Rough idle on fresh rebuilt motor, Im lost. - Ford Truck Enthusiasts Forums
 

Go Back   Ford Truck Enthusiasts Forums > Older, Classic & Antique Trucks > 1973 - 1979 F-100 & Larger F-Series Trucks
Log In 


1973 - 1979 F-100 & Larger F-Series Trucks Discuss the Dentsides Ford Truck

Rough idle on fresh rebuilt motor, Im lost.

Reply
 
 
 
LinkBack Thread Tools Search this Thread
  #1  
Old 06-14-2016, 07:10 PM
djc1978 djc1978 is offline
New User
 
Join Date: Sep 2015
Posts: 24
djc1978 is starting off with a positive reputation.
Rough idle on fresh rebuilt motor, Im lost.

So long story short I just got my 302 completely rebuilt and now Im trying to get the truck to run. I am by no means a mechanic and am just learning as I go but here's what's happening. I changed literally everything in the engine compartment short of wiring. New holley street avenger 2 bbl, new dist, coil, plugs, wires, ect. I also blocked off the EGR valve ( if that could make a difference) I cannot get the truck to idle smoothly and the carb wants to either backfire or fall flat on its face. I timed it to 10* BTDC and then adjusted back and forth with the dist to get the highest vacuum, however the highest it gets is about 15". Any adjustment from there makes the truck idle even worse. Any idea on where to go from here? I also have tested for exhaust leaks and found nothing. The carb was working fine before the engine was rebuilt, only about a month old at that time. Thanks for any input.
DJ
Reply With Quote
  #2  
Old 06-14-2016, 10:06 PM
4x4slik's Avatar
4x4slik 4x4slik is offline
Elder User
 
Join Date: Jan 2014
Location: Chillicothe, IA
Posts: 718
4x4slik is gaining momentum as a positive member of FTE.
Check for vacuum leaks. Also, tuning is a lot of separate adjustments. Adjust your timing to it's best performance, then adjust your carb to it's best performance, then retry timing, then retry carb, etc.
__________________
77 F250 SC 2wd 400/c6
76 F350 Dump Truck, 390/4speed
05 Trailblazer wifey DD
06 Chevy 1500 WT
Reply With Quote
  #3  
Old 06-15-2016, 12:49 AM
OldMetal's Avatar
OldMetal OldMetal is offline
Elder User
 
Join Date: Feb 2008
Location: US/Baja border
Posts: 638
OldMetal is gaining momentum as a positive member of FTE.
I would be thinking vacum leak as well...
Reply With Quote
  #4  
Old 06-15-2016, 12:57 AM
EP145's Avatar
EP145 EP145 is offline
Elder User
 
Join Date: May 2007
Location: Phoenix, AZ
Posts: 543
EP145 is starting off with a positive reputation.
Check and recheck your firing ordered, are you using HO cam or early 302 cam there is a difference in the firing order. A friend of mine had the same problem as you described and we found the guy who wired it wired like a SB chevy. Here's a good reference.

Mini Tech - Ford 302 Firing Order Reference Sheet | The H.A.M.B.
__________________
73 F100 2wd SB EFI 351w AOD
Reply With Quote
  #5  
Old 06-15-2016, 01:35 PM
benbuilder's Avatar
benbuilder benbuilder is offline
Elder User
 
Join Date: Sep 2012
Posts: 538
benbuilder is starting off with a positive reputation.
subscribed
Reply With Quote
  #6  
Old 06-15-2016, 05:05 PM
djc1978 djc1978 is offline
New User
 
Join Date: Sep 2015
Posts: 24
djc1978 is starting off with a positive reputation.
Thank you for the replies. I have checked for vacuum leaks using starter fluid with no rev ups. I know that isn't completely full proof but also with having 15" vacuum I thinks that's kinda high if I had a leak ( though like I said,I am no expert) The firing order is a sticking point with me. The motor is a 91 thunderbird which should be an HO. The shop that built it did it to the newer block, however, when I try to use the HO order I cant even get it to start but with the traditional order I can get it to start fine, just idles rough, but not necessarily like it is missing (if that makes sense). So all this is exactly why I am having the problems. It seems like everything that should work just sets me back. Thanks again for everything though and please keep the ideas coming. Hopefully ill have time this weekend to get back to it.
-DJ
Reply With Quote
  #7  
Old 06-15-2016, 07:31 PM
usuallybowtie's Avatar
usuallybowtie usuallybowtie is offline
Senior User
 
