Missing lt1 power help

Still no go on finding the missing 70 hp on Dan's Camaro and I could use some suggestions...

Background: Orange CMC 2 4th gen with a ’93 speed density lt1. Car runs and sounds fine with a smooth idle. It doesn't overheat on track. It seemed like the car started to lose power progressively, maybe at Hallett, more noticeable at a DE in Houston, definitely at a DE in Cresson. Found an exhaust leak including lose/missing header bolts. Replaced the header gasket and tightened everything up. Sent it to the dyno to confirm. It blew a disappointing 194 hp in the same configuration that showed over 260 earlier this year.

Did a compression check with all cylinders at about 180 psi. Replaced the knock sensor. Connector seems fine. There are no relevant codes. Fuel pressure is fine with the vacuum line off and reacts as expected with it hooked up. Replaced the optispark, cap, rotor, and plug wires. Found missing motor mount bolts right next to knock sensor. Replaced those…

Back on the dyno, no change in hp. A wideband shows A/F at 14:1 straight across the board. Given the fuel pressure and consistent ratio, it seems like the computer is commanding a lack of fuel rather than there not being enough fuel?

Probably unrelated but I’ll throw it out there anyway: Car seems to want to kill the battery enough to keep the starter from turning over after only about a week. New battery before Hallett. Everything seems fine once you get the starter to turn over a bit…

Any suggestions on what to do next are appreciated. Dan is willing to arbitrarily throw money at low probability replacement parts to try and fix this. He doesn’t have much time to work on this and time is short before nationals. He really wants to go…


Richard P.

Is the dyno graph smooth?

I'm still trying to figure out these LT1 things myself. Could it be a lack of a good spark? How about getting the ignition control module tested? Coil? Alternator?

I had a 1500 V6 truck that died/wouldn't start. Had spark from the coil, but it was a weak yellow spark. I didn't think that it would make much of a difference. Spark is spark, should ignite the mixture, right. Well, I was wrong. Replaced the coil, ran just fine.

*edit* Now that I think about it, check the simply things. I dyno'd at 273 (unrestricted) at the beginning of the year. At TWS, I dyno'd at 202. Later discovered a plug wire had fallen off. One cyl, ~70hp difference like you're experiencing.

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Originally Posted by RichardP

Replaced the optispark, cap, rotor, and plug wires.

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checked all the plugs themselves? One bad plug would screw you.
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Originally Posted by RichardP

Car seems to want to kill the battery enough to keep the starter from turning over after only about a week. New battery before Hallett. Everything seems fine once you get the starter to turn over a bit…

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</p> </p> Some kind of ground leakage? bad coil? If fuel is good is there good +12V at the coil when it's running? Is there good voltage at the PCM when it's running?
</p> try pulling a plug wire at a time to see if it makes a difference? pull an injector plug one at a time?</p></p> I sure hope you guys make it.</p>

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Originally Posted by RichardP

It seemed like the car started to lose power progressively, maybe at Hallett, more noticeable at a DE in Houston, definitely at a DE in Cresson.

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Not sure if an updated timeline will help much, but he had plenty of power through R4 at Hallett.

New O2's?
Check to make sure each injector is working?

Since it wasn't the knock sensor, I would also lean toward maybe o2's, but I wouldn't think it would be a 70hp loss.

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Originally Posted by GlennCMC70

New O2's?
Check to make sure each injector is working?

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I'll also throw O2's out as a possible culprit. It's a common misunderstanding that the computer doesn't use O2's at WOT. While that's correct, they ARE used to select the starting fuel map and timing mode prior to WOT which throws everything off. If the computer thinks the O2's are bad it will never put you in the right maps for max power. O2s can "fail" in a number of ways - only a couple of which have corresponding SES codes.

If you have access to a digital pyrometer, try to get header temps for each cylinder. If one is noticeably out of range of the others, that'll help guide you to an injector or spark problem.

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Originally Posted by Crumpacker

R4 at Hallett.

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Dude...that video makes me nervice to watch. Great racing Sam.

R1... great battle with Jeremy. I thought you were going to move him a couple of times coming out of bus stop.
R2... WOW...great run.. TWICE. This race especially made me nervous watching.
R3...What was that racing in the grass? Looking for a short cut. ;)
R4... Too bad about the tranny, but still some good close racing.

sorry for the spelling.. couldn't edit it.

Just remembered another LT1 nugget - the coolant temp sensor in the water pump is used as a critical input for fuel & timing calculations. Both the sensor itself and the pigtail it plugs into have been known to go bad and cause issues like this.

W/ the exhaust leak it had (Dan let me hear it at MSR-C) it was likely sucking in alot of oxygen and the O2 was picking this up as a lean condition and dumping fuel. It likely dumped so much fuel the O2's are now fouled. You fixed the leak, but that didn't clean up the O2's.
That is why I asked about new O2's.
Also I think Casey is on the right track as well.

