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TBI 454 Troubles R/V

H

Heatseeker

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San Joaquin County, CA.
Hi all. I'm new to the site. I found it while searching for answers for my troubles. I read a lot of good info here so I thought I'd join to see if I can find the answers I need.

I bought a 95 Southwind late last year. It is built on a GM P90 chassis powered by a 454. The first few times out, I noticed it had a miss. It would mostly occur when I was stating to lug the motor. Like when just starting up a grade. Once I would throttle up and the transmission would kick down, it was no longer noticeable.

I finally found the time to put a tune up on it. I changed the plugs, wires, cap and rotor and the air filter. When pulling the plug wires i found no.8 wire burnt pretty bad. I figured i had found my miss! Now, when I start it, there is a hint of a miss @ idle. Once it is put in gear, there is a pretty noticeable miss present. Once underway, it runs like crap. If I demand much from it, it will pop out of the throttle body and sputter. It will still run, but rough. It runs worse now than before.

I'm no stranger to 454's. I have one in my boat, but it has a 8-71 blower and a couple of carbs on top of it. Whole different animal.

My injected knowledge is pretty limited. So I'm here. Have any of you had similar issues with these TBI engines?

Any help is genuinely appreciated.
 
Definately check the fuel pressure first.
Then double check timing. Backfire out the intake is a timing issue

Anyway you could do a video of it popping and missing? Not sure what is happening with "popping" if it is backfire or loading up.
 
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.
 
THEFERMANATOR said:
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.
Click to expand...
Whoops, forgot it was and RV.....
 
Yeah, once the fuel pressure and timing is known good, WarWagon's (iirc) reminder of timing light on the injection pattern is next thing to look at.
After that, it's back to my favorite wet & dry compression tests, and leak down test.

I'm too old to remember- when did GM stop with the stupid plastic coated timing gears? I remember that plastic would break off and cause enough wacky timing to give light backfire scenarios, but still run otherwise.
 
A bad fuel pressure regulator is common on the TBI. I had bough up a batch of re-manufactured 454 TBI's from u-haul back in the day because of throttle plate shaft wear etc...for my 454 Burb.
 
Reminds me of a 350 TBI EGR hard to find intermittent problem we had. Vac operated EGR on this engine? (Any EGR? 1993+ Electronic ones stick open depending on CA emissions, whatever, it may have electronic.) Drop it in gear and see if it (EGR valve) flops full open - if so replace it. The vac signal to the EGR is on/off period. Back pressure and vacuum work a trouble prone valve in the EGR to control it.

Note: Going "lean" will cause the High Voltage to find a new way to ground and may burn up wire sets as a symptom to another problem of going lean.
 
WarWagon said:
Reminds me of a 350 TBI EGR hard to find intermittent problem we had. Vac operated EGR on this engine? (Any EGR? 1993+ Electronic ones stick open depending on CA emissions, whatever, it may have electronic.) Drop it in gear and see if it (EGR valve) flops full open - if so replace it. The vac signal to the EGR is on/off period. Back pressure and vacuum work a trouble prone valve in the EGR to control it.

Note: Going "lean" will cause the High Voltage to find a new way to ground and may burn up wire sets as a symptom to another problem of going lean.
Click to expand...
Yep, EGR can be a PITA too.
 
Thanks for all the tips.
The poppong is occuring under acceleration, kind of randomly. I'm pretty sure if backfiring through the throttle body.
I should have done a comp check when I had the plugs out. I have to jack the thing up, remove the front tires and remove a couple of shields to get to them. I am assuming that I don't have a burnt valve since the running condition changed so drastically with a simple plug/wire/cap/rotor swap. But anything is possible...
I'm going up to get it from the storage spot next week. That is half the problem, it's an hour away. Once it's home, I will run through all the checks suggested. The timingn disconnect is supposedly at the distributor on this chassis.
Maybe whn I get it back here I'll post a video.
Thanks again.
 
Make sure you have AAA or some towing plan for the large beast it is. GM likes to give warnings before it leaves you on the side of the road. IMO take your tools with you and work on it in storage. Then decide if it will run an hour home...
 
If there was a big change right after you changed the wires, I would look over everything again. With those symptoms the first thing I thought of was a crossed ignition lead, then after hearing how hard it is to get in there to work on it that sounds like it could be really easy to get a wire crossed.
 
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.
 
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Burnt valve should show in compression test.
Another thing I noticed is that when connected, my timing light falters with the engine. So I hooked the spark pick up direct to the coil. Same deal. I took the ignition control module to the parts house and it checks OK. But I'm wondering if their test is thourough enough?
 
Timing light cutting out at same time engine does is loss of ignition.

Pull the cap off and check distributor for free play.

Add a jumper wire from the hot side low voltage power supply to coil to a light bulb you can see on dash. See if the light bulb fluters when the loss of power occurs. Is so chase the power supply like a bad connection somewhere. If not gine then coil, distributor, etc.

Dont discount the possibility of a burned intake valve. 1 valve can be slightly burned and lose very little compression. Then when the load is on the engine, it can present itself. Did you do a leakdown on it when you did the compression test?
 
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