Engine will not rev past 5500 rpm under load.

Brian Standiford · Post by **Brian Standiford** » Wed Jul 12, 2006 3:45 am

1988 corvete. 640 hp@ 6800 500 torque @ 5800. Mega squirt 1W/v2.2 and msv3.o 52lbhr injectors ,msd throttle body [1000cfm] msd probillet dist, 6al box, 50psi fuel pressure fixed,# 8 feed line # 6 returns. 36 total timing. Have run on both alpha-n and speed-d. Have tried different ignition systems. Less than .08 volts a/c out of alternator.Problem is engine will not rev past 5500 rpm uner load . Even at a steady rpm with vehichle parked engine will not go past 5500 rpm. Tach goes crazy. Have unhooked digital dash and hard wired ignition feed to battery to eliminate outside noise. Even tried stock HEI dist to no avail. Can richin mixture or lean it out. Ecm responds to fuel commands but acts as if it has a rev limiter in it. Engine was dynoed on carburetion and full msd sytem . 14 full pulls and no problems. I 'm new to mega squirt but not to fuel injection. Please help.

jsmcortina · Post by **jsmcortina** » Wed Jul 12, 2006 3:56 am

Are you spark plugs resistor or non-resistor? Some people have experienced weird behaviour due to noisy non-resistor plugs.

I had a similar experience to you although with very different ignition. I'm using the wheel decoder and after swapping in a similar engine with the same electronics, crank trigger etc.etc. it would not exceed 3000rpm.
I now believe this was due to oil fouled non-resistor plugs. This is non-conclusive, but switching back to a lessy oily engine and cleaning the plugs, all is well again.

So, I _think_ it is the non-resistor plugs interfering with the tach signal.

James

ptegler · Post by **ptegler** » Wed Jul 12, 2006 4:23 am

Where do you have the MS rev limiter settings??? type?
Just up those numbers a bit. Or perhaps your injector
sizing needs attention as your maxing out what an be
delivered.

ptegler

On Wed, 12 Jul 2006 04:45:40 -0700
"Brian Standiford" <amtinc@clearwire.net> wrote:
> 1988 corvete. 640 hp@ 6800 500 torque @ 5800. Mega
>squirt 1W/v2.2 and msv3.o 52lbhr injectors ,msd throttle
>body [1000cfm] msd probillet dist, 6al box, 50psi fuel
>pressure fixed,# 8 feed line # 6 returns. 36 total
>timing. Have run on both alpha-n and speed-d. Have tried
>different ignition systems. Less than .08 volts a/c out
>of alternator.Problem is engine will not rev past 5500
>rpm uner load . Even at a steady rpm with vehichle parked
>engine will not go past 5500 rpm. Tach goes crazy. Have
>unhooked digital dash and hard wired ignition feed to
>battery to eliminate outside noise. Even tried stock HEI
>dist to no avail. Can richin mixture or lean it out. Ecm
>responds to fuel commands but acts as if it has a rev
>limiter in it. Engine was dynoed on carburetion and full
>msd sytem . 14 full pulls and no problems. I 'm new to
>mega squirt but not to fuel injection. Please help.
> _________________________________________________________
> This post is at:
> http://www.msefi.com/viewtopic.php?p=130143#130143

Paul Tegler
ptegler@cablespeed.com
http://www.teglerizer.com
Posted by email.

Brian Standiford · Post by **Brian Standiford** » Wed Jul 12, 2006 6:19 am

The rev limit is set @ 8000 rpm but will recheck. Vevicle idles @ 1000 rpm , rechecked math on injector size and should be to large if anything. Have moved fuel pressure up and down. Have tried1.0 to1.3 on threshhold and open time,have moved all accel and deaccel enrichments. Nothing has helped. Maybe I don't know how to reset rpm limit . Please give advise.Thank you.

Mike_Robert · Post by **Mike_Robert** » Wed Jul 12, 2006 6:51 am

Could you post your msq and a log demonstrating this behavior? That would be very helpful...

-Mike

jsmcortina · Post by **jsmcortina** » Wed Jul 12, 2006 8:13 am

Brian Standiford wrote: . Even at a steady rpm with vehichle parked engine will not go past 5500 rpm. Tach goes crazy.

So at present you are running with Megasquirt controlling fuel only?

How are you getting you tach signal?

When you say the tach goes crazy - is this the in-car one or the Megatune one?

(still sounds like ignition noise to me)

James

Brian Standiford · Post by **Brian Standiford** » Thu Jul 13, 2006 2:28 am

Hello. To mike. Have not data logged events. Frankly did not think about it because I had a 5 gas, fuel pressure gauge,and lap top hooked up . I will have to put somethings back together and do some data capture. James. When the tach goes away it is both the dash unit and the mega squirt . I unhooked the factory unit to see if it changed anything. It did not. And yes I am running alpha-n which makes this vehicle seem almost tame. It surprised me how well it runs clear upto 5500.

jsmcortina · Post by **jsmcortina** » Thu Jul 13, 2006 3:04 am

Could you describe how you ignition and tachos are wired up please?

If your MSD is driven straight off the dizzy and that is feeding the tacho then it sounds like the problem is not related to the Megasquirt?

Could you confirm - are you using the Megasquirt to control spark or not?

I'm still thinking that misfire or ignition noise is causing interference and a vicious circle of problems. i.e. one misfire leads to another.

James

Brian Standiford · Post by **Brian Standiford** » Thu Jul 13, 2006 4:23 am

James. Timing is full dist mechanical. No vac advance no computer control. On the msd system tach is plugged into 6al box. On the factory HEI it plugged into dist tach port and on the Crane unit it hard wired into crane box. The crane unit is a full electronic distributor with electronic advace maps and pot adjustments for rev control. The MSD unit used a chip and I tried both with and with out chip. On the Hei unit I locked the vac adv down and used just mechanical advance. I thought I might have noise on tach signal thats why I tried several styles. I should have put a lab scope on the tach signal but I don't know what a normal signal would look like as I have no referance to what normal would be. I thought it was going lean and then rich but became convinced that it was not a fuel problem but an ignition or feed back problem . I did not build this unit but have ordered a simulator box to test ecm. In 30 years of auto repair we found most of the problems were not ecm's but power, ground, or noise. The biggest problem I have is know frame of referance as to how megasquirt reacts to things such as MSD, types of plugs, wires ect.

jsmcortina · Post by **jsmcortina** » Thu Jul 13, 2006 5:35 am

As you dash tacho is going crazy and it runs directly off the spark box I would start there. Speak to MSD etc. for help on clearing up that side.

As you have dizzy -> MSD -> tacho something has to be a problem there. Even if the Megasquirt was misfueling and causing a misfire the MSD should still pickup a correct signal from the dizzy and the dash tach should be stable.

Once you've got the dash tacho stable you should have a far better experience on the Megasquirt side of things.

James

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