Join Date: Aug 2013
Location: Terre Haute
Posts: 244
usuallybowtie is starting off with a positive reputation.
Okay...you've checked the firing order...BUT did you make sure you checked it in counter-clockwise order?
Reply With Quote
  #8  
Old 06-15-2016, 10:40 PM
4x4slik's Avatar
4x4slik 4x4slik is offline
Elder User
 
Join Date: Jan 2014
Location: Chillicothe, IA
Posts: 718
4x4slik is gaining momentum as a positive member of FTE.
I really am just throwing this out there because I don't know for sure. But I believe your firing order is determined by the cam. If you replaced it, look it up and see if you can get the firing order. wrong firing order wouldn't necessarily miss at idle.

But again, just throwing ideas out there.
__________________
77 F250 SC 2wd 400/c6
76 F350 Dump Truck, 390/4speed
05 Trailblazer wifey DD
06 Chevy 1500 WT
Reply With Quote
  #9  
Old 06-16-2016, 07:10 AM
Filthy Beast's Avatar
Filthy Beast Filthy Beast is offline
Posting Guru
 
Join Date: Mar 2011
Location: Taxachusetts
Posts: 1,151
Filthy Beast is gaining momentum as a positive member of FTE.Filthy Beast is gaining momentum as a positive member of FTE.
Use a timing light to set the timing and a vacuum gauge using manifold vacuum to set the carb and check for malfunctions. You wouldn't use a timing light to set the carb, would you? Don't use a vacuum gauge to set the timing.

15" hg vacuum is too low - you should be reading 20 - 21" hg. Suggests a vacuum leak or you're not runnin' on all eight.

Is the vacuum at 15" hg steady or fluctuating?

You said you blocked off the EGR - With a plate over the opening or just rubber nipples? If you used just rubber nipples, it could still be pulling vacuum - depress the EGR diaphragm - if the engine sounds different you have a vac leak in the EGR.

Check the hose from the manifold to the power brake booster for cracks, leaks, etc. Also check the swivel valve on the booster for leaks. If it leaks you'd also notice low brakes.

Check all rubber nubbies you have on the carb, vac tree, etc, for brittleness and/or cracks.

Vac advance diaphragm could be shot - apply suction at the vac can nipple. If you get air without the advance arm moving, the vac advance diaphragm crapped the bed.

On the rebuild - what kind of cam did they put in?
Reply With Quote
  #10  
Old 06-16-2016, 09:04 AM
flowney's Avatar
flowney flowney is offline
Senior User
 
Join Date: Jun 2014
Location: Middle Georgia
Posts: 471
flowney is starting off with a positive reputation.
If the advice above doesn't resolve the issue, it may be necessary to take a look at the valve train. Assuming hydraulic flat tappet lifters, the builder may have applied too much preload. This could cause the symptoms you are observing.
This adjustment might best be done by the engine builder. They do stand behind their work, don't they?
__________________
Frank Lowney - recovering academic
1976 F-100 LWB RWD 360/C6
1976 F-150 LWB RWD 447/C6 (Zelda)
1990 F-350 Crew Cab 460/AOD Dually
1933 6 wheel 4 dr Chev (Ford powered)
Reply With Quote
  #11  
Old 06-16-2016, 09:51 AM
Filthy Beast's Avatar
Filthy Beast Filthy Beast is offline
Posting Guru
 
Join Date: Mar 2011
Location: Taxachusetts
Posts: 1,151
Filthy Beast is gaining momentum as a positive member of FTE.Filthy Beast is gaining momentum as a positive member of FTE.
Good call there, flowney
Reply With Quote
  #12  
Old 06-16-2016, 04:16 PM
djc1978 djc1978 is offline
New User
 
