ar91c4

ok I have a 91 and I just put a new 383 in it and I have a major hurdle I have not a answere to..
the car completly cuts out at 4000 rpm. it acts like a top speed limiter would.if I stay in the throttle it will continue to bog but the minute i let out its fine. it runs strong untill that point.
I have replaced the whole ignition system.it is all stock but it all new also.I put a fuel pressure gauge on it and ran it up to 4 k ..and the fuel pressure didnt fall of at all.I have fms 30 lb injectors in it and a chip from pcmforless.com..I have tried it with and without the chip and got no diffrent result at hi rpms.I pulled all the plugs and they all look good.no lean or rich sighns on them.the springs are matched to the cam so I dont think it is a valve problem..the cam was degreed in at 106...


this car is driving me nuts so if anyone has any ideas please post them..thanks

Spectre

the TPI could be a restriction?

as specially on a 383 ..

ar91c4

it should be good for 5500 I think....

chevyguy1969

iTrader: (7)

When you say "cuts out" are you talking the engine starts to sputter, stall, or and just just run out of horsepower while driving? If it's sputtering or stalling it still sounds like you have some sort of ignition demon, something might be retarding your timing. If you it is just running out of power while driving you may need to port out your TPI setip to help your 383 breath more. Keep up posted on what you discover.

ar91c4

nope it just falls on its face , when i am under the hood if i nail it to the boards I can hear a simular sound from the air intake like a carb would make if the motor was to run out of gas at wot.that is what it seems like when I drive it also.but it has to be getting fuel because I have 30s in it and the plugs are not lean looking.

Spectre

what heads & cam are on the 383 ?
compression ?

Ill bet its the TPI ...

Id get an LT1 intake for FI 383 ..

ar91c4

ok well today I changed my injectors back to 24s and it dont make a diffrence...if I easy the throttle down I can get it up to 5500 but as soon as the butterflys open all the way it boggs real bad..

hey if anyone has a intake carb and distributor I will trade them my whole tpi set up for it. the distributor has all new parts,pickup coil,modual,everything...I will post this in the parts section too.

speed88

When I installed my 383 I had a similar problem. It would run great until 3000-4000 rpm's and then it woudl start to spit and sputter and lose power. I fixed by raising my fuel pressure. I had a guage and everything installed but I just didnt have the pressure high enough. I raised the pressure from 36lbs to 42lbs..I think it was...and the problem was no more. The motor pulled and ran great through all the rpm's.

kevinc

I don't agree that a properly functioning TPI will cause this behavior.

I do agree it's very likely to be limiting power production, but it wouldn't cause bogging/stumbling...the engine would just flatten out.

You mentioned the fuel pressure didn't fall, but you didnt' say what the fuel pressure was reading. What is it?

If your symptoms got worse when you downgraded to 24# injectors, that supports a conclusion that you're delivering less fuel than the chip is calibrated for.

Most tuners assume you're at ~45psi (vac reference disconnected from regulator) and do injector flow rate calcs accordingly. What's your pressure?

gta324

I had a similar problem when I had a 383...It was sucking so much air the intake pipe just sucked together and choked the engine.......... Can you scan the car?

/N.

DAVECS1

iTrader: (2)

I have a ported TPI setup on a 383. It will work without the symptoms described by ar91C4. Wehther you can extract all the power from the 383 that is debateable, but it definetly is driveable.

My first concern would be the fact you have the cam degreed in at 106. I am not sure what you mean by this, but the actual grind should have a lobe seperation somewhere around 112 or you will have to do some out of the ordinary things to get it to work with TPI and a stock ECM.

Next I am also concered about the chip. You need to know what injectors your chip was set up to operate. It is not a good idea to swap injectors and fuel pressure without knowing what the chip is set up for.

What ECM setup are you running Speed Density (MAP Sensor) or Mas Airflow (MAF Sensor). You will have an easier time using Speed Density.

Lastly you need some sort of tool to monitor timing and your fuel map while the car is running. Otherwise you might as well be performing brain surgery in the dark. You may get lucky but chances are things are not going to work when you are done.

ar91c4

OK well guys, my fuel pressure is set running at 42 lbs...my chip was calibrated for 30 lb injectors but I stuck my 24s back in to see if a diffrence would be made.the 24s are what was in the car in the first place..I also have a real bad miss when I advance my timming but te car runs a lot stronger. the miss is at like 1000-1500 rpms and it is a all the time thing when in low gear leaving the stop light. I am going to put our snap on scanner on it tomarrow at work and see what I can come up with...the question is what are the exact things I should look for when I use it because I have not had a whole lot of experiance using it....

thanks guys for all you opinions...

oh ya the car is a speed density 91 ..and the cam is a comp cam...XR276HR ...224-230@.050 510-520 lift 110* lobe sep... 106.0 intake center line..

