw. I Must have bumped my head.

 

[Heatseeker]

Just hooked up the light, hopefully to the correct plug on the coil. Since it was suggested to connect to the low power side of the coil, I connected the light to the smaller red wire that comes out of the distributor. That is the low speed coil control according to the factory manual I have acquired. The light stays on and steady through all rpm ranges sitting in the driveway. Vacuum is at 21-22 inches at idle with just a hint of flutter in that range. Probably the miss causing that. Taking it out later...

 

[udidwht]

I'd bet it's either the pick up coil in the distributor or the ring stator in distributor is cracked and or loose. Replacing both requires removing the distributor. Fuel pressure for the 94-95 TBI is 26-32psi and the RV is on a GM P-30/32 chassis.

One other thing to check...

Cooling temp sensor. When it goes bad it will generally go into dump fuel mode and can cause the symptoms your seeing as well.