Join Date: Sep 2015
Posts: 24
djc1978 is starting off with a positive reputation.
Ok, so as for the firing order I have been waiting for the builder to send me the parts list (been busy at work and unable to stop back in and keep pestering them) so I can lookup the cam. the plug wires are ran in counter clockwise direction. I did also time it with a timing light, forgot to mention that. Its at 15* no vacuum advance hooked up. the EGR valve is blocked off with a plate and I just plugged all the vacuum barbs at the engine to rule out any leaks in the lines and it didn't change the vacuum level. I also just did a compression test and all cylinders were between 118 and 125. I know that is slightly on the low side so could that and the low vacuum be indicative of something like late valve timing? The reason I haven't went right back to the builder is they don't do over the fender work and not being a mechanic, im trying to cover my end before I go through all the trouble to pull it again and it turn out fine. Again thanks for all the input, hopefully I can get something figured out and either have it back to the builder or running by next week.
Reply With Quote
  #13  
Old 06-16-2016, 05:29 PM
krazyness krazyness is online now
Senior User
 
Join Date: Dec 2014
Location: spokane
Posts: 153
krazyness is starting off with a positive reputation.
Quote:
Originally Posted by djc1978 View Post
The reason I haven't went right back to the builder is they don't do over the fender work and not being a mechanic, im trying to cover my end before I go through all the trouble to pull it again and it turn out fine.
Sounds like you need a new mechanic. Its not like they didn't expect you to install the ****...

Edit- also, if I was a mechanic with a, "no over the fender work" policy, I would break that engine in on the bench to verify its running as its supposed to be before handing it back over to the person paying for my services.
Reply With Quote
  #14  
Old 06-16-2016, 06:39 PM
djc1978 djc1978 is offline
New User
 
Join Date: Sep 2015
Posts: 24
djc1978 is starting off with a positive reputation.
I got it figured out! I had to play around with the timing just slightly to get her to fire easy every time. once I got that I switched the plug order to the HO order and she smoothed right out. Thank you all for the suggestions, its what kept me sane trying to get this. And Krazyness I agree with the firing it on a stand, I figured that's what they would do but wasn't the case, lesson learned if I ever get anything else built, but luckily they had everything right.
Reply With Quote
  #15  
Old 06-17-2016, 06:34 AM
Blue and White Blue and White is online now
Posting Guru
 
Join Date: Nov 2011
Posts: 1,777
Blue and White is gaining momentum as a positive member of FTE.
Great you got it figured out. One thing to add that may help going forward... It would be a good idea to check the timing pointer and verify true TDC.

There was some tolerance as originally built, parts changes can add error and sometimes the damper ring slips. Finding and marking true TDC on the damper or adjusting the timing pointer with the "Positive Stop Method" will make tuneups easier and may help you get her running better.
Reply With Quote
 
 
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Help asap !! firstrider 1948 - 1956 F1, F100 & Larger F-Series Trucks 31 04-14-2016 07:06 PM
low rpm hesitation and bucking edonward Ford Inline Six, 200, 250, 4.9L / 300 19 09-29-2015 04:37 PM
starting/timing issue! HELP HELP HELP!! floater87 1961 - 1966 F-100 & Larger F-Series Trucks 9 06-20-2015 10:31 AM
69 f250 idle issue 69 f250 cmpr special 1967 - 1972 F-100 & Larger F-Series Trucks 14 11-21-2014 05:04 PM
Mallory distributor install HELP!!! URGENT hellakornhaus 1967 - 1972 F-100 & Larger F-Series Trucks 7 05-31-2006 12:38 PM


Go Back   Ford Truck Enthusiasts Forums > Older, Classic & Antique Trucks > 1973 - 1979 F-100 & Larger F-Series Trucks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump



All times are GMT -5. The time now is 04:04 PM.

 

Advertising - Terms of Use - Privacy Statement - Terms of Service - Jobs
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.

vbulletin Admin Backup