DAVECS1

iTrader: (2)

Now I have a better idea were your at.

Well the things you will want to look at are:

You will want to varify your car is going into closed loop, as oposed to open loop.

If it goes into closed loop the BLM should read somewhere between 120-130.

You will aslo want to check your O2 voltage or reading. The main thing you want to see there is that it is varying quickly between values. This will varify it is switching and working correctly.

This is my best guess at your problem.

1. You need to verify what the initial timing is set to in your chip. Then disconnect the bypas connection and set the timing to that setting, turn off the car and reconnect the bypass.

2. Either change the injectors back to the 30Lb set and set the fuel pressure at 42 to 45 psi with the vacuume disconnected, and at approximately 100 rpm.

3. The miss sounds like your fuel enrichment table needs to be fattened up. This is usually the case when you are running a cam with something less than a 112 Lobe seperation and alot of over lap.

ar91c4

I am at work now and at lunch I will throw the scanner on it and see what I can come up with...thanks for all the info.

gta324

post the scanner reading and we'll se what happening.....

IRACE87

Quote:

I had a similar problem when I had a 383...It was sucking so much air the intake pipe just sucked together and choked the engine.......... Can you scan the car?

Like gta324 said, I had the same problem at 4800 rpm.
Follow this link
https://www.thirdgen.org/techbb2/sho...hreadid=202458

PAT

Dan8289gta

Almost sounds like timing isnt advancing from base.

ar91c4

everything from the scanner showed fine..I had a machanic with 40 yrs of expeiriance ride along and read the scanned and everything was working fine...this car has got me running in circles...nobody can seem to find out whats wrong with it..the o2 sensor shows the car is right in between rich and lean where it should be and at wot it show rich then when you let off it goes right back in between rich and lean..the tps is working fine..iac is fine..the only thing that was off was the egr but I have it deleted ..the spark advance was jumping around from 7 to18 at idle the whole time...I am going to bypass the esc and see what happens..if you guys have any more ideas please let me know..

DAVECS1

iTrader: (2)

When you say the car was reading between rich/lean what are you using to take the measurements. If you are using a normal O2 sensor, about the best you can do is verify it is switching. The BLM values do a good job of this. A normal O2 cannot really give you an accurate picture of what your fuel mixture is. For that you would need a wideband O2 Sensor.

7-18 Initial timing with the Bypass connected is way to low. I think the lowest the ECM will go is around 16. What is the initial timing set to in your chip??

Do you have the binary file that was used to burn your chip. I can look at it and tell you what your initial settings should be according to the chip.

I am sorry about the last post and the rough grammer. I was trying to get it typed fast because my wife was calling me for dinner.

At any rate. The fuel enrichment table is equivalent to the pump shot on a carbureator. When you have a cam with more overlap and a narrow lobe seperation, on a carb you usually increase the pumpshot to help get it off the line, The enrichment tables in the chip do the same thing.

Your 4800 miss sounds like it could simply be your fuel table hitting a bad value. Basically in chip there is a table like the game Battleship. Across the bottom is the RPM values from 400-6000 and along the side are map sensor readings from 0KPA to 100KPA. 100 is wide open throttle. SO the values in the 4800 and 95KPA range just may be incorrect for your engine. And the miss will happen everytime it hits this cell. You either need to increase the value or decrease the value at that spot.

KPA is the amount of vacuume measures by the map sensor. If you can get a vacuume gauge on your car that would help alot.

IRACE87

Quote:

the spark advance was jumping around from 7 to18 at idle the whole time

This is low, but at idle it's normal to see the rpm jump around, in the code if your rpm drops below the set idle rpm the ecm will add some timing to increase the rpm and when it goes above it it will remove some.

Anyway like DAVECS1 said if you can get the binary file and have someone look at it and see if there is anything wrong.

Quote:

the o2 sensor shows the car is right in between rich and lean where it should be

Don't use the stock O2 for referance because only 0.050 mvolts on the stock sensor could represent a lot on a wide band. Its not accurate.

PAT

ar91c4

I dont have the bin file but I will try to get it...I also dont know what the base timming in the chip was set to...also the rpm does not jump around the esc jumps around..it went from 7-18..does anybody know exactly what my map sensor should read through the scanner??I know it does very but I cant recall the exact number..I am going to check that again tomarrow. also my timming is set base at 0* and if I advance it at all the car runs a lot stronger but at low rpms it misses like crazy and where i have it no it seems real boggy..I can accel to like 30 and slightly put my foot on the gas and it will bog then slowly start to pull harder.. it does this at every speed at low rpms..and again all the ignition is new..I meen all of it...

kevinc

Base timing is set to 0*? I'd make a call to the people who sold you the chip, generally most factory TPI bins are 6 or 8deg in my experience and it's unlikely a tuner would have cranked it down.

