Community Forums

flht95 · 08-20-2016, 06:03 PM

I have a 1992 Pace with 454 and TBI. I also have the chevrolet chassis manual that came with it. The problem I have is that the picture in the manual showing the lower tab shows it on the LH side at 7 o'clock (and the verbiage references the LH side of damper) It then goes on to say use plugs 5 or 8 when using that tab. Unfortunately when I get under the MH my tab is at the 5 o'clock position if I disconnect the the wire to the distributor (that is supposed to be disconnected to time), hook the timing light to 5 and look where current timing is it looks like ts over 12 degree advance (and the motorhome is running good) . If I then adjust the timing to 0 degree, when I try to drive it it backfires very badly. I SUSPECT the issue is which spark plug I am using - can anyone hlep?

bill06447 · 08-20-2016, 07:43 PM

First thing is make sure the distributor is good-because of the (lack of) oiling to the distributor the bushing wears rapidly and the shaft wobbles and the engine will never stay in proper timing. On the plus side new distributors complete with coil and module can be had for under $100. The tan with white stripe wire needs to be disconnected from the distributor before static timing (the wire usually has it's own connector in-line to make this task simpler). Good luck these engines are a PITA to time even in easily accessed truck and car applications.

speed racer · 08-21-2016, 06:41 AM

Earlyer chev engines time off of #1 or #6 cyl. They put the indicator on the bottom to make it easyer to see in this application.

flht95 · 08-21-2016, 06:55 AM

Actually, I got the desire to do my timing after battling a lack of power and backfiring under load issue for that past 2 years and replacing multiple items (Plugs,coil, ecm, knock sensor, replace vacuum hoses, EGR, distributor module) and rebuilt TBI only to find that the INLINE FUEL filter was partially clogged. THe haynes manual nor Chevy manual ever suggested that! Found that recommendation in some chevy truck forum. I've worked on cars 47 years and never had a fuel filter cause me that problem. Once I replaced the filter it runs like a champ!

actually accellerates up hills it use to backfire up. When it had the problem in the past I was advancing and retarding the timing trying to eliminate the backfire. Now that that problem is gone I want to set the timing to its correct point for best performance. Distributor is good and I am disconnecting tan wire to do the timing. Again - the gm instructions show (and state) a different timing tab location (7 O'Clock) than what my unit has (5 O'Clock) If I ignore that and use the plugs they state for timing (5 or 8) and set the timing for 0, the unit has no power and backfires under accelleration on flat ground. BEFORE I tried to adjust timing I checked to see where it was and it was easily 12-14 advances WITH THE STATIC SPARK WIRE disconnected. I SUSPECT the plug I am using for timing is not the correct one (Tab location is different so the plug ought to be also) The firing sequence of this era V8 CHevy 1-8-4-3-6-5-7-2. and crank turns twice for each revolution of the distributor (which is why they suggest 8 or 5 for the timing spark plug) Based on that I BELIEVE that 4 or 7 would be the correct plugs to use IN MY TIMING TAB LOCATION (ie 5 O'Clock). Can any validate that OR tell me why it won't run at 5? PS this has turned into a knowledge quest. The unit itself is running great since I replaced the fuel filter and put the timing back to where it was - although I would like to get it exactly to factory specs.

bill06447 · 08-21-2016, 08:05 PM

You always use #1 spark plug for timing on these engines, the tab and balancer mark location do not matter-if there are two tabs on the cover there will be two separate marks on the balancer. Which brings another point-if the harmonic balancer has shifted due to deteriorated rubber the marks won't line up properly. (I have this issue with my Ford pickup 300-6 it gets timed by ear).

dieselclacker · 08-22-2016, 06:55 AM

You can use either #1 or #6 plug wire to set the timing on your engine. It would probably be more convienient to use #1 wire regardless of which timing location you choose to use. The 5 o'clock position is for use under the motorhome.

