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Old 03-09-2007, 07:26 PM   #1
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LT1 still starting hard and stalling...

Like the title says the LT1 is still starting hard and stalling tremendously.

Since last time I have installed a new stock fuel pressure regulator ( Aeromotive unit is a POS). I have also installed new Accel 26lbs/hr injectors and a new stock f-body LT1 MAF sensor (sent the Granetelli's MAF back).

I plan on getting a ALDL cable and running freescan or datamasters to figure out what my sensors are doing but the place I what to order from has yet to respond.

So in the meantime do you guys have anymore suggestions?

My problems are as follows:

If I let the car sit overnite and come out in the morning and start it. It starts fine with no problem. No matter if I let the car run for 30 seconds or 10 minutes if I cut it off and try to turn it back on it won't. Furthermore, If I put the car in reverse or drive and I hit the gas the car will stall or just die completely. I also hear the exhaust popping and I see alot of hydrocarbon coming from the tailpipes.

If you guys have any suggestions I would greatly appreciate it?

I have new:
Fuel Press Regulator
ICM
LT1 MAF
O2 Sensors
Injectors
NGK Plugs
MSD Wires
MSD 6AL
I have my EGR diasabled along with the AIR pump and CCP.

Thanks in advance,
Jay
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91' Z28 Vert LT1 5.7 350 & T56
Custom CAI; Accel 26lb/hr injectors
Exhaust: SLP 1-3/4 Headers & 3" Y-pipe
3" Hooker Cat-back & Aerochamber muffler.
Ported & polished intake;TPIS airfold & 160 Thermo
Ignition: MSD 6AL & MSD blaster coil & MSD Wires
Aluminum underdrive & overdrive pulley, AC delete
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Old 03-10-2007, 02:18 AM   #2
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Lets rule out the map sensor and tps sensor.

The map sensor. I think its just a 1 bar map sensor, could probably even swap one from the last engine you had in the car.

You could
A. Buy a map sensor and if its still doing the same thing then take it back to o'reillys or advance auto. Say you never used it if they even ask, and make sure you clean it up good.

B. Call up your local parts store and have them see if the map from your last engine is the same map(part number) as the LT1.

C. Check out the wiring and connector for the map, if its bad, replace that connector.

If that doesn't fix it, test the TPS sensor with a multimeter. Test the resistance(ohms). If you see any sudden changes in resistance while opening the throttle, the tps is probably bad.

Last edited by Firebat; 03-10-2007 at 02:29 AM.
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Old 03-10-2007, 02:37 AM   #3
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Firebat,

I just sold my last engine so I will have to go to auto store tomorrow and pick up a MAP sensor.

Do you think its possible I could have a bad fuel pump?

How do I actually attach the probes to test the TPS?

Thanks,
Jay
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Old 03-10-2007, 01:55 PM   #4
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Yeah it could be a fuel pump. Could be a fuel filter also. Hook up a fuel pressure gauge. While its running, if you're not seeing somewhere around 40 psi then it could be either one. If you see something like 20 psi or 10 psi, its a fuel filter or pump or even a fuel leak. You'd probably know if you have a fuel leak though. Replace the filter first. Even if you rev the engine the fuel pressure shouldn't drop that low.

TPS: Disconnect the connector on the TPS. Leave the TPS attached to the throttle body. Set the multimeter to ohms or resistance. Connect the probes to any 2 prongs on the tps until you see a resistance thats changing as you open/close the throttle body.

Last edited by Firebat; 03-10-2007 at 01:59 PM.
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Old 03-10-2007, 05:33 PM   #5
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Today, I installed a new MAP Sensor and a new Fuel Filter. The car seems to be starting better, but still with the ocassional hard start. However, the car still seems to be surging and stalling in gear. When in gear the RPM's fluctuate up and down and never to seem to settle.

Tomorrow I plan to test the TPS and Monday I will be sending the computer off to get it reprogrammed to account for the stock LT1 MAF instead of the LS1 MAF and to also account for the 26lbs/hr injectors.

Firebat, should the engine be on when testing the TPS? What is a normal rate of change I should see when opening and closing the throttle?