I had a very lazy throttle after an intake swap once, and found the dist had slipped during final tightening...chip was burned for 8deg initial, timing light showed 2deg, that 6deg variation made a huuuuge difference.

Maybe try bringing your dist to 6deg BTDC and re-testing?

ar91c4

I set base timming a zero because if I run it anymore advanced the car misses like crazy at low rpms..

8Mike9

Too much timing shouldn't cause it to miss,,,pretty sure you'd get knocking before you detected a miss....unless the miss you feel is the timing be pulled out?

You sure the iginition is up to snuff, do another once over on the wirings for arcing and routing.

My MT2500 shows O2 mv's, does the scanner you use also show it (not just rich/lean? I used to shoot for 900-920mv off my stock O2 at WOT...as accurate as I ever was going to get...seemd to make the butt dyno feel better.

DAVECS1

iTrader: (2)

Your Map sensor will read the load on the car as stated in my last post. The map will read from 0 Kpa to 100 Kpa. A stock car will read generally in the 20 Kpa to 30Kpa at idle. At wise open every car should read close to a 100 Kpa unless there is a severe restriction.

You need to move the timing to approximately 8 degrees initial. The car is not missing when you do that. The fuel map is way off. With the cam you have selected the vacuume at idel will be less than normal. This will put you at the wrong place in the fuel map at idle. Rich or lean I do not know. Let it idle there for a minute or two and check the plugs this will probably tell the tale.

Your cam will work there are just some adjustments that have to be made in the tables to compensate for it.

As far as an ESC, The 91 ECM doesn't actually use a seperate module like the older thirdgens. It is done from the ECM. Your timing will jump around at idle with the bypass connected. If everything is on it should jump around the 20 mark. Timing value down low will need to altered to give your car a streetable idle with the cam you have selected.

I am not trying to beat you up about your cam, It may be a good cam for the combo, the computer just does not know it yet. I have tuned 1 or 2 wild engine combos in my time. It takes a little patience and some know how.

gta324

1. Can you post the scanner results here? I think the most exp guys for TPI engines can be found here.....and some mech dont have a clue for what it takes to have a modified TPI enigne to run well..............
2. Ask pcmforless if they could send you the bin they burned?

And for the timing I should guess that it should be around 24-28 at idle (800-900rpm) with that cam depending on comp and so on....so 7-18 sound way to low......

I guess that when you raise the timing it need more fuel especially when you push the throttle. Big cams like to have more AE otherwise they doesent run good. On my car I have over 30deg at idle at 65kPa and alot of AE to make my car happy.

May look into DIY burning Proms, the basics are easy when you do take the step into DIY Proms.........

ar91c4

ok guys, how about vacume leak(s)....I found three vacume leaks and one of them so happens to be the f.p. regulator,the vacume snout is cracked at the base of it and if I spray startuing fluid on it the car will rev up.and ones of the tube from the T.B to the valve cover right where it connects to the T.b...not the pcv valve side but the crank case pressure side. and the other is under the T.b where the egr vacume went..I had it pluged but not good enough.I ordered a f.p regulator and I will take care of the other ones tomarrow.

The question is,will the vacume problem on the regulator cause the map sensor and computer to screw up?

5ltrbtr

Is it an automatic or manual? I know 700R4's are supposed to lock out overdrive at full throttle. what if yours is trying to go into overdrive and is bogging the engine. that might be why when you ease on it it work fine. i might be way off but.

eric305TPI

Also make sure it is not pulling timing on the upper end as this can cause the the power to fall way off. Also I would dump the chip and learn to make one yourself.

DAVECS1

iTrader: (2)

Well That is some good investigation work! Having a vacuume leak will throw the ECM way off. If you have been reading my previous post. It use the the vacuume measured by the MAP sensor, combined with the RPM to tell the ECM which cell to use in the fuel map. Once you fix the vacuume leaks you may be able to advance the timing back up. I would also check your setting on the TB blades and air idle control motor. Fixing the fuel regulator will also bring some things around.

Also it might help us out if you could get some vacuume readings from the engine while it is running. We probably could of found this sooner. and I could take a rough guess at were the car may be in the fuel map.

By the way, in my response to the message you sent, I did not mean to make sound like I would not help you out with the programing, it is just hard to do from long distances.

ar91c4

Tomarrow I will get those vacume readings and post them. Also Yes I have read all your posts carefully but I didnt think about any vacume leaks..
Anyway I will post again with the findings, also I requested that bin file from pcmforless...

thanks for all the help so far..I cant wait to get this thing running like it should..

ar91c4

well I checked the vacume and at 800 rpms it pulled 15 inches.also I fixed my vacume leaks.I still cant turn my timming up and the car still has a hesitation and miss problem. the setting on the iac and tb blades are fine.I had to set that idle screw up a while back to get the car to idle so they might be a little open when idling. any other ideas? how do I check my map sensor??

