fresh 3800SC / 4t65e-HD (1999 GP) in a 1987 Fier oGT. a year ago, it ran fine. NOW it starts and Idles perfect, but try to drive it, give it "a little" gas and starts Missing big time." Floor it" and it backfires throught the Throttle body and has NO Power. Has fresh fuel. shows NO CODES ! Help !
I'm no expert, but I would probably check fuel pressure first, and then look at TPS. After that MAF could be unplugged to see if that clears it up ( it will go into a backup table for airflow).
When you rev it at idle, it should jump up a bit, maybe to 51. If not, check to make sure you have good vacuum at the regulator, and it's plugged into the correct port. Check for any gas in the vacuum line at the regulator ( sign of bad regulator). Other than that, I'm probably not much help....
------------------ '87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering.
I unplugged an injector plug, ran it, of course it ran with a miss. checked for codes..... Still NO Codes ! what goes on here ??? is there another way to check if the ECM is working correctly ?
Codes could have been removed, whom programmed your PCM? Typically random misfire code is removed when you have a CAM because normal idle will set off p0301.
it was programmed "Bone Stock", with just the anti theft system removed. need "suggestions" before I start just throwing money at it with the "Parts replacement method". Thanks
like originally stated " a year ago it ran fine when parked". sensor ? a wire ? was thinking of changing the TPS first, but why blow all that money on a GUESS ?! Thanks
Check the vacuum line to the MAP sensor and the MAP sensor output with a scanner. I just went thru an issue on my 3800 with 4T65E-HD with pending faults for TPS followed by pending MAF faults. The TPS fault caused it to not shift properly and the MAF faults made it run badly. I finally traced it down to a melted vacuum tube going to the MAP sensor. Once I fixed that it runs great. Thru all of this there was never a MAP fault.
Bad MAF is my guess. That is assuming the fuel pressure is staying up there when you are applying throttle. The MAF is the #1 sensor for determining how much fuel to inject. The MAP on a 3800 is a back up to the MAP.
First pull it and make sure it isn't covered with crud or baked on oil from an over oiled foam air cleaner. The MAF wires stay hot so any oil spray that gets into it will coat the wires and that coating will insulate the wires from the changes in air flow. The result is the engine will run well at a steady state but changes in throttle position cause it to lean out.
The MAF has about 20 MILES, maybe 3 hours" running time" on it since it was replaced 1 year ago. The map has never been touched. TPS is original to the engine.
The MAF has about 20 MILES, maybe 3 hours" running time" on it since it was replaced 1 year ago. The map has never been touched. TPS is original to the engine.
Those sensors can go bad without a code, they might just be sending the wrong message. Did you try unplugging any of them and revving it by hand? If you can get it to rev with them unplugged(it will run rough) that might point to a problem. The only other issue I can think of is a completely collapsed exhaust, or possible a somewhat bad ground on the ICM?
End of the day though, first thing you should check is fuel pressure. There is a reason that was the first thing said, this points to fuel pressure/regulator over anything else.
Like I said, 47 PSI at idle, 49 when rpm's go up, and the pressure holds for about an hour after it's shut down. would a bad TPS show a code ? seems to me like it's getting more Air when the throttle is pushed, but not being compensated for the right amount of fuel, to keep up with the extra air.
Like I said, 47 PSI at idle, 49 when rpm's go up, and the pressure holds for about an hour after it's shut down. would a bad TPS show a code ? seems to me like it's getting more Air when the throttle is pushed, but not being compensated for the right amount of fuel, to keep up with the extra air.
Did you check the fuel pressure regulator? Did you try cleaning out the injectors?
Theoretically, yes the TPS throws a code, but it can give bad readings without the ECM throwing a code. If you can hook a live scanner up to it, the MAF will show you if its sending a good signal. If it sat for the winter, I would take the intake tube/hose off and do a full cleaning, checking the air filter as well. Next step, clean the MAF sensor, reinstall the TPS sensor. After this, check very thoroughly for vacuum leaks. Then, take a look at the fuel pressure regulator. Next step is to check wires, make sure everything is good and there are no bad connections(especially grounds). If all those things check out, go to a junkyard and pull some spare sensors to try(or order them off of Amazon, you can return them if they don't work).
Remember: Fuel, Air, Spark. Those are the three things you need for good combustion. Check any and all systems related to those..good luck.
[This message has been edited by Threedog (edited 07-01-2017).]
If I only" HAD a Scanner" ! I have nothing but a little hand held "code reader". is a Scanner expensive ? Then I suppose it helps to know How To Use it . LOL well, what I did not want to do, "Ordered" a TPS,, MAF and a MAP. Someone asked if " I CLEANED the injectors? Short of "sending them out", is there another way ? starts & idles fine, will travel at 30MPH fine, but as soon as the throttle is pressed.. BOG, if floored.. Small backfires from the TB. no power at all.
3.82 - Ebay - Bluetooth. You can download Torque Pro to your phone and you have most of the basic scanning needs covered. You can read and clear CEL lights.
It will a little more if you get one from the states, but it will arrive sooner.
Take out your MAF sensor and inspect it. Clean it if it has crap built up on it. MAF is the main sensor for determining fuel needs. That, injectors or fuel pressure. You already checked fuel pressure so...
[This message has been edited by phonedawgz (edited 07-02-2017).]
3.82 - Ebay - Bluetooth. You can download Torque Pro to your phone and you have most of the basic scanning needs covered. You can read and clear CEL lights.
Change plugs and inspect spark plug wires. Miss under load is usually spark related. I've had plugs that worked fine in the fall miss like crazy in the spring after being parked for 4-6 months.
------------------ 10.007 @ 135.54MPH. <-- Video Best 60' 1.42 Best mph 138.82 Billet 6262 Precision turbo, PT1001 intercooler, ST1 cam, 140lb springs, comp pushrods, HV3, stock L32 bottom end and heads.
I have multiple scan cables but use the Bluetooth with the Android usually because it has no cables. When programming a PCM however then I have to use a cabled adapter.
[This message has been edited by phonedawgz (edited 07-03-2017).]
I'm not wanting to "program", I just find out WHY it's running like crap. Hopefully this scanner can point me in the right direction. Now all I'll need to do is "understand " the "Values" that this scanner provides ! LOL
I'm not wanting to "program", I just find out WHY it's running like crap. Hopefully this scanner can point me in the right direction. Now all I'll need to do is "understand " the "Values" that this scanner provides ! LOL
@ Lou6t4gto : I have been watching this thread every day. I am having almost the exact same problem. You can check out starting at THIS POST in my build thread, as there are a lot of observations and suggestions there as well that you may try.
I think I have resorted to taking it to a local Dyno shop and see if they can figure out the problem.
Check your grounds, but especially how is your ignition module grounded? If its in the stock location pull it and check the back for corrosion or anything like that.
New TPS, runs better, but still, FULL throttle it breaks up. plugs are fine, took coils off, checked IGM for ground and any corrosion, Cleaned MAF. Still waiting on MAP, and new MAF. I think maybe I'll pull the console and check ICM module and 203 "Connections".
