DM91RS

Just installed Vortec heads, Performer Vortec intake and Crane 1.6 rollers.

I have tried different PSI's, injectors(stock and 55lb's), timing and tinkered with the prom. I do not know enough about tuning to determine what the problem(s) are.

It runs like it misses at times, runs ok at times, chugs at times, backfires at times, lags when given throttle and if the throttle is used heavy, lags and then takes off well with no knock counts. The eng cranks right up.

Which injectors would be better? The stock with more pressure or the 55's which I cannot seem to turn down below 12psi for some reason?

Thanks for any help! This is my daily ride and it's getting on my last nerve. LOL

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91 RS 5.0 TBI...Vortec heads...Edel Performer Intake...LT4 cam...1.6 Crane golds...TES headers...3"Dynomax exhaust...5spd... 3.08...Ultimate tbi...afpr...ZR 255-50's...Koni's

killer305

iTrader: (1)

its like im looking in a fing mirror i am having the EXact same problems, man i thouhgt it was just me

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90 RS 305 tbi, 4 3/4" cowl Hood, Edelbrock TES headers, Flowmaster exhaust, Crane roller cam, comp roller rockers, vortec heads/intake, ported tbi, w/new injectors, MSD probillet Distributer/ coil, 1 inch tbi spacer, air foil, 14x4 k&n flat base air cleaner, Rebuilt 700r4 w/ B&M shift kit, B&M Megashifter, 3.23 posi, 2 12 RF's with mtx amp, top of line alpine cd player,autometer phantom gauges, soon to have 91-92 gfx, z-28 wing, new paintjob, rims, all new suspension, and new inteior

Brent

iTrader: (1)

What do the BLM's look like during idle, and different speeds in 4th and 5th gear?

What vacuum or MAP does it idle at? Should be 18-20" or 30-40KPA.

What have you changed in your prom?

DM91RS

BLM's at idle look decent, sometimes even settling around 128. On the x-way between the way traffic has been screwed up this week and the thing running so rough I have not been able to get real good readings but some of those have not looked that bad at around 120. On the ride in this morning the engine was so jerky that I finally had to go down from 5th to 4th and leave it there.

The vac at idle is around 18. I checked for vac leaks yesterday as it was running that rough but I found none.

I have tried changing the BPW and moved the fuel tables around a bit but I have not really gotten any good results yet.

I did a plug check and it was clean and white like it was not too rich. When it cranks up cold the idle smells really rich.

I had the timing (base) set at 6 and then 4 and now 2 (which runs the worst).

I still have the 55lb injectors installed.

Brent

iTrader: (1)

Since the BLM is close to 128 I would set the intial timing to stock (zero). Then I would add timing in the cruise areas (main spark table) in 2-3 degreee increments and see how it responds. Keep your eye on the plugs and knock counts. Be patient and you'll get there.

Make one change at a time so you don't get confused as to what worked.

I'd say the cold start rich smell is ok. My stock TBI truck smells too. Warmed up you shouldn't have any smell. The wet flow mainfold needs the extra fuel because cold mainfolds don't keep fuel suspended in the air stream so well.

Pablo

iTrader: (1)

not enough timing

my car did it too, and the more base i gave it the better it ran.

My suggestion to you is to use that table that fast broker posted awhile back which is essentially a copy of a mechanical advance setup with a vac. advance can.. i beleive they were specs for some hp parts. Set your base timing at 6 at the dist and in the chip, eliminate WOT timing addition, and just make all your changes in the main table. With the vortecs Id start off with a total WOT timing of around 32 degrees in by 2800 rpm
then fine tune it

Pablo

iTrader: (1)

to clarify, 6 in the chip so in the main table the idle timing area is around 20 degrees or so give or take.. thats about what mine likes yours will probably be good with less I imagine

DM91RS

Thanks for the replys guys!

After going back and looking at the bins I realized that I was not starting with the stock bin. So I reburnt the stock bin and it is much more drivable now.

