Can't get into powerband LT1 Stumped Help!!

[Guest BiltWel]

Hey guys I need a break or some advice. I pulled my Z outside to do a burnout for the first time and she moved outside fine and all, back forward the whole works. It revs great under no load but as soon as I try and power brake it for a burnout it just acts like it has a 2 ton elephant attached to the tires it will turn them over but not very well at all starts stumbling, sputtering and trys to die, it sucs. I checked for vacume leaks, checked my vacume hookup to the distributer(thought mabey it wasn't advanceing), only thing I have not checked I can think of is fuel pressure but the holley projection pump and setup I used came off my camaro with the same LT1 setup so that should not be an issue. I moved my knock sensor to the back of the head could that be it? Any advice would be greatley appreiciated I am not too proud to listen and I am also tired of looking for the problem so Please HELP!!

[280zwitha383]

Check the parking brake....

Haha, sorry it's late

[Guest BiltWel]

LOL. Whats really funny is that I already did.lol (I was truly stumped & tired)

[DaleMX]

Sounds like fuel. Maybe a bunch of crud from the tank got knocked loose and plugged the filter up. I run 2 filters on mine because so much stuff comes from the Z tank. Eventually I'll put a new tank in it, but for now I just change filters about every 500 miles.

[Guest BiltWel]

Cant be fuel has brand new fuel cell and lines an earls pre filter a holley projection after filter and I just checked the fuel pressure this morning it is at 40 psi. What else you think? I still think it has somthing to do with timing and mabey that knock sensor relocation is causing a problem but I am not sure.

[MONGO510]

check the fuel pressure under a load. See if it will maintain 40PSI. What is exhaust system?

[Guest BiltWel]

I plan on checking fuel pressure under load that may be the problem steming from running a rubber line from the tank to the pump. I think it may be sucking the line shut when I gas it under load. If this is the case I just wonder why it does not do it when it's not under load as it revs fine then. As to your question Mongo510 on the exhaust all I have now is headers and turn downs and the O2 sensors are not installed yet but I thought these engines were in closed loop until operating tempature( I think someone told me 135degrees) and that it should not affect power to the degree that this problem is just fuel consumption and the mixture? but I had a guy who knows imports tell me that he thought that could be the problem. But he is an import guy I got a couple guys coming tommorrow we're going to check it out and see on that fuel pressure situation I may have to have a braided line from tank to pump, and were also going to run a vacume test on it. We're gonna pull that gremlin out of there and set him on fire in the front yard when we find it.

[Guest BiltWel]

OK Guys I still don't know what the problem is it is not fuel when under load my pressure goes up to 42 psi so that is eliminated. I think the vacume hose going to the distributer is only for venting purposes but the little restrictor was clogged up and I fixed that and got vacume to the distributer, without any change in the performance under load acts the same way it was acting. Soooo............ this is what I have narrowed it down to. It has to be either the ECM is not advanceing the timing and is bad, the distributer is not advancing and it is bad, or the knock sensor relocation is adversley affecting the advance of the distributer, or the lack of exhaust pressure and of not having the O2 sensors installed is adversley affecting the ECM programing. What say you guys? I have heard that these optisparks are notorius for going bad and I really think that could be the problem. Let me know what you guys think. Thanks in advance.

[Tim240z]

IMHO the optispark is blamed too often. It has become a cop-out or patsy for unsolved problems with the LT1. Before you go any further, finish the work. Trying to diagnose problems with a partially complete car is futile. Get the exhaust system finished and the O2 sensors installed. Check the wiring to all the sensors. Check the following:

The resistance of the plug wires. Use an ohm meter.

Check the coil. The FSM will have a check routing with resistance parameters

Check the coil module.

Search the forum. I had a post somewhere listing the value of a resistor to put in line for the knock sensor to desensitize it.

Do you have Bosch platinum plugs in the heads? IF so remove them, discard and get some normal Champions or Delcos.

 

Hope that helps.

Tim

[Guest BiltWel]

Man this thing runs and revs like a champ at no load there has to be either a timing advance problem or a fuel starvation problem IMO. Seeing as how these engines start and run in closed loop until operating tempature I see no reason to blame the O2 sensors so that rules out the fuel problem, right? So I am left with the timing advance being the only possible problem that I can think of. I am running Champion plugs also. Somone has had to have this same problem if it is the optispark I just wish they would post if they have.