Thanks,
Jay
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Old 03-10-2007, 06:56 PM   #6
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Engine off. You have to take the tps connector off of the tps sensor to test it. You're just looking for a slow increase or decrease as you move the throttle. If there are any "dead spots", then bad tps.

Now your problem might just be the MAF(because the computer is programmed wrong). Unplug the MAF connector, start the car and see how it runs. It will be in speed-density mode.

The computer should be able to adjust for those injectors but not the MAF.

Last edited by Firebat; 03-10-2007 at 07:00 PM.
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Old 03-12-2007, 01:44 AM   #7
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Firebat,

I had no time to work on the car today, but thanks for all the info so far.

Jay
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Old 03-25-2007, 02:29 AM   #8
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Re: LT1 still starting hard and stalling...

Today, I got my computer back after having it reprogrammed and I also installed a new TPS.

So here's what happened...

The car started on the first try and did not want to start again after letting it run for a few minutes. So, I let it cool and everytime after that it started even if I let it run for a while. (I guess the computer just have to relearn some stuff)

Furthermore, when I went out later on it this evening it seemed like the stalling and hesitation came back alittle when I put it in gear.

I also noticed that my oil pressure was utterly low below "0 & 30". What is the stock oil pressure for an LT1?

I also noticed that I am still getting a lot hydrocarbon coming from the tailpipes.

Anyway, the only thing I can think of now is replacing the fuel pump. Which brand should I get?

If you guys(Firebat) have anymore suggestions I would greatly appreciate it.

By the way would an exhaust leak cause any of these problems?

Thanks,
Jay


New parts
Alternator
Battery
Starter
Optispark
MSD 8.5 Wires
NKG Plugs
MSD 6AL
Ignition Control Module
MAP Sensor
Throttle Position Sensor
O2 Sensors
Accel 26lbs/hr Injectors
Fuel Filter
Fuel Pres. Regulator
Oil Pressure Switch
LT1 F-body MAF
Disabled EGR, CCP & Air pump

Last edited by jagevileye21; 03-25-2007 at 02:34 AM. Reason: Added information
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Old 03-25-2007, 10:40 AM   #9
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Re: LT1 still starting hard and stalling...

First thing I would do is get rid of those Accel injectors and put some stock 24# ones back in it. Eliminate the 6AL and see how it runs. Best way to start is go back to basics like the motor was from the factory (minus the egr air pump etc etc). I have a slight exhaust leak in mine, and no problems here.

Low oil pressure on an LT1 is common with miles on it, at idle mine was just slightly above 0 and driving it was about 40-45lbs. After the rebuild with a new oil pump, it sits about the same place idle or WOT. LT1's run rich inherently, so it's gonna smoke and blow carbon out when getting on it hard.

Have you checked the FP on the car to see where it's at? And if you do need to swap the fuel pump, best one to use is the Walbro 255lph pump, can't go wrong there.
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Old 03-25-2007, 02:56 PM   #10
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Re: LT1 still starting hard and stalling...

Klortho,

I had the computer tuned by Ion @ Madz28.com to account for the 26lbs/hr injectors because my old injectors were leaking.

I will take off the MSD to see how it runs and I will have to buy a fuel pressure regulator to see what the fuel pressure is reading.

Where can I get that Walbro 255lph from and how much will it run me?

Do you think I could have a bad IAC?

Thanks for the help,
Jay

Last edited by jagevileye21; 03-26-2007 at 03:44 AM.
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Old 03-25-2007, 08:25 PM   #11
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Re: LT1 still starting hard and stalling...

I was suggesting taking the Accels off because I've heard bad things about them, but this was a couple years ago (I like to stay manufacture specific. SVO injectors in my Mustang, GM injectors in my LT1) and the fact that Accel's numbers of 26# may be different than what GM calls 26# (I know that 24# SVO injectors in a GM car is like 27-28#) It could be a bad IAC. If you know someone who has one that idle's with no problems, pull the entire TB off and bolt it to yours and see what it's doing (easier than pulling just the IAC off)

The Walbro 255 you should be able to pick it up anywhere, it's a very common pump.
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Old 03-26-2007, 12:04 AM   #12
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Re: LT1 still starting hard and stalling...

