Engine and Transmission Tech

I hadn't noticed before probably because use was pretty limited to some short, neighborhood type errands... but, when I drove to cars & coffee last Sat I noticed a definite missing at cruise (1800-2200 RPM range; wasn't on the highway).

Given that, here's what I'm thinking:

1. Retorque intake & headers - don't think they've loosened because I retorked them recently but, worth double checking.
2. Tighten exhaust clamps - possible they've loosened a bit - probably not related, but hearing some exhaust leakage.
3. Pull plugs & inspect to see what they indicate.
4. Re-check timing curve -- make sure full timing in by 2500-3000 & not bouncing around at higher RPM like it was earlier (I have a replacement timing light; hoping that's what it was or maybe that the problems w/intake being loose were causing that).
5. Once I've done that, what's next -- further adjusting timing or carb?
- Timing is currently at 10* initial but I've read SBF's tend to like 12-14 (Ford Racing tech also mentioned that the when i called about oil level too). Could use vacuum method of setting timing.
- Have also read missing @ cruise is likely carb related.

Anyway, i know this stuff is way easier if a methodical process is followed, just know know what that process should be. What steps should I follow?

Ok, did some checking - intake & headers hadn't loosened; they were good. Checked the advance...
idle (700rpm) 12* initial advance
1000 - 12*
1500 - 12*
2000 - 20*
2500 - 22*
3000 - 24*
3500 - 29*
4000 - 32*
4500 - 32*

Timing affect on vacuum - this doesn't seem like it could be right but it's what the gauge showed... What do you make of it?

measurements taken @ idle (although rpm increased some with advance) with air cleaner on...
12* - 6-7" vac
14* - 7-8"
18* - 8-9"
20* - 9-10
22* - 10-10.25
24* - 10-10.25
26* - 10.5-11
28* - 11
30* - 11.25-11.5
32* - 11.5
36* - 11.75
38* - 12

Also, and this also seemed too... vacuum drops when my electric fan turns on. I assume the rpm's also dropped but I didn't think to check the tack at the time. Why would that be? Fan is wired thru a relay with 10ga wire to a junction post that is fed by 10ga to the source (don't recall if I fed it from the alternator or the battery lead at the starter)

Vacuum seems very low. What cam do you have? What is your idle RPM? My 302 pulls around 18 inches at idle (900 rpm), yet the cam gives a power peak at about 5900 RPM. Often missing art cruise is due to too lean of a mixture, maybe tyou have a vacuum leak somewhere.

Cam is a B303. I think it should be way higher vacuum. Idle speed is 750. Can bump it up.

Vac readings above are with no vacuum advance (current distributor is mechanical only)

I did spray carb clean around base of carb & around intake. Engine didn't speed up any so don't think I have a vac. leak.

FWIW, I did a vac test on my 302/B303 cammed engine last week (to set idle mixture screws) and got about 16" Hg. Vac guage was "T"eed with distributor vac advance.

what are the chances my gauge isn't accurate? It's about 30 years old. Do they have a diaphragm or something in them that could dry out over time or from sitting for a long time (I probably haven't used it for 15 or so years till recently.

The vac guage I used was borrowed from a friend's retired mechanic dad - good quality but was decades old.

Maybe you are connecting the vacuum gauge to ported vacuum and not manifold vacuum.

Nope, it's on manifold vacuum (the lower of the 2 smaller ports on the carb).

That vacuum is pretty low Rob.
I would confirm it with another guage before going any further though. If it's really that low then your carb is going to be way out of wack.
Vacuum will drop some with your electric fan engagment. The alternator loads the engine and drops the rpm some causing the vac. loss.
If everything checks out ok set your timing to 38' total and we'll start setting up your carb.
Cheers
Fred

Alright. Had to go out of town twice in the past few weeks, but back now.

Intake torque was/is good.
header bolts were/are tight
swapped my MSD distributor w/o vacuum advance for a Ford Duraspark (Rich-Porter brand actually) for an 85 Mustang
swapped my plug wires (MSD cap used pin type connectors & Rich-Porter uses stock Ford cap w/regular female connectors)

Timing is now as follows (with vacuum advance disconnected & plugged at carb):
idle (~900) - 10*
1000 - 10.5*
1500 - 19.5*
2000 - 29*
2500 - 29*
3000 - 32*
3500 - 36*

And, vacuum is about 13.5 to 14" with gauge T'd into vacuum advance (connected to manifold vac).