[Guest kbconv]

I'm getting ready to do an LT1 and have few ideas, but...

 

I assume you have a non MAF engine? Plug wires correct ? I've gotten lucky finding a bad plug with a timing light. It was firing inconsistantly. I'm used to Ford's. Anyway you could try pulling some codes? I would feel better if the O2's were connected.

 

Good luck.

[Guest BiltWel]

The engine is a 95 Caprice LT1 and has a maf I swear I think the distributer is not advanceing here is a link to the first time startup.

 

http://videos.streetfire.net/video/A6E6F7F6-2224-41C9-B46F-715326940DC8.htm

 

 

It runs and revs fine when not under load and idles fine when not under load in gear but as soon as I try and lay into it in gear to do a burnout or try to take off hard it sputters and backfires and looses vacume(I can feel it in the brake pedal surging trying to stall). I just don't get it man. AHHHHHHH unless it is not getting an advance signal from the ECM somehow. I have not checked that yet, actually have not read up on how to check that it is getting any and proper signal from the ECM. Any ideas would be apreciated. Thanks

[grumpyvette]

you should be able to partly check the timing advance with a timing light

(see it advance as the rpms build)

just a few questions???

 

whats your ignition timing at 1000rpm?

 

does it advance when you reve the engine???

 

did you change the cam or timing chain?????

(did you degree the cam or just match the timing marks on the timing sets gears?)

 

have you pulled any trouble codes? what were they?

 

have you adjusted/checked the TPS is set correctly with a digital volt meter?

 

have you checked each fuel injector is functioning correctly, what do the plugs look like?

 

are you sure the plug wires are going to the correct plug locations?, yeah I know you checked,when you installed them, but do yourself a favor and pull them off and re-install each plug wire after metering for resistance!

 

whats your plug gap set at?

 

have you done a compression test?

what were the results?

 

have you adjusted the valve lash/preload ??

 

are you 100% sure your in first gear?

(how do you know???)

 

is the trans control cable CORRECTLY adjusted on the throttle body to the trans??

(how do you know???)

 

and to little EXHAUST back pressure is NOT THE CAUSE, you can rule that out for SURE!!

 

is the timing tab and the damper original an are you 100% sure that the TDC on the damper and timing tab reflect REALITY

 

you need to have BOTH diagnostic software and a basic understanding of what that softwares telling you....

 

http://www.obd2.com/scantool/scantool.htm

 

http://tradervar.zoovy.com/product/EZ-S1?META=nextag-EZ-S1

 

http://www.centuryperformance.com/vacuum.asp

 

http://www.streetrodparts.tv/700R4_hookup.htm

 

http://www.gmhightechperformance.com/tech/0310htp_optispark/

[wheelman]

It's not your opti!!!

The opti will cause problems at high RPM if it's going to cause problems or run rough at all RPMS.

 

Have you tried running it without the MAF?

I have the same engine and it won't run with the MAF plugged in and the O2 sensors disconnected. Unplug the MAF and it will go into SD (speed density) mode which is less sensitive to vacuum leaks.

I also agree with TIM, finish the exhaust, get the O2 sensors plugged in then trouble shoot it.

 

Do you have a method to log data from the PCM while it's running?

If so look at the knock counts to see if the sensor(s) is causing the timing to be pulled. My guess is it is with the open exhaust your running, those sensors are pretty sensitive.

I used the circuit Tim refered to and have no problems with the knock sensors. You might try relocating them to the set back plates instead of the back of the head(s).

 

Have the injectors been cleaned?

Have you checked the MAP sensor?

Have you tested the coil?

Have you checked all the grounds for good conductivity?

What about the positive battery lead?