When you check your TPS use a voltmeter. You should read around .20-.90 volts with the Throttle body closed and around 4.5-5.0 volts at WOT. As stated above it should increase and decrease smoothly as you move the throttle to WOT and back. Do you have a SES light working with the LT1 in the 3rd gen? If so is it coming on? BTW what year model did your LT1 come out of?
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Old 03-26-2007, 04:01 AM   #13
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Re: LT1 still starting hard and stalling...

Klortho,

I don't have anyone close to me with a LT1 besides my dad but he is not going to take his off.

Calaban007,

I just went ahead and replaced the TPS with a new unit. I don't have a multimeter. Anyway, the LT1 is out of 95' Impala SS. The ses light is hooked up and working but not coming on. Last time I attached a scan tool it didn't show any codes.

Tomorrow, I will do the fuel pressure test and I will probably just go ahead and replace the IAC.

Does anyone know the part # for the coolant temp sensor that screws into the block?

My local auto parts stores only have the one that screws into the WP.

Last question:
How do I take off the factory oil cooler? I tried to take it off once but once it was off I had nowhere to place my oil filter. Do I need some adapter or something? I would really like to fix it because its causing me to leak a little oil.

Thanks again,
Jay
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Old 03-26-2007, 07:39 AM   #14
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Re: LT1 still starting hard and stalling...

When you take the oil cooler off, you have to put the piece that the oil filter screws onto back on the motor.
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Old 03-26-2007, 09:05 AM   #15
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Re: LT1 still starting hard and stalling...

I tore down my LT1 tonight and it has the oil cooler. The oil filter adapter remained on the block when I took the oil cooler part of it off. Looked like your standard run of the mill adapter with a couple different longer headed bolts.
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Old 03-26-2007, 11:45 PM   #16
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Re: LT1 still starting hard and stalling...

So are you guys just blocking the ports on the oil cooler and taking off the lines or are you keeping the lines on and plugging them?

Jay
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Old 03-27-2007, 03:38 AM   #17
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Re: LT1 still starting hard and stalling...

I checked the fuel pressure today and the results are as follows:

With the ignition on, & engine off - 40psi
With the engine on, & idle - 38psi
With the engine on, & hitting the accelerator to WOT - pressure moved from 38psi to 42psi

Based on these results what do you guys suggest?

Thanks,
Jay
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Old 03-27-2007, 05:31 PM   #18
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Re: LT1 still starting hard and stalling...

TPI should be between 34-47 so you're pretty much in the ballpark.

It could still be a fuel pump though.
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Old 03-28-2007, 12:31 AM   #19
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Re: LT1 still starting hard and stalling...

I tried to take it for a drive today...

But everytime I hit the accelerator the car would cut off.

I am going to change IAC Sensor as soon as the auto store gets it in stock.

I'm pretty pissed off at this point.

If you guys have any ideas let me know.

Jay
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Old 03-28-2007, 12:44 AM   #20
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Re: LT1 still starting hard and stalling...

Is there an adjustment for the TPS? If there is, you really should get yourself a multimeter to set it right.
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Old 03-28-2007, 01:00 AM   #21
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Re: LT1 still starting hard and stalling...

I wish there was some type of adjustment, but from the looks of it probably not.

I don't think that it would make sense to install the TPS any other way then with the TB blades closed.

I don't know at this point I am exhausted.


Jay
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Old 03-28-2007, 01:09 AM   #22
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Re: LT1 still starting hard and stalling...

Check this out and tell me what you think...

http://www.golenengineservice.com/html/tps.html

Jay
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Old 03-28-2007, 01:44 AM   #23
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Re: LT1 still starting hard and stalling...

You can get a Multimeter from Wal-mart for less than 20 bucks. I would highly recommend picking one up. Good Luck
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Old 03-28-2007, 01:57 AM   #24
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Re: LT1 still starting hard and stalling...

Its not that I can't afford a multimeter, I just would rather spend the money elsewhere.

I already have a multimeter its just doesn't have a very high impedance. Therefore, I'm kind of skeptical about using it.


Jay
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