lt4 hot cam install troubleshooting
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Teching In
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lt4 hot cam install troubleshooting Help!! Car struggles to idle when first starting and falls on its face as if fuel starved but no codes
Here's the backround info: every sensor is new and Delco with proper voltage reference and reading properly via multi meter, snap on verus and Matco maximus scanner. No codes, no ses, no po300, no knock or misfires in the current or history counts, o2's are Delco and read/flux as they should, all new Delco injectors, opti, coil, icm, plugs(gapped as per hcc instructions and pcm tuner) wires, fp regulator, pump, and filter, Holds steady 15psi vac at idle and fp 45psi at the rail increasing with revs never going below 40psi, (opening relief valve does not stall the motor) no vac leaks, no exhaust leaks, short term and long term fuel trims +/- 1or 2, and 13.25v of batt when running.
Mods done:
1997 lt1 with Complete Lt4 hot cam kit, 1.6rr and springs, extreme duty timing, long tubes, no cats, slp cai, loudmouth, the egr, a.i.r., asr have been deleted, has a Soloman tune, all parts installed by professionals as per GM spec or as listed in the kits instructions...
What the heck am I missing??
Here's the backround info: every sensor is new and Delco with proper voltage reference and reading properly via multi meter, snap on verus and Matco maximus scanner. No codes, no ses, no po300, no knock or misfires in the current or history counts, o2's are Delco and read/flux as they should, all new Delco injectors, opti, coil, icm, plugs(gapped as per hcc instructions and pcm tuner) wires, fp regulator, pump, and filter, Holds steady 15psi vac at idle and fp 45psi at the rail increasing with revs never going below 40psi, (opening relief valve does not stall the motor) no vac leaks, no exhaust leaks, short term and long term fuel trims +/- 1or 2, and 13.25v of batt when running.
Mods done:
1997 lt1 with Complete Lt4 hot cam kit, 1.6rr and springs, extreme duty timing, long tubes, no cats, slp cai, loudmouth, the egr, a.i.r., asr have been deleted, has a Soloman tune, all parts installed by professionals as per GM spec or as listed in the kits instructions...
What the heck am I missing??
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did you unplug the battery or pull the pcm fuse for 20 minutes to reset the fuel trims first? If so and it won't run in speed density, AND all your sensors are giving the proper readouts, then maybe your tune is off, specifically the VE table. I have no experience with Solomon but it's possible he uploaded a tune for a huge cam by accident, he's human after all. The fact that all your fuel trims are right on the money yet the car still doesn't like it is a red flag for me. Sounds like you should have ran the car long enough for the PCM to at least learn idle. If I've cut power to my PCM and it has to relearn everything, it will have trouble transitioning from throttle back to idle for a few minutes but that's it. Unless... did you specifically tell Solomon to run your car in closed loop with MAF only? In that case he might've left the VE table alone which would help explain the stalling in speed density.
also, you say you have 15psi vacuum at idle. is that supposed to be your MAP reading? I'm used to seeing map in kPa and a quick internet search says a LT4 Hotcam should be at 45-50kpa at idle (6.5-7.5 psi). I'll wait to hear if MAP is what you were talking about before going down that rabbit hole.
also, you say you have 15psi vacuum at idle. is that supposed to be your MAP reading? I'm used to seeing map in kPa and a quick internet search says a LT4 Hotcam should be at 45-50kpa at idle (6.5-7.5 psi). I'll wait to hear if MAP is what you were talking about before going down that rabbit hole.
Thread Starter
Teching In
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I asked Soloman for a hot cam tune and to remove asr, egr, rear o2s, vats and a.i.r. , i did not request anything other than what he reccomended as per his experience, I heard lots of good things about his work so i left it in his hands. Im thinking i might try a stock pcm to see if the problem resolves,( i know it will run super rich and idle low but it should eliminate the pcm as the problem if the stumble resolves.
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From: Milton, PA
Check your valve lash again... I just installed an LT4 GM Performance Hot Cam Kit on my 93 and after days of Diag I popped the valve covers off and readjusted the valves and she started right up.
Teching In
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From: Long Island
I just installed a LT4 hot cam in my 94 z28 along with supporting mods and had Soloman tune it same as you. I did have an issue with the new 26lb injectors I installed initially. They would get stuck open and had a poor spray pattern. The engine was hard to start, idled poorly and would run rich. I put the old stock injectors back in and it ran fine.
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Update**
Thanks for all your suggestions so far y'all, i had a couple other minor issues that have been solved and I have ruled out pcm, opti, coil, icm, maf, and map sensors. I have now narrowed the issue down to a lean condition on bank 1, (the fuel trims show 20% positive enrichment, and are in the single digits on bank 2) so I marked and switched all injectors from one side to the other and problem remained the same on bank 1, I have practially soaked the intake in carb cleaner to try to find a leak but so far nothing, im going to try switching the o2's to see if it switches banks, if no change im thinking of checking/ replacing the header gasket on bank 1(although i hear no leak). After that I cant think of anything else that would only affect one bank, I have checked the valves and they are adjusted properly. Any more suggestions?
Thanks for all your suggestions so far y'all, i had a couple other minor issues that have been solved and I have ruled out pcm, opti, coil, icm, maf, and map sensors. I have now narrowed the issue down to a lean condition on bank 1, (the fuel trims show 20% positive enrichment, and are in the single digits on bank 2) so I marked and switched all injectors from one side to the other and problem remained the same on bank 1, I have practially soaked the intake in carb cleaner to try to find a leak but so far nothing, im going to try switching the o2's to see if it switches banks, if no change im thinking of checking/ replacing the header gasket on bank 1(although i hear no leak). After that I cant think of anything else that would only affect one bank, I have checked the valves and they are adjusted properly. Any more suggestions?
I'm going back to the tune. I dealt with split trims for a long time and it wasn't until I started tuning myself that I noticed the farther out from stoic the car was, the more split the trims were. No idea why. Once I got the trims closer to 14.7, the closer the banks were to each other. (unfortunately the car drives better a little rich so my trims are about 8-10% split again.)
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Update no.2***
Car now starts, stays running, and is now driveable, the only issues left are hesitation till aboit 2500-3000rpm, and surging idle commanded is 800 and it will dip as low as 650 then surge to 950 then rest at 800-850 for about 5-10 sec then surge again, (I know its not the lope theres a noticable difference) problem is worse when hot, and running longer, then it needs spoon feeding at lights to keep from stalling. I have replaced, reset and adjusted the iac valve problem remains.
Car now starts, stays running, and is now driveable, the only issues left are hesitation till aboit 2500-3000rpm, and surging idle commanded is 800 and it will dip as low as 650 then surge to 950 then rest at 800-850 for about 5-10 sec then surge again, (I know its not the lope theres a noticable difference) problem is worse when hot, and running longer, then it needs spoon feeding at lights to keep from stalling. I have replaced, reset and adjusted the iac valve problem remains.