Need some help here guys. Installed a 305 TPI into a Miata and am firing it up for the first time. Runs but not the best. Idles. Runs rough. Low on power. Cuts out high in the RPM band. Has only 5psi (in-hg) of vacuum at idle. If revved and let off vacuum jumps and then falls back to 5. Engine is rebuild. Balanced stock pistons, LT4 production cam, testing with 1.5 rockers though. 26lb LS1 injectors w/ 89 prom with calibrator. 145psi on ALL CYLINDERS with compression test. Did have valve lash issue when first fired off. Had to back off all rockers to get compression up.
Any ideas????
Could the rockers be too tight still? Could the 1.5 rockers be an issue with eth LT4 cam?
Need help. Did hear a large exhaust leak on passengers header too, could that effect engine performance?
Also noticed cylinder #7 does not effect motor when plug wire or injector wire pulled off. ???? Plug wire has juice. Plugs are new? Injectors are used, but are low mileage vette LS1 injectors. Third gen Bosch style.
Please reply with any info possible.
Thanks
Stephen

 

Are you sure the gauge is correct? I'd tend to think that those injectors are pretty big for a 305, but I don't know why that would make low vacuum. I think that we should have decent vacuum even if the engine wasn't running, and we just turned it over. It's only the sucking from each cylinder that produces vacuum. Obviuosly something is wrong with #7 too. When you said you heard a large exhaust leak, did you mean from the header seal, or inside from a valve. Maybe the rockers are still too tight, but I doubt it. Were the rings new or how many miles? o you remember what the vacuum was on the 305?

 

Same symptoms with me a while back, except I didn't have it happen in a Miata, lol. Basically it sounds like you have a gaping hole in a vacuum line, or you left a line out, leaving a hole in the system. Check and recheck your work. Here is a diagram that may help you out.

Vacuum Diagrams

 

Headers are custom. Not much room in a Miata bay. I know that the pass side header wasn't welded as well as it should be. Just a little anxious to try things out.
Can't seem to find a vacuum leak? Maybe a leaky intake gasket or something though? Some carb cleaner while running might help? Trying to think what could be wrong?
Rings are new(moly).
Has massive headwork- port polish,, larger intake valves, Isky springs new retainers/ keepers.
Will check, but have all vacuum lines connected, PCV and fresh air hoses in place, pretty much everything in order, just runs oddly and has low vacuum at idle. Will recheck all lines and seals in the intake though.
The 26lb injectors are too big for a stock 305 prom, but I have a recalibrator with an 89 base prom, set for 26lb injectors, Air fuel ratiometer says I am stoich to slightly rich, so am fine there.
Any thoughts on how to find out why #7 doesn't seem to be running? Has compression and spark. Know of a way to check injector? I have a noid light and checked and harness checks out OK on all 8...
As always any help is greatly appreciated!!!

 

You need to get #7b firing or otherwise you'll be chasing on tail on this.

It's likely that cylinder #7 is fuel fouled by now. If you have a puddle of fuel in #7 you'll need to dry it out first. If you have an air compressor, you can pull plug #7 and run a small hose into the plug hole, letting the air run for ten minutes or so to evaporate the fuel.

A second way is to disconnect the power wires going to your fuel pump. Now if you crank the engine over, you'll burn off the residual fuel. You could also disconnect the coil wire to simply pump all cylinders without firing. Crank in short bursts as to not burn out your starter. Keep a battery charger handy. After cranking (pumping in new air) your cylinder should be clear.

A non-firing cylinder will cause a rough running engine. Got a plug wire from any other car to throw on temporarily as an A/B test. "Doesn't run with A, runs with B, therefore A is the problem". Plugs are cheap, replace #7 next.

 

Thanks for the tips. Am going out this morning to work on it again.
Maybe it is a bad plug??? Used injectors too though so I'll swap injectors next to see if the problem follows the injector or the cylinder.
Checked the plug wire an dit seems to fire, as I can hear it clicking if I place it over a bolt etc.... But Myabe I'll go buy a new set just in case as silly stuff like that could be at fault here.
Still worried about the vacuum but I am going out now to try the old carb cleaner test and see what I can find. I traced all vacuum lines last night and all were in place, tested all acc with a vacuum pump and none leak. all check out OK.
I'll post my results when I get them done.....

 

Well Found a few plugs fouled and plug wires that are new but don't seem to be transfering the spark too well. A new set of plugs and wires made it run on all cylinders. Rechecked timing as had to rough time with it partially running due to dead cylinders, was WAY off like 20 ATDC.
So now my question is this, I have a calibrator unit from TPI PARTS on it and with that and the 89 PROM it seems that I can not get it into test mode. The SES light is always on and whether I ground the TEst and GR terminals or not it won't flash etc.. Is that the nature of the calibrators? Or do I have other issues here? I know with an AUTO 87 PROM it worked just fine and would tell me codes, would disable spark advance etc.....
So Which wire is it that I can trace and install a weather pack style connector to disable spark advance? I know some F bodies had this and others used the paperclip in teh OBD1 terminal trick? I want to set my timing with the 89 prom and calibrator in the car.
Anyone know what the timing should be set to with :
POrted heads
1.92 1.50 Valves installed
LT4 production cam
Dual free flowing exhuast. Dual catco cats. Dual Dynomax Straight through mufflers.
Any help is appreciated.

 

I don't think the initial timing needs to be any different for the work; at least for normal people like me. Thiose things will help top-end flow the most, and maybe allow less total timing in my opinion.

 

What would the normal initial timing be? All the manuals I currently have, say to "check the emissions sticker under the hood" . I obviously don't have this being in an entirely different car. I need to know what the initial "should be" and what wire it is that I am in need of finding to disable the computers advance to set the initial timing without computer interference.
Other than that I think I have things all figured out and it runs much better, just want things straight before I start moving on to hunting all the little things down.

 

For the 1990 SD setup, I'm using 6 degrees BTDC. That seems to be the standard.

 

Awesome! Thank you
Now I just need to figure out how to disable the spark advance and I'll be good to go. Still have tons of other little issues here and there but this combined with getting my fuel pressures figured out will be a huge leap forward in getting this thing on the road!