Random tach missfire/tach drops, and high RPM cylinder drop out

[shackwrrr]

Im having these issues on the van and its driving me nuts. When I start it up cold I get a lot of random cutouts that make the tach drop. Once it warms up it acts fine but still has spells of cutouts every once and a while, especially after slowing down and speeding back up. The other issue I have is if I go over about 4000-4500 rpm at WOT I start to lose power and it starts misfiring once I let off the gas it continues to misfire until I come back to an idle and wait for it to clear up. Afterwards I get a lot of cutouts like when it's warming up.

Ive done some testing at idle when I am getting random cutouts, when watching coil signal it drops out every time it cuts out. I have had 2 different HEP's in it and they both were pretty much equal. Ive watched REF voltage going to the HEP and that stays constant. Ive also tried wiggle tests of every connector and wire from the HEP to the SMEC with no changes. I have no bare wires anywhere and Ive re done the grounds at the intake, neg terminal to body, and SMEC to body.

This didn't start until I put in my +40's and 3 bar in and I socketed the SMEC that was in there at the time. I originally thought it was the Ostrich so I ditched that and put a burnt chip in and nothing changed. I recently though I was a socket problem so I put in a flashable SMEC from Rob and it still does it. The PM board is different too.


I have yet to try a scaled stock cal but its on my list, I also plan to borrow a lab scope from work and watch the HEP signals and see what they do.

[zin]

Sounds a little too consistent/predictable to be random/grounds/interference...

I'd definitely try an unmolested cal, at least as close to stock as your set-up will allow. I assume this happens with any boost level, as higher rpms and higher cylinder pressures can cause the top end miss/cut-out, but will go away with lower rpm and lower boost/cylinder pressure...

Really sounds like the program/cal is trying to do something and is stepping on something's toes in the process... What, I have no clue!

Mike

[jcronk23]

I had a similar issue a couple of years back in which it turned out to be the coil and the car was laying down >3K rpm. Worth a shot if you got another coil laying around.

[shackwrrr]

I had a similar issue a couple of years back in which it turned out to be the coil and the car was laying down >3K rpm. Worth a shot if you got another coil laying around.

I have a coil I'm going to try. I've been meaning to convert to the newer coil anyway.

[shackwrrr]

Coil didn't change it.

[ShelGame]

Stock tach or aftermarket?

The stock tach gets it's signal only from the SMEC. Power and ground come from the body side. Since you've tried different SMEC"s, different chips and it sounds like even different cals - I would say it's a wiring issue. A problem with the coil wouldn't cause the stock tach to drop. Though, an aftermarket would, since they get the signal from the coil.

When I had my van, I had a similar issue. It turned out to be the ground wire under the battery tray. It's basically impossible to see from above or below (with the splash shield on). And, it's screwed into the side rail right where it tends to rust due to battery acid/salts seeping down. Mine was completely loose - it would normally touch and ground just fine, on hard acceleration it would lose contact and cutout. Sometimes it would not be contacting making it hard to start. I finally found it and re-mounted the screw to the rad support...

[shackwrrr]

I re did both that ground and the ground from the neg battery terminal to the body. I ground the paint off and used a new screw. Though I do get some ground noise in the radio still so maybe I need to put another terminal on the wire.

Stock tach

[shackwrrr]

Stock tach or aftermarket?

The stock tach gets it's signal only from the SMEC. Power and ground come from the body side. Since you've tried different SMEC"s, different chips and it sounds like even different cals - I would say it's a wiring issue. A problem with the coil wouldn't cause the stock tach to drop. Though, an aftermarket would, since they get the signal from the coil.

When I had my van, I had a similar issue. It turned out to be the ground wire under the battery tray. It's basically impossible to see from above or below (with the splash shield on). And, it's screwed into the side rail right where it tends to rust due to battery acid/salts seeping down. Mine was completely loose - it would normally touch and ground just fine, on hard acceleration it would lose contact and cutout. Sometimes it would not be contacting making it hard to start. I finally found it and re-mounted the screw to the rad support...

I re did the ground again, I got lazy and stacked the grounds on the same screw. This time I used a Roloc disc and cleaned everything then used new self tappers for the wires. Runs a lot better now, took care of everything except the High RPM missfire. I am going to try lowering boost tomorrow and see if its something to do with running 22 psi lol. I have some nasty knock in the top end of 4th and 5th so I need to keep it under 19 or so anyway. With all the other problems solved I am hoping the high rpm miss is just spark blowout.

I have done these today before fixing the grounds and nothing helped:

New BR9ES plugs gapped to .028
New spark plug wires
Swapped stock coil back in

I am going to put the AR51's back in though because the NGK's make it Idle horrible and I get some hesitation on throttle tip in.

[shackwrrr]

Did a couple pulls today at 19 psi and it did good, little knock at the top of 5th.

It still felt weird at high rpms, from 4700 on it feels like its not doing anything and the rpms stop rising as fast. I think its just hitting the limit that the stock 1 piece can handle. Time for some upgrades.