still more puzzling over my miss under boost

[140cilx]

My '84 'vo still has a miss right at 3400 rpm. Please give me a list of items I can check.

The miss is not noticable in first, just a short pop in second under WOT, but in 3rd and etc, much more pronounced and an actually POW (or multiple pow's)! that shakes the exhaust and breaks window's of homes nearby.

Only does it under boost, can rev past it w/o a boost load and then go to full boost and it never misses a beat.

I've done everything I can think of as follows:

-Full Motorcraft parts replacement tune up. *except Ignition Module (it's Advance Auto - any chance this is the prob?)
-Timing set to stock.
-Unplugged the computer overnite so it can begin afresh.
-Taken the plastic cover off the VAM and cleaned the contact w/ electric parts cleaner.
-KS unplugged.
-Fuel Pump is new 190lph, fuel filter is new.
-20 lbs boost, which it can hit around 3k, handles the boost fine before and after this 3.4k miss.

I'm going to put in a LA3 and brown tops, but am now hoping to fix this beforehand.

What else should I check? I'm at a loss.

I even replaced the heater core and it didn't help.

Thanks mucho!

edit: oh yeah, and the intake, vam, throttle body are as dry and clean as a bone, no blow by, new late model valve seals, burns no oil. Plugs read healthy.

[SVOJEFF]

This may be off the wall! Check the hoses to throttle body from intercooler lines? You still have yours front mount right? Also check the plug ends to your vain meter? Mine were broke where you could not see them and it was doing the same thing! Hope you can find it soon? Just my 2 cents worth!

[140cilx]

thanks guys.

I just did a bunch of search and read's per Mikes reply and I'll just for giggles try some octane boost. I've been running 93 octane forever from a couple of different locations that sell a lot of gas and seem reputable. Both are Texaco.

btw it does it in either position of the octane switch, and doesn't do it after the 3.4k, just that one spot. Ton's of torque before and after that spot. Thus I was leaning toward an electric glitch somewhere, like a sensor. I also thought bad injector, but why would it stick consistently at one rpm and be fine from there?

- from the post's I read, one scenario is having a leaking injector (which I do have), but the part that confuses me is the specific rpm. I used to get some pooling in the lower intake, for some reason that stopped. But anyway, after that rpm it's fine and just pulls like a freak.

I've even done the steam cleaning technique (in the past) where you clean up the head a bit of carbon deposit's by sucking water into the vacuum lines. Blow's it out of the exhaust as steam. Seems to be as clean as can be hoped.

Jeff, thanks, I'll def check those tonite.

accepting input here!

[NY eric]

would

A bad TPS cause something like this from happening.? like a dead spot. Since you say it is at the same point 3,4k I am thinking that a volltmeter and a few min you could prove that.

Just a thought.

[GAboySVO]

140cilx,

Pat_in_LA and I recently worked on his friends '84 that had a very similar symptom. It turned out that he had a shot O2 sensor and weak plug wires and plugs although he thought he had recently replaced them.

Have you run the codes since the reset? Checked the plug condition? Try regapping the plugs to 0.30.

[140cilx]

OK, I'll run codes, actually haven't done that.

O2 sensor only has about 7k on it, but who knows - I'll do that last as those are expensive. And the plugs and wires were replaced when this problem surfaced. Probably only have 200 miles on them since.

Plugs are gapped to .32, but heck, I'll try it.

Thanks for the good input, Eric, I'll check the TPS tonite as well. Can't hurt.

I'm at the point where I'm willing to check anything.

[Pro-Hawk]

I was wondering if you figured out what was wrong with your car yet? My car seems to be doing the same thing even though I've done a full MotorCraft tune-up and replaced the O2 sensor. I think I got a Leaky injector but not sure this is whats causeing my cars missing once I'm in the boost. I did back fire a few times when I let off the gas at around 2-3k and it messed up my VAM. They tell me my back fire is most likely because of a leaky injector since the car was gitting fuel to backfire after I let off the gas. So I figured I would check with you and see if you fixed yours and how.

Thanks

[140cilx]

it turns out Rich suggested I check my cam timing - and it's off a tooth. So I def have a possible solution to my problem. Somehow it skipped a tooth.

On a sidenote I had already ordered an adjustable cam gear and I did get it over the weekend, but haven't touched the car yet. I'll def let you know. I was finishing up my other car this weekend.

[Pro-Hawk]

Originally posted by 140cilx
it turns out Rich suggested I check my cam timing - and it's off a tooth. So I def have a possible solution to my problem. Somehow it skipped a tooth.