F4Gary · 08-23-2016, 08:48 AM

A lot of us classic car guys use vacuum to time our engines. Not sure if it works with a '94 TBI, but we time to max vacuum at idle.

scdiver · 08-23-2016, 09:05 PM

I just went through the same problem with my 96 Aerbus. I found that I had to use the number 8 plug wire to time it, the number 5 wire, that is easier to reach would not time the engine correctly. You also must unplug the timing wire.
Try setting the timing to 4 degrees before 0.

At the suggestion of a truck mechanic, the first thing I did before doing the timing I described above was to take the mh for a test drive with the doghouse cover off and the distributor just snugged down. I drove it till the back fire started then pull over and advance the timing a little. I did this till the mh ran correctly then I took it back and set the timing to the correct specs. The next test run had the mh performing correctly.

Good luck

kennyrodgers · 08-26-2016, 12:00 AM

Hi there,
I have a 94 TBI so assuming the 92 is the same.......

Timing is set from No5 plug when doing so from underneath. I'm not sure about the 92 but the 94 454 TBI is 4° BTDC, the ECU controls advance / retard from there. If you're at 0° it could be the cause of your backfire
If you can find your emissions label the info for your engine should be on there, mine is on the air filter housing.
Cheers and good luck.

70ChevelleSS · 08-26-2016, 06:12 AM

Quote:

Originally Posted by bill06447

You always use #1 spark plug for timing on these engines, the tab and balancer mark location do not matter-if there are two tabs on the cover there will be two separate marks on the balancer. Which brings another point-if the harmonic balancer has shifted due to deteriorated rubber the marks won't line up properly. (I have this issue with my Ford pickup 300-6 it gets timed by ear).

That's just not true. If you move the tab from 1 o'clock position down to 5 o'clock you obviously can't continue to use #1. #5 is the correct plug if the tab is at 5 o'clock.

A chevy big block will run like a pig at 0* advance. Even 4* is not enough advance. Our previous MH, 94 454 TBI, ran great once I advanced the timing up to around 12*. On my Chevelle I run 18* advance. I don't know where Chevy engineers came up with 4*. They even say 4* advance on their GM Performance crate engines. Our neighbor purchased one and it would overheat idling for a few minutes with timing at 4*. We retimed to 18* and runs cooler and much stronger.

kennyrodgers · 08-26-2016, 08:21 AM

From what i can gather 4° was something to do with getting round emissions although I'm not 100% on that.
I researched the hell outa this when mine was running like a dog. The very common misconception is 0° with the wire disconnected but that's definitely not the case with my 94.
Personally, I'd be worried about advancing it to 12° in a Motorhome due to the extra weight and rubbish gas compared to how it used to be but I can see your point. I've toyed with the idea of advancing it slightly but after all the problems I've had I'm happy she's just running smooth and staying cool.

Happy days.

Oemtech · 08-26-2016, 08:24 AM

I have done it like scdriver... drive, advance, drive advance till it pings and back off a tad. Now back to the shop and see where I am at with a timing light.

70ChevelleSS · 08-26-2016, 01:35 PM

You definitely don't want too much advance but these are low compression engines and can take more than 4*. Most also have knock sensors which will retard the timing if it starts to ping. Anyway mine ran great at 12 or maybe it was only 11, it's been a few years.

bill06447 · 08-26-2016, 05:49 PM

Quote:

Originally Posted by 70ChevelleSS

That's just not true. If you move the tab from 1 o'clock position down to 5 o'clock you obviously can't continue to use #1. #5 is the correct plug if the tab is at 5 o'clock.

If "you" moved the tab this may be true but if there is only one tab, the mark on the balancer will coincide when #1 fires. My 91 tells you on the emissions label on the air cleaner to use #1 plug, as well as every shop manual I've peeked in. Some Fords have two tabs and also have 2 marks on the balancer but that's a different animal...

Whenever in doubt use the label on the vehicle, it was put there for a reason