Difficulty timing a 1995 Chevy 454ci

On the side of the throttle body is the idle air control valve. It acts like a choke. If it is clogged by carbon build up engine will not run very well. Held on by two small screws. be careful not to break them, I know because I did!
Even dropping distributor in off one tooth engine will run but lack some performance!

enblethen wrote:
OP: you need to recheck the distributor. rotate the engine to number one cylinder, align the timing mark on the vibration damper. It may be off one tooth.
Installing distributor can be tricky! the oil pump shaft doesn't always drop right in meaning the engine needs to be turned over one direction or another. Best to do manually with bar on crank or if lucky with serpentine bely.

I verified the harmonic balancer is good and has not slipped. I posted it earlier in the thread but I took a 1/4 extension and slipped it into the spark plug hole on the number 5 cylinder, then rotated the engine until the extension was jammed in place by the piston coming up. I then checked the balancer and found it approaching 4 degrees BTDC, so the balancer is safe to use as a timing mark. That's how I got it running again. I have adjusted the timing by ear by turning the dizzy to where it will crank when you just bump the key and it will start hot or cold, which is a big improvement.

However, it's still running rough and pig-rich. That's why I want to verify all the sensors and get a timing light on it to really get the timing as precise as I can.

Based on how it runs it may be down a cylinder so I still need to verify that as well. When I changed out the spark plugs the plug that came out of cylinder 7 was pretty fouled with oil, so the oil control ring on that cylinder is pretty worn out. That one might be down.

It also looks like at some point in the RV's life the catalytic converter was removed. The O2 sensor is still there, but I don't see the cat. That could also be a piece of the lovely smell problem coming from the exhaust.

I haven't done my audit of electrical grounds yet, was focused on getting it running. I agree that bad grounds cause strange behavior. I had an Outback that was a crusty northern car and it ate headlight bulbs and shifted really rough until I cleaned all the grounds. The battery cables can probably stand to be replaced, but I'll get there.

I also need to go through the general wiring as the electric fan on the radiator doesn't seem to be running once the engine gets to temp and it sounds like the mechanical fan needs a new clutch. I also haven't seen the tiny engine bay cooling fans kick on either. Plenty of work to do in order to get this one sorted.

Does anyone know what color spring is needed for the 94-95 FPR? I can find plenty of kits with springs that claim they work for 94-95, but they also claim to work all the way back into the 80's model years so I don't know how that is possible with the change in fuel pressure in 94-95.

As long as you guys are willing to offer wisdom, I'll offer updates. This is my first GMC engine and chassis so much for me to learn here.

Indeed re-check the distributor. When removing and/or reinserting it if you watch the rotor closely you will see it turn. Often times upon reinserting it will be off 1 or more teeth.

How's the engine-frame ground cable?

This has caused many headaches for TBI owners trying to chase down strange electrical gremlin/s. Only to find out it was a less than stellar ground cable. Also check and/or replace the battery cables.

Good luck and keep us posted on anything new.

OP: you need to recheck the distributor. rotate the engine to number one cylinder, align the timing mark on the vibration damper. It may be off one tooth.
Installing distributor can be tricky! the oil pump shaft doesn't always drop right in meaning the engine needs to be turned over one direction or another. Best to do manually with bar on crank or if lucky with serpentine bely.

OutofTime wrote:

enblethen wrote:
What new distributor?
OP: you never answer as to whether your removed the distributor to install parts.

I thought that I did. The wires to the pickup sensor in the dizzy were bad, so I did remove the old dizzy and install a new one. At that time I stabbed it close enough that the engine ran. The strange thing is that I got it towed home, it fired up the next morning (all on new dizzy), then it wouldn't fire that afternoon.

Then came the week of me troubleshooting and being a dingus who didn't line up the button with where the wire connection to the cap, instead pointing the button at the cylinder I wanted to time from.

Current status is that it's running now, but that's it. I have not had time to dial in the timing or do any other investigative work since I got it running two weekends ago. I should have more time this week to check stuff out.

I was reading the pressure was different in 94-95. The trick is finding a kit that has the right pressure spring. I do intend to look at the FPR as I imagine after 250K+ miles the spring is tired or the diaphragm is toast. I also intend to very the IAC,TPS and MAP are all working as they should. This is my brother's RV and he doesn't have the money or inclination to drop a new 454 in so it's going to be patch this one best that we can until he can save up for something nicer.

enblethen wrote:
What new distributor?
OP: you never answer as to whether your removed the distributor to install parts.

I thought that I did. The wires to the pickup sensor in the dizzy were bad, so I did remove the old dizzy and install a new one. At that time I stabbed it close enough that the engine ran. The strange thing is that I got it towed home, it fired up the next morning (all on new dizzy), then it wouldn't fire that afternoon.

Then came the week of me troubleshooting and being a dingus who didn't line up the button with where the wire connection to the cap, instead pointing the button at the cylinder I wanted to time from.

Current status is that it's running now, but that's it. I have not had time to dial in the timing or do any other investigative work since I got it running two weekends ago. I should have more time this week to check stuff out.

enblethen wrote:
What new distributor?
OP: you never answer as to whether your removed the distributor to install parts.

Fuel pressure for the 94-95 454 TBI years was 26-32psi. Earlier years was 9-13psi.

If it isn't getting spark it will be the ICM. It must be functioning correctly for the injectors to pulse fuel.

If you plan on rebuilding the TBI be careful when removing the (4) screws that hold the pump diaphragm cover in place. The spring has a lot of tension if not ready for it.

What new distributor?
OP: you never answer as to whether your removed the distributor to install parts.

Bikeboy57 wrote:
First, I too was recently bitten by the GM distributor design that routes the circuit across the cap for #1 cylinder. Fought it for two days until I saw the wiring runs inside the cap.

A trick I used to see what was going on was to use a spark plug tester on #1, place the tester close to the timing mark on the engine, and video the spark as a helper tried to crank the engine. Frame by frame replay showed me how far the spark was off.

Did your new distributor have the little timing mark on the base to align the rotor with when reinstalling the distributor in the block?

Nope. I set it all in the old school way. I haven't had a chance to refine the timing yet. Once I do that I'll probably take a look at the FPR to see what kind of shape it's in. I suspect the spring is toasted at this point.

First, I too was recently bitten by the GM distributor design that routes the circuit across the cap for #1 cylinder. Fought it for two days until I saw the wiring runs inside the cap.

A trick I used to see what was going on was to use a spark plug tester on #1, place the tester close to the timing mark on the engine, and video the spark as a helper tried to crank the engine. Frame by frame replay showed me how far the spark was off.

Did your new distributor have the little timing mark on the base to align the rotor with when reinstalling the distributor in the block?