DAVECS1

iTrader: (2)

15 inches puts you at approximately 50 Kpa. The map sensor reads from 0-100 Kpa so that puts you at about part throttle in your fuel map. If you can get on the scanner again. You can read you Map and see if it comes close to 50Kpa. It should go higher as you floor the gas pedal.

Can you easily pull just the chip out of your car, or is it soldered into a carrier?

Aslo it my be helpful if you could post the following at 800 RPM and at 2000 RPM

Map Value
Timing
O2 Sensor reading
TPS Value
Coolant Temp

ar91c4

800 rpms 2000 rpms
timing 13-18 41
map value 57 34
tps .68 .92
coolant temp 175
iac 71
02 cross counts 5-14
fuel pump 14.0 v
mat 100
prom id 8211

ok well if I ran the car up to 2k in park the map would go down to 34 but if I floored it I would get 96..
I realy hope this will tell you something..thanks again for all the replies I have got on this post and I realy do appreciate it.and the chip I have is a piggy back.I just took my old chip out and pluged it up to the new one and installed it all.

ar91c4

ttt

gta324

You need to post data when the car dies.... logg from 2000-5000rpm, all sensors. Use ECM 852 or TTS.

zz17iroc

iTrader: (4)

One of my friends had the same problem that you are describing with 383. We called all around and TPIS said to take off the air intake duct to the TB and then do a wide open pull. And guess what? It worked, no more bogging. I guess TPIS is good for something. Your engine is sucking so much air that its calapsing the intake duct. Place a small coffee can with both ends cut off of course into the duct to prevent it from calapsing. That should solve your problem.

kevinc

This man preaches the gospel truth. I was able to partially-collapse a brand new stock bellows with my old 350 on road courses...the thing routes right over the radiator, gets nice 'n hot during a 30min session, and sure enough it was costing me power.

The way I found it was watching MAP sensor readings...as the revs would climb, suddenly the MAP sensor started dropping...99 KPa...95 KPa...87 KPa...62 KPa...etc.

I hacked up something at the track, several wide zip-ties, at various points along the rubber bellows to compress it into roughly a circle instead of an oval. That held it open fine until I could work up a heat shield and internal reinforcement.

DAVECS1

iTrader: (2)

Sorry it took so long to get back to this post. I actually posted friday, but they were doing repairs to the board. At any rate those numbers are good.

They show that the sensors and ignition are working as they should.

The MAP looks similar to other cars I have tuned with the sort of cam you have. I would bet that your chip company assumed your car would travel linear through the fuel and ignition maps. What I mean by this is that they assumed that the car would go from 0-100 KPA as the pedal was pushed. In an engine with overlap you get your most vacuume right of idle as shown by the 34 Kpa value at 2000 RPM.

So what this means is your car is using the timing and ignition maps for part throttle operation (50-60 KPA) at idle, and the idle maps (30-40 KPA) at cruise. As you can see this will cause a problem.

the 94 Kpa at wide open shows that your intake is not collapsing a great deal, although that number could be a little higher. If the intake was collapseing your MAP would not increase.

Your chip needs to be reconfigured to so the values correspond with what the car is doing. PM me and maybe we can try some stuff.

ar91c4

the air intake doesnt collapse at wot. I have tried it with and without the intake and if the car is idling ,I can move the throttle to wot position from under the hood and watch the intake and theres no collapsing.the intake makes a loud gasping sound like a carb car would if it was running out if gas at wot.

ar91c4

PM sent

zz17iroc

iTrader: (4)

Have you tried to drive your car with the intake bellow removed? Reason why I asked is because my friends car only did it when he was driving and not in park. I guess you need to place a load on the engine.

Whitels1

How is your Exhaust?

ar91c4

exhaust is 3 inch pipe off headman long tubes through flowmasters.also I have drove the car without the air duct and it didnt make any diffrence.

robsgta

Have you watched your fuel pressure at WOT ?

ar91c4

yup..its fine,doesnt drop at all.

Blown87

iTrader: (1)

So, what was the final conclusion with this problem?

Shagwell

- I know this is an older post, but .68 is high for idle TPS reading. need to reset TPS to .54 - That would also screw w/ the chips programming. It'd be reading idle MAP, but part throttle TPS...

rooster433

heard about it on CF.. he was just out of gas.. he filled up his tank and hte problems went away..

Never heard anything else though

yzinger1

man if you fix this problem please let me know what you found ,mine is doing the exact thing.if you back off the throttle at all it will rev to 5800 rpms runs like it should.good luck ,if i fix mine ill let you know what i found .later jimmy