Ford Mustang Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
511 Posts
Discussion Starter #1
Ill attach a video of it here at the end of my post. Anyways at idle it sounds like i have a miss or its not firing right. instead of a healthy thump thump thump from the lope of the cam it sounds more like a quick thumthumpthumpthump in quick repetition. It started sounding like this after i originally did the HCI on the old 302 and now has the same sound with my 347 making me think there is possibly an ignition issue? anyways im not really sure where to start so i figured i would post up and see if anyone has any suggestions by listening to it.

The vid is with my old set up (HCI 302) but it sounds the same with my new engine. All ignition parts are stock original. Dist cap/rotor have less the 1k miles on them. If needed i can take a new video today.

‪89' Foxbody mustang exhaust clip‬‏ - YouTube
 

·
Registered
Joined
·
511 Posts
Discussion Starter #2
im not sure if this will tell you anything or not but yesterday after re adjusting my valves i pulled all the plugs to check them. 1,4,7,8 were dry and had a healthy light whitish color too them while the rest were wet with fuel and dark brown/black. im not sure if this was because i had a few valves that were too tight and not allowing a full burn or what. just thought i would add that though.
 

·
Registered
Joined
·
437 Posts
if u think ur valves are still a problem a compression test and or cylinder leak down test would help diagnose that
 

·
Registered
Joined
·
511 Posts
Discussion Starter #4
my valves should be good now but i will probably do a compression test next week anyways. its been driving me nuts because it just sounds strange at idle. everything sounds and feels normal while cruising.
 

·
Registered
Joined
·
511 Posts
Discussion Starter #6
^ i was told tight valves can cause it. im thinking if some of the valves are too tight then they never fully close so on those cylinders you wouldnt be getting a complete burn. thats kind of my guess but maybe someone can chime in with better info.
 

·
Registered
Joined
·
28 Posts
^ i was told tight valves can cause it. im thinking if some of the valves are too tight then they never fully close so on those cylinders you wouldnt be getting a complete burn. thats kind of my guess but maybe someone can chime in with better info.
Assuming you have hydraulic lifters, it's the other way around as valves would not reach full open status thus offsetting correct air and fuel ratio; EEC can only do so much in this department. If valves are left too tight, the hydraulic lifter would be compressed more than normal leaving less lift towards the valve to open.
 

·
Registered
Joined
·
511 Posts
Discussion Starter #8
yes i have hydraulic lifters. what you saying makes sense. im just not sure where to start on figuring out what is causing it to run like this at idle.
 

·
Registered
Joined
·
511 Posts
Discussion Starter #9
so does anyone have any suggestions or ideas? im getting it tuned in a month or so so i want to make sure there isnt something wrong before i have it thrown on the dyno. could it be that my ecu is just all messed up from the mods?
 

·
Registered
Joined
·
10 Posts
Assuming you have hydraulic lifters, it's the other way around as valves would not reach full open status thus offsetting correct air and fuel ratio; EEC can only do so much in this department. If valves are left too tight, the hydraulic lifter would be compressed more than normal leaving less lift towards the valve to open.

Is there a way to check if my valves are adjusted correctly? If they were not adjusted right could that make it pop loud threw the carb and kill the motor? cause thats what happens when i tap the throttle but only when i tap it quickly. otherwise it runs good and revs fine as long as i dont tap it.

not tryin to jack your thread man i just really need some help! i cant even drive my car so any ideas or advice would be great, thanks.
 

·
Registered
Joined
·
28 Posts
Would need more information into what setup you have. This may sound stupid but have you checked your timing with a quality timing gun? Going back to the valve issue, take one head cover off after the engine has warmed up and adjust one rocker at a time with the engine running at idle, then the other side. Messy? Yes, but fool proof. Just loosen up each rocker slowly until you hear the ticking sound from the loose gap, then tighten slowly until it goes away, then a 1/4 to half a circle clockwise after it stops ticking and your in the ball park. If this does not solve your problem, it's not the valves. Do you have aftermarket rollers? Are they all the same ratio? (intake/exhaust).
 

·
Registered
Joined
·
511 Posts
Discussion Starter #12
timing has been checked with a matco digital light. ive considered doing a running adjust but want to find some old stock covers and cut the top off of them to cut down on the mess. is there a reason you said do one side at a time instead of pulling both covers and doing both sides at once? that would be fairly time consuming since i have to pull my upper plenum to remove the valve covers. instead of listing my engine specs heres a link to the thread when i built it.

http://www.allfordmustangs.com/forums/5-0l-talk/292924-my-347-stroker-build.html
 

·
Registered
Joined
·
28 Posts
Nice assembly pics on the short block. On the valves, take both covers off if time matters, nothing special about it, except less oil mess to deal with later. I re-read your posts to see if I had missed something, you do mention that you had the same "miss" before you did the rebuild and that the engine runs good at cruise speeds. What throws me off is the spark plug reading you state which would lead me to also check on the injector side as the plug numbers you're reading out are not intake or exhaust specific and you seem to be using the same injectors that were used on the former engine setup, also general wiring and CPU connection. Would be nice to test everything with another EEC CPU if it's available to you from a friend or someone.
 

·
Registered
Joined
·
511 Posts
Discussion Starter #14
Nice assembly pics on the short block. On the valves, take both covers off if time matters, nothing special about it, except less oil mess to deal with later. I re-read your posts to see if I had missed something, you do mention that you had the same "miss" before you did the rebuild and that the engine runs good at cruise speeds. What throws me off is the spark plug reading you state which would lead me to also check on the injector side as the plug numbers you're reading out are not intake or exhaust specific and you seem to be using the same injectors that were used on the former engine setup, also general wiring and CPU connection. Would be nice to test everything with another EEC CPU if it's available to you from a friend or someone.
The injectors and MAF have about 2500 miles on them so they are pretty new still. my neighbor has a 90' gt but he just took it to a shop for bucking problems while cruising. he might let me try his out when he gets his car back. Only thing is i never had any issues untill i first did the HCI on the original motor.. since then ive had this problem.
 

·
Registered
Joined
·
28 Posts
I ran into a bad pair of "new" injectors once, just a thought. You should also be looking at a compression test if you don't trust the valves seating. Just throwing thoughts your way. I wasn't blessed on my last engine either. I ended changing a new head gasket to cure my mystery problem after I had done every nut and bolt the "right way". You have a good list of things to check on though.
 

·
Registered
Joined
·
511 Posts
Discussion Starter #16
ive got a few things im going to do this weekend and see what results i end up with.
 
1 - 17 of 17 Posts
Top