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Thread: 5.0 HO swap timing issues

  1. #1
    Member Not_your_grandpas_marquis's Avatar
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    Default 5.0 HO swap timing issues

    Hello all! So I did the 5.0 HO swap on my 89 MGM. Car runs good (after a mishap of getting excited and putting battery in backwards. I'm a idiot I know lol) but I have some questions if anyone can help.

    So for the build I did E7 heads (some bowl and port work/smog bumps removed), 86 GT cam (advanced 4° at crankshaft), explorer intake, lightning throttle body/spacer, mustang shorty headers, custom 2.5 x pipe, Borla Pro XS mufflers, factory 2" tailpipes.

    My question, since I have my camshaft advanced 4° at the crankshaft when I go to set base timing (engine warmed up, spout connector out) the car runs like crap with base timing at 14° Advance(which I thought was alot when cam is set at 0/0). When I bump it all the way to 20° base timing it runs great (no back firing, no knock/ping) and actually has some power out of the hole with the weak 3.27 rear gears.
    So is 20°Advance to high for base timing even tho I'm having no I'll side affects? Is it taking so much base timing since my camshaft is advanced?? I can bump it all the way to 40° Advance base timing at idle and I still get no knock/pinging, backfiring, or anything reving or even when turned off and spout connector plugged back in and taken for a drive. Is my TFI module trashed or what?? I'm stumped why it's being weird.
    Sorry for the long read, just want to be thorough. Thanks for all replies in advance.

  2. #2
    Lost and driftin' Arquemann's Avatar
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    My CFI lopo ran like garbage for quite a bit, eventually I changed my TFI another time and the issues disappeared.
    Mine ran like total crap with the spout on, it did still accelerate smoothly. Ran fine with the spout unplugged. Never had any pinging in any configuration and I even run regular gas. My stock cam is 4° advanced and the base ignition timing is 10° for my engine.

    When your base timing is "correct", how does it run with spout plugged in? When it runs rough, is it just idle and low rpm or does higher rpm run crap too?
    1985 Mercury Grand Marquis LS, "Maisa"
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    GMN Regular DerekTheGreat's Avatar
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    You're hot rodding it. Factory suggestions are out the window now. Now, without a dyno or knock counter to see results, it's all about the butt dyno and what not. So if it seems to like your changes, go with them.

    Everyone says an HO is a dog out of the hole compared to a LoPo in a box. I disagree- I think they're the same, only the HO doesn't put you in your seat like the LoPo does.
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    Member Not_your_grandpas_marquis's Avatar
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    With spout plugged in, runs pretty good at 20° advance base timing. Alot more pick up out of the hole. No back firing under slight throttle, idle is alot lower and smoother at idle. (From 1100 at idle to 850/950 it's at now). I checked timing with spout in and it advances as it should I just figured it's super high initial timing because from all my Mustangs and Mark VII's I've had 14° advance was maxed out but I also had the cam set straight up not advanced at all.

  5. #5
    P31 Pursuit Car Brown_Muscle's Avatar
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    The problem with having the base timing so high, is that the entire spark table is shifted higher. You could be running a crazy amount of timing at WOT, which could cause problems you might not even hear. I assume you're using a timing light to verify timing? Normally I'd say the dizzy is off a tooth. Did you re-use the balancer? It's possible the out ring has spun a little and is showing you the wrong timing.

    Re-read it... if you're at 14* with the spout UNplugged, I wouldn't worry about it. I thought you meant 20* with it unplugged. It won't run the best at 10* with the spout unplugged, so if it is set to that, and then you plug the spout back in and it runs well...thats normal
    Last edited by Brown_Muscle; 04-09-2021 at 11:59 AM.
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  6. #6
    Member Not_your_grandpas_marquis's Avatar
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    Yeah for sure Derek, it definitely changed when I went from 14°A initial to 20°A initial timing. Once I put spout in, took it for a drive it actually kinda barked floored from a stop and pulled nice to 5500. My LoPo was a dog, wouldn't set you back anywhere that's why I was so excited to slap the HO together and get it in. I know the car definitely needs a converter now, that's the next thing along with a cooler (I have baumann shift kit and sonnax valves in the trans now) to get the full effect of the HO since the stall is so low for the LoPo.

  7. #7
    Member Not_your_grandpas_marquis's Avatar
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    Exactly what I thought Brown_Muscle, that's why I was worried about it being so high tho it is running like a champ now. I know for sure it is not a tooth off, I dropped dizzy in when I was assembling the engine and had it at TDC on compression stroke. Even verified when I was having the trouble starting from the battery mishap. It runs really good,it has just been a straight dog out of the hole until 2500rpm then it picks up, plus the backfiring at slight throttle. Looked up signs of timing is issues and I had every sign of timing set to retarded and needed more advance. I used all new parts for my rebuild (minus heads, cam, intake.) Has a new pioneer balancer and ARP crank bolt to secure it.

  8. #8
    I'm an air-conditioned gypsy gadget73's Avatar
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    are you sure your balancer and pointer is accurate? 20btdc sounds like a lot to me. I've had mine idling that far advanced and it sounds strange. Mine all ping and carry on much past stock so they sit at 10 BTDC. Advancing the cam 4 degrees shouldn't have all that much effect on how it idles, certainly not enough to make it idle badly at 14 BTDC.

    think I'd stick a pokey thing down in #1 and confirm TDC does in fact match TDC on the timing marks. A dead stop is more accurate, but just a screwdriver and a ratchet should be enough to tell if the pointer is off enough to matter.

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  9. #9
    Member Not_your_grandpas_marquis's Avatar
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    Yes, it is a factory pointer. Not bent at all since it came off a virgin 120k 5leaker. All new parts except for the factory Ford head castings, intake, and camshaft. Pioneer balancer, that's the one I always used for the factory upgraded 302 I do. I've bumped it over until it blew my finger out and set it at 10°btdc on the balancer. Sofar it has been idling better than it has at 20°A initial timing. No popping, pinging, or backfiring. Getting better gas mileage (tho it was never that good hahah), and way better out of the hole performance as it would just slowly accelerate and then take off once it hit 2500rpm.

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