On a sidenote I had already ordered an adjustable cam gear and I did get it over the weekend, but haven't touched the car yet. I'll def let you know. I was finishing up my other car this weekend.

My car acts like your car but I'm not sure its the Cam timing either. I set the timming to 11 degrees I believe and checked my belt. Now my belt is in good shape buts its going to be replaced anyways since I just got the car. I want a freash start on knowing how old everything is and that its working right

[turbizzy]

TPS?

140, just wondering if you checked your TPS with an ANALOG (needle type, not digital) voltmeter yet? This test will for sure tell you if your TPS is bad, best test. Just watch the needle sweep as you manually open the throttleblade by hand and watch for a smooth needle sweep with no interuptions such as a sudden stop or even needle drops. I say this becuz my 85 did the SAME EXACT THING, replaced TPS after verifiying dead spot at 1/2 throttle, good afterwards.

Definately run codes to see if EEC is picking this up. On the puddling fuel issue, this happened to me when i swapped in my 35ers, i removed the upper intake and pushed in the injectors along with the rail into the intake firmly enough to bend in the rail at the mounts a bit, this solved the leaky #1 injector, wasn't seated all the way.

[140cilx]

I will do those things, replace timing belt, check w/ analog voltmeter (Dad's got one), etc.

EVERY moment I've had the last few weeks has been on the LX turbo conversion car.

I might be able to do it this weekend. I will report once I've got it fixed.

Then I'm tossing in the browntops, LA3, ACT sensor. I want my 'vo as smooth as the LX.

Thanks for the continued help.

[Eyelawdoc]

Before you start changing out everything on the SVO, I suggest you find and fix the cause of your problem. Pay particular attention to the condition of your wiriing to the TFI and TPS. I've seen quite a few 84's with wiring problems in these areas. Trying to fix them by changing out components without first verifying that the wiring is in primo condition is like chasing a ghost.

Have you tried pulling codes recently? They can help point you in the right direction! Forget about trying to do it with an analog voltmeter and buy yourself a code reader. It's one of the best $20 you'll ever spend!

[SVOJEFF]

Ghost chasing!

Yeh i just did some of that just yesterday with my 85 wiring! i found a wire on the back of the motor in that clump of wires that goes to the firewall under the black shield broke and hanging like my sons tooth! I fixed it now i can boost up to 16 and up on the factory guage, were before it would fall and pop and miss so I would have to let off of it to catch it self up and then change the gears. The wire was the orange and white. But yes check all your wireing one that you might have missed will make all the world of difference! I am getting my SVO ready for the 40th show! I am going to drive it down there with my son which is 7 and knows everything about cars and Mustangs! I am trying to figure the mileage I will get with my SVO? My guage looks right but sometimes I go to fill up and it doesn't take but 11.6 gals to fill it up when it is the right side of the E. I can get 265 miles when it gets to that point.

[140cilx]

the latest updates. Indeed timing belt had jumped a tooth.

replaced the timing belt, added a Ford Motorsport gear so I could set the cam to the recommended 4 degree's retard to maximize the torque curve.

-this did not solve the problem.



Swapped computers, put in an LA series, Act Sensor and Browntops. Nice improvement! Wow!

-this did not solve the problem.



-so, as soon as I have some chores around the house completed I'm going to put the TPS on the old needle style voltmeter and hope and pray it has a dead spot. I've got a few spares I will swap in either way.

I'm gonna add some grounds to the wiring harness under the hood. My LX really liked it when I did this, maybe the 'vo will, we'll see.

ANY OTHER IDEAS OF WHAT MIGHT BE CAUSING THE MISS? (Miss is understatement - when under boost it bangs, bucks, ka-pows) then pulls hard and strong above that rpm. When not in boost, it pulls through it w/ zero problem, smooth as can be.

It could be in the wiring, and if it is, it'll be sheer luck if I find it, NOT my strongpoint. Although I have the wiring clean and looking good, someone did a real hackjob on it at some point.

[SVOeric]

here are a few thoughts -- more like ramblings, but here ya go

CHECK THAT TPS --

Have you tried to check the fuel pressure while the car is under load ? (IE: Pressure gauge taped to the windshield)

hook up a timing light, and you should be seeing 20+ degrees of advance (with the spout connected)

Make sure plugging, and unplugging the spout makes a difference in timing. (not a good idea to hot-swap while the car is running)

My other thought involves the PIP ?? Do you know if it has ever been replaced ? -- do you know what color it is ??

This would be a good time to check the codes -- (I know it has been mentioned several times)

Here is another question for you -- is the car running like gangbusters, and the falls on it's face, or is it like it is slowly accelerating, and spitting and sputtering ????