I think that it does need more pump shot because it really hesitates and spits back through the intake (sounds like) and watching the map voltage it jumps up and the eng seems to fall flat on its face.

It cranks well, idles well and when hot after both 30 minute drives today the BLM's are at 127-128 with 1.37-1.41 map volts at 750 rpm.

No knock counts at all even with several heavy (WOT) runs through a couple of gears including 4th. Under WOT it sounds good but, as I said it really hesitates before "catching up and going". It also seems to need to catch up when under certain cruise conditions when applying throttle any way but as you had an egg under your foot.

I will start trying different timing settings now.

One question to make sure in Tunercat when you raise the BPW does this increase or decrease the fuel?

Thanks again!

DM91RS

Would not trying different BPW's be the same as changing the fuel pressure? I cannot tell any fine adjustment to the fuel pressure with the guage that I have and I thought that varying the psi would be more precise.

Thanks for any replys.

Brent

iTrader: (1)

Yes is the short answer. You want to balance the BPW with FP and the VE tables. They all affect each other.

If you set the BPW too low for a given FP you won't have enough WOT fuel because the VE1 & 2 added together can't equal more than 100.

I personally would leave the BPW stock and compensate with FP and the VE tables. I'd start with a FP that is high enough to support your estimated HP then work on the VE tables. If you don't have enough FP you will be lean at WOT no matter what the BPW and VE is set at.

If you raise the BPW too much you could end up running the injectors at 100% duty cycle which is not good.

DM91RS

Thanks Brent

I probably should leave the BPW and the PSI as they are because WOT seems to do well. No spark knocks but need to do some plug cuts.

Working on the VE tables should probably be #1 on my list after trying different base timing settings.

The main problem still is hesitation when given throttle.

Later

Pablo

iTrader: (1)

the hesitation when you hit the throttle is because the engine needs more pump shot.
Either rig up your aircleaner so that there is more restriction above the throttle blades, like a ring extending up from the base till about an inch from the lid or adjust your TPS pump shot (what I would do provided you are in fact running an aircleaner)
Look at other TBI chips (small block chips) and find one with more TPS pump shot and just copy the table.. you might have to test out a few

Pablo

iTrader: (1)

btw the other symptoms.. the hesitation at cruise, that sounds like it needs more timing

un4givin89

i've got a 305 LO3, plan on doing same mods, what product parts did you use?

JPrevost

I had the same problem with my 350 vortec motor and it turned out to be the fuel filter. It went bad in only 6K miles. My BLMs all looked normal but when I would drive and give it a blip of the throttle it would fall on it's face. It got so bad that when I would press down on the throttle it would backfire though the intake and almost shut down. $15 and it fixed my problem. Another way to check if it's your fuel filter is to flip the tps sensor and watch the fuel. There should be a LOT of fuel coming out of BOTH injectors and the car should stall or come very very very close.
It really sounds like you're running lean when you snap open the throttle. Try and make all your BLMs around 124 and see if the hesitation gets worse or goes away.
Good luck

DM91RS

Hey guys! I'm still tuning and if you've checked the board you will see my other post about unstable fuel pressure and that's what I'm fighting now. I've been guessing that it's the pump but not really looking forward to doing one over the holidays.

Pablo I have upped the PS vs TPS several times and it has helped but I think that for now the varying fuel pressure is kicking my butt trying to get a handle on things. I do know after two days of lower (10 compared to 12) psi that it runs better at the lower pressure.

I will take your advice and add some timing at cruise after I get the BLM's where they need to be. Right now they are above 130 at a steady cruise and from what JP and Grumpy has said they need to be on the slightly lower side of 128 ie: 124-126. Correct me if I'm wrong on this.

JP the thing runs so well at full throttle I don't think that the fuel filter has a problem and I changed it about 5 months ago.

Right now I need to get the fuel pressure steady.

Thanks for the replys.

DM91RS

I'm not sure what you're asking but just let me know and I'll be glad to give you a complete list with part numbers if that's what you want.

Later