 

Wheelman

[Guest BiltWel]

Wheelman your suggestion on the knock sensor makes more sense than any I have heard so far. It makes perfect sense to me that it could be picking up noise from the valve train or the exhaust causing it to retard the timing thus making it run like crap under load and seem as if it is not advancing as it should be when really it is just pulling timing out because of the noise it is picking up. Just FYI I only went back with one knock sensor could that be causing a problem? should I run both? I have no way at this time to pull codes but I may be able to borrow a scan tool to do so or mabey I will buy one. Should I invest in a scan tool or software and cable interface for my shop computer which would be best? This engine ECM should be OBD1 with an OBD2 connector right? The injectors are fine, the map sensor should be fine(need to check that), the coil is fine(although I have not checked it but this thing runs and revs too good under no load to be that), I have checked all my grounds numerous times although I did not check conductivity with a meter, as to your last question what about the positive battery lead? Do you mean the ECM Hots? (Also I am not running an EGR it is plated off could this be causing a problem?) If so they are all good. Can I disconect the knock sensor just for a quick check or will I cause major damage by doing so. My experiance with pulling codes is very limited and this seems to be a problem that can be fixed without pulling codes just yet. Get back with me on this when you can. Thanks again guys for all the assistance.

[wheelman]

Don't disconnect the knock sensor, it will cause the PCM to throw a code and go into limp home mode. Won't hurt anything but will not run at it's optimum level. You might try removing it from the head then grounding it to the chassis so it won't pick up noise and see what happens.

 

One knock sensor should be fine, both of mine connect to the same pin on the PCM.

 

Your PCM should be OBDI for everything.

 

I use a laptop and the DataMaster program. I don't have a license for it (eval version) so it only will collect data for about 30 seconds but it still helps and will pull all the codes. I also use TunerCat to adjust everything. I bought a cable that has DB9 connectors at both ends and didn't use the OBDI connector I took from the donor car. I don't know anything about the scan tools so won't comment.

 

Don't assume it's the knock sensor though, be sure to check the other things and get the exhaust put together and the 02 sensors hooked up before doing any serious trouble shooting. When you do start to trouble shoot make sure to check all the sensors and the connections to the PCM.

 

I mentioned the positive battery lead because my daughter just experienced a problem with her car that was caused by corroded battery leads. The battery connectors themselves were fine but they clamped to the cables rather than being molded in. The clamped connections were bad and caused a low voltage/current condition that would show itself when the car was under load and at start up but not at idle.

 

Wheelman

[Guest BiltWel]

Dude to late on unpluging the knock sensor and I am proud to report that IT WAS THE PROBLEM!!!!! YeEEEEEEEEEE HHHAAAAwwWWW Burnout here I come I just need to remount it into the old oil pan level sending unit hole and were in business. Just for future referance to this post TO EVERYONE DOING AN LT1 SWAP DON'T USE THE CONVENIENTLEY TAPPED HOLE IN THE BACK OF THE HEAD TO MOUNT YOUR KNOCK SENSOR OR IT WILL CAUSE TIMING RETARDATION AND POSSIBLY TEMPORARY HUMAN RETARDATION FROM TRYING TO FIGURE OUT THE PROBLEM.So on to the comment you made about the battery leads. EVERYTHING in this car is brand new or has been gone through with great attention to detail so Battery lead corrosion is out of the question here. Also I wanted to mention that the donor car was a 9C1 Police cruiser so I think that it could possibley have differn't programing as I got it I am not sure on that though. By the way man MUCH APPRIECIATION ON THE BRAIN BUSTING!!!!THAT GOES OUT TO EVERYONE. You Guys are great!! Tops in my book anytime I can help you guys out with anything just let me know.

[that240guy]

You guys are all just guessing with knock sensors, optisparks and all. Wire up an ALDL connector and get a scanner and scan the computer. If your optispark is bad, you will have high and/or low resolution codes. You can watch your timing advance on the scanner. Timing lights don't work on LT1s folks seeing how there is no timing mark or pointer. Anyway, I would start with a scan tool first.

[deja]

Congrats and thanks for debugging that for the rest of us planning this swap soon.

[Guest BiltWel]

New Info although the knock sensor helped unpluging it alone did not do the trick I did have to unplug the MAF to get it to go into Speed Density Mode to do a burnout

(Thanks WheelMan for the advise on that) Everyone is right about the O2 sensors and hooking up a scan tool to find out what is really going on, I will update after I get a scan tool to use on it.

I posted the burnout video in the Non Tech Board if anyone wants to see it. Again BIG thanks to all who helped out here. now my only problem is how to get the toasty rubber off my freshly buffed quarters without damage. But thats a much better problem to have.