upper rpm misfire
11-01-2013, 12:15 AM
#1
Thread Starter
Join Date: Jul 2013
Location: NC
Posts: 19
upper rpm misfire
Hey guys I have a 88 5.0 and it has the normal ad-ons ie: aluminum heads,cam, both intakes trickflow & and c.a.i.....I'm having a problem with what feels like a engine skip/misfire but it's seemingly only in the upper rpm range anywhere above 3500. If I hold out a gear or if I step on it and the rpms get above that range that's when I notice it most. Low range and highway speeds seem ok other than an occasional cut off when I go in on the clutch. I suspect a vaccuum leak somewhere and have looked around for one many times to no success but still not ruling that out. Overall it seems to run too good to be anything major but Any ideas on this problem from you all would be appreciated.
I have replaced the coil recently with no change. Could it be vaccum leak, timing off, or possibly even the fuel psi which is currently at 33psi
I have replaced the coil recently with no change. Could it be vaccum leak, timing off, or possibly even the fuel psi which is currently at 33psi
11-01-2013, 07:27 AM
#3
6th Gear Member
Join Date: Mar 2010
Location: Wisconsin
Posts: 5,061
Fuel pressure is alittle low, but I don't know your whole setup, and I don't think that would cause a miss. But with your mods I would bump it up alittle, maybe 38lbs to start.
How's the obvious stuff, plugs, wires, cap? Whenever I get a misfire, that's where I start.
How's the obvious stuff, plugs, wires, cap? Whenever I get a misfire, that's where I start.
11-02-2013, 11:12 AM
#4
Thread Starter
Join Date: Jul 2013
Location: NC
Posts: 19
I was gonna change my rotor button but can't get it off lol, there is a little corrosion on my distributor cap, wires and plugs are fairly new. What gap would you recommend on the plugs was gonna recheck those. Will bump the fuel psi and try that, gonna let u know when I do
Fuel pressure is alittle low, but I don't know your whole setup, and I don't think that would cause a miss. But with your mods I would bump it up alittle, maybe 38lbs to start.
How's the obvious stuff, plugs, wires, cap? Whenever I get a misfire, that's where I start.
How's the obvious stuff, plugs, wires, cap? Whenever I get a misfire, that's where I start.
11-02-2013, 11:18 AM
#5
Thread Starter
Join Date: Jul 2013
Location: NC
Posts: 19
That's all the more reason for me to put the msd distributor that a friend is giving me in. Gotta get a msd box, the only reason its not in yet lol. I'm cleaning my corroded distributor cap now and gonna pