Dizzy28

My 98 gt will start just fine .. But when i do any type of acceleration it loses all lower an bogs down sometimes if i shut the car off it will run ok for a few miles untill it kicks in again itll buck ect its crazy i clean the maf new fuel filter 3 months ago new plugs 3 months ago no codes are popping up the cats are deleted its been doing this before the cats were removed .. Someone please help idk what the issue is ..

Buck Sergeant

Dizzy 28, you have done great trouble shooting.
This might be my dumbest answer yet to a problem, but have you checked your timing. Set it at "total advance" not "initial advance." I hope that is all it is.

Dizzy28

How do i set the timing

Z28KLR

There are no manual timing adjustments on these engines. Can only be done via tuning.

OP, given the driveability issues you're having I am surprised that there is no check engine light or pending trouble codes to point you in the right direction. Without a trouble code it is nearly impossible to help diagnose this over the internet. Could be.... Spark/ignition related (plugs are new, how about wires and coils though?), fuel delivery (dirty/fouled injectors, weak fuel pump), O2 or MAF sensor (bad reading does not necessarily mean bad sensor, most of the time they are just doing their job). Just a couple ideas off the top of my head anyway.

But it's hard to make any sort of educated guess on this given the lack of info on the problem. And I definitely recommend against throwing parts at it, each time hoping "this" was the one. If you have inspected everything you are capable of inspecting and it all came back good, I hate to say it but your best course of action might be to take it to a shop where they can use a (very very expensive) scantool that mere mortals like us generally don't have access to (but they do, because shops can afford to buy $8K pieces of diagnostic equipment) to review various PID's in real time and come up with a pinpoint diagnosis.

Buck Sergeant

Dizzy 28, Z28KLR is absolutely right. To give you a idea of what is entailed here is a brief rundown of setting (cam) timing on a 4.6L.
Real simple to set the timing???

Put keyway on crank at 9:00 (all pistons below the deck)

Put mark on camshafts at give or take 11:00 (will have to move them accordingly later)

Lay chains out and mark each end with fingernail polish.

Put one end of painted link on mark on crank. (will be at about 5:30 or 6:00)

Put other end of painted link on the mark on camshaft.

Done.

Buck Sergeant

In regards to cam timing. Remove cam covers, damper and front cover. Do not remove chains,chain tensioners, or guides yet. Now rotate the crankshaft so the crank keyway is at 12:00. IMPORTANT! Do not move the crankshaft again until both chains,tensioners and guides have been reinstalled and tensioners released. Now remove the chain tensioners and chains. The pistons will all be low enough in the bores with the crank in this position so you can reinstall heads and rotate the cams to set the timing without bending valves. Two ways of finding the correct links to place on the crank and cam timing marks. Look carefully and you should be able to find two darker links on each chain each 180 degs from each other. Those would be the original copper colored timing links. The best way is to lay each chain down flat on a table and pull them lengthwise so you have two parallel rows of links tight against each other. At each end you will have one link facing the opposite direction of the two rows of links. There will be an equal number of links in each row making these end links the two you want to mark with a paint pen. They will be the links that are placed on the timing marks, one on the cam gear and one on the crank gear timing mark. Install the cam timing gears and crank timing gears. Now place the driverside chain with paint marked link on the crank timing gear mark. Holding the chain move it up to the cam gear and while rotating the cam timing gear only NOT THE CRANK! align the other painted chain link up with the cam gear timing mark and place it over the timing gear and into place aligned with the cam gear timing mark. The chain should now be in place with paint marked links one on the crank gear timing mark the other on the cam gear timing mark. While holding the chain tight install the chain tensioner under the chain guide and tighten both tensioner bolts. Now perform the same operation to the passenger side chain. Now visually inspect the painted links making sure that all 4 are lined up with the timing gear marks, two on the crank timing gear and one on each cam timing gear. Now remove the chain tensioner retaining pin allowing the tensioners to extend and put pressure against the chain. Reinstall HDR wheel, front cover, etc. Remember not to move the crankshaft through out all this leaving it's keyway at 12:00 through out the entire process. This is one of those things that once you do it you and get the hang of it it's quite easy. No need for special cam locks and or anything else. Good luck.

Derf00

Yeah..I'm surprised as well you haven't gotten any codes thrown yet.

With just the info in this thread I'd say your next steps are to check fuel pressure and for leaks around the intake with some starter fluid or carb cleaner. The fuel pump probably wouldn't throw a code. The intake most likely would but, it is a 98 which weren't as hyper vigilant about things and had wider tolerances before the light would trip. I once drove for almost an hour with my MAF sensor unplugged in my 99 before the light kicked on. My 08, if I let the car simply warm up with the MAF disconnected, as soon as it's at running temp, the light kicks on.

Dizzy28

Thanks guys for the help and info. Yeah tmh i dont believe its timing its not idling rough its at a constant 750 to 800 rpms at idle ive put alot into this .. I just replaced the iac modular no luck an fuel filter .. So my question even tho my fuel pump is pumping i hear it turning on thru the gas cap. An the car runs an isnt stalling out .. Actually i got in yesterday an its driving 10 times better an has today too but it feels hesitant an there is deff a studder an lack of power while accelerating i think its the fuel pump cause everytime i start the car an than go its fine than a mile later i gotta shut it off again an restart it to be fine again so how do i know if its the pump sorry if this is jumbled or mis spelled just woke up lol