Still have the miss when cruising at about 1800-2000 RPM.

I've read that the miss is likely a lean condition at cruise mode. Does that sound right?

One other thought since vacuum leak could also cause... I've sprayed carb cleaner all around the carb & intake gaskets - no sign of a leak. But, could having the "wrong" PCV valve be the culprit? I don't recall what application the valve I'm using is from & if it's wrong, what do I look for to get it "right"?



Edited 1 time(s). Last edit at 04/29/2012 03:04PM by rficalora.

I doubt that a PCV is contributing to your problem - It's just a dumb 'ole ball check that allows pressurized crankcase vapours into your intake manifold. A bad PCV setup would manifest itself with oil seepage/blowby at gasketted joints.
I just grabbed any old PCV off the auto parts shelf that looked the part - a 90* black elbow that would fit into my valve cover grommet..
As far as verifying a lean cruise condition, getting exhaust A/F data from a wideband O2 sensor would tell you at lot of what is going on....maybe you can get access to one!

I've thought about that Graham. Have my MSD distributor on ebay. If it sells quick I'll be able to get one. In the meantime I'm thinking of just adjusting 1 step richer for cruise mode and seeing if that helps.

on the PCV - are you saying it should be effectively closed unless there's crankcase pressure sufficient to move the ball? Mine is definitely sucking vacuum thru it all the time - hard enough I put a double layer of tape over it when I was adjusting idle mixture for max vac because I was worried it might tear a single layer. I have it connected to the large center port on the Edelbrock carb.



Edited 1 time(s). Last edit at 04/29/2012 10:11PM by rficalora.

Quote:

....are you saying it should be effectively closed unless there's crankcase pressure sufficient to move the ball?

Yes... It's a one-way check valve, so if air is flowing back thru the valve into the crankcase, it's malfunctioning.
If the PCV is removed from the valve cover (with the engine running), you should feel suction.



Edited 1 time(s). Last edit at 04/29/2012 11:10PM by ex-tyke.

Man, the numbers stamped on the metering rods are tiny. Couldn't read them even with my readers!! Should have seen me huddled over my wife's magnifying lighted makeup mirror trying to read them -- even then I could hardly make them out. Installed rods one step richer for cruise mode this morning before work. Didn't have time to try them out; will do that this evening after work.

going one stage richer on cruise mode didn't help. Still missing @ cruise. What to check next?

The good news is I don't have any fouling on the plugs any more. They are all consistent - maybe a little darker tan than I expected, but at least they're consistent color.



Edited 1 time(s). Last edit at 05/01/2012 09:36PM by rficalora.

Hmmmm. Got a PM from Kelly commenting on my cam. Called Ford to test his suggestion. Filled them in on the missing/bucking problem I'm having. Here's how the conversation went:

Ford: What RPM range?
Me: 1800-2200
Ford: That's the cam. That cam doesn't make power till 3000; what gear ratio?
Me: 3.54
Ford: Oh, yeah, you probably need 3.73; maybe 4.11

Ugh. In probably 30 seconds & in a very "matter of fact" way, they clarified what I've been working off & on to fix for a year. Granted, I've bounced around on different topics & fixed other stuff in the process, but wish I'd have known this earlier.

Net, I don't want those gears because I don't want to be revving in the 3k range cruising around. So, based on that response it sounds like I should be look to replace my cam.

Anyone disagree?

If not, suggestions for a cam to consider? Mostly street driven; no plans to drag race it; occasional autocross as in the V8 meets.

Did I say Ugh already? Oh, and thanks Kelly.

Rob,If your timing set has the 3 keyways and assuming you used straight up (advanced 4,straight up,retarded 4) you can move the power curve down 1000RPM by advancing 4 degrees, up 1000 RPM by retarding 4 degrees.

Thanks Jim. According to Ford, the B303 cam already has 4° of advance built into it. They're saying if I advanced another 4 at the timing gears it'd only move the power band about 100 rpm.

Rob, I have run a 4.56 with a 25.5 inch tire and was no where near 3000 RPM. Do you know what your OD ratio is? I have been running a 4:11 for several years now and if I recall correctly at 60 MPH I am at about 2200 RPM. A 4:11 with that cam might be an experience you don't want to pass up.