Also, single wire un-heated O2's are dirt cheap. I replace mine prior to every annual dyno cert.

Lots of good suggestions for things to try. Hopefully we will get it nailed down.

The overall curves on the dyno looked OK (i.e. didn't fall flat above 4K for example) but the entire curve was a squiggly line. It was very strange. Random misfires and such usually result in spiky lines.

All of the spark plugs looked exactly the same when we pulled them out. There was nothing to point to a single cylinder having an issue. We will keep working that idea, though.

Thanks for all the help. I'll let you know what we find...


Richard P.

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Originally Posted by Casey_SS

Just remembered another LT1 nugget - the coolant temp sensor in the water pump is used as a critical input for fuel & timing calculations. Both the sensor itself and the pigtail it plugs into have been known to go bad and cause issues like this.

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Ford's, in my experience, have the same issue. Additionally, a failed/bad/malfunctioning ACT will cause all sorts of drama. Whenever I get certain symptoms that point to a failed ECT, I'll replace the ECT and ACT, just because. They're cheap, and easy to replace.

Check plugs and plug wires (remember when you're original motor was down on power, oh so many moons ago?), and the O2's as already mentioned.

Take it to Nationals - it will mysteriously gain the missing HP back.

Richard, if you need LT1 parts you guys can come up and borrow from mine. I like Casey's idea of verifying each cylinder is working with a temp gun and of validating that water temp signal going to the PCM. I've had individual wires quit and taking them off the opti to test conductivity is a giant hassle but the temps will show that. Sounds stupid but make sure the butterflies are opening all the way and that nothing (like a big pile of dirt) is plugging the intake! :)

A bit too much on the tune up parts and actually correcting the issue resulted in us diving off the end of the CMC2 chart with three runs at 271. Ooops. I can deal with that though. Some more dyno time and a smaller restrictor should get us back in the box. Thanks to the guys at Houston Performance for squeezing us into their busy dyno schedule (all three times).

I appreciate all the helpful suggestions. A shop that Dan took it to found 7 of the 8 injectors clogged. A fresh set woke it right up. Not sure of the details on what caused that or how to prevent it in the future. The car came with a fuel cell. It has an external fuel pump with a filter before the pump and a filter after the pump. Both filters are these pimpy red anodized jobbers with replaceable elements. I have no clue what is currently in them but my research suggests that the filter before the pump should be a fine stainless steel mesh rated at 100 microns and the filter after the pump should be a paper filter rated at 10 microns. We will make sure they are fresh and proper before we head out. I’m sure we will get some spares while we are at it.

Speaking of spares, does anyone have a set of stock lt1 injectors lying around that we could throw into the trailer in case we haven’t figured out the root cause and need to do another swap at the track?

We head out Monday morning! Hope to see several of you there…

Thanks again,
Richard P.

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Originally Posted by RichardP

A bit too much on the tune up parts and actually correcting the issue resulted in us diving off the end of the CMC2 chart with three runs at 271. Ooops. I can deal with that though. Some more dyno time and a smaller restrictor should get us back in the box. Thanks to the guys at Houston Performance for squeezing us into their busy dyno schedule (all three times).

I appreciate all the helpful suggestions. A shop that Dan took it to found 7 of the 8 injectors clogged. A fresh set woke it right up. Not sure of the details on what caused that or how to prevent it in the future. The car came with a fuel cell. It has an external fuel pump with a filter before the pump and a filter after the pump. Both filters are these pimpy red anodized jobbers with replaceable elements. I have no clue what is currently in them but my research suggests that the filter before the pump should be a fine stainless steel mesh rated at 100 microns and the filter after the pump should be a paper filter rated at 10 microns. We will make sure they are fresh and proper before we head out. I’m sure we will get some spares while we are at it.

Speaking of spares, does anyone have a set of stock lt1 injectors lying around that we could throw into the trailer in case we haven’t figured out the root cause and need to do another swap at the track?

We head out Monday morning! Hope to see several of you there…

Thanks again,
Richard P.

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All I can say is that I wish you guys the best of luck. Give them hell.

I use this for a fuel filter:
http://www.summitracing.com/parts/FRM-HPG1

I have never had any issues from it. My injectors are the OEM ones in place when I got the 67,000 mile motor from the salvage yard. I've never had them cleaned. I'm at 263/309 w/ a 40mm plate in place.

Good News Richard on the found HP.

I do have a set of stock injectors, but I might have a problem getting them to you on time. Let me know if you don't find another set and we can work getting these shipped.

I also have a set of stock injectors but the same logistical challenge (I'm in Austin). Let me know if you want to figure out a shipping solution...

You're free to drop by on your way north and take them off my car as long as you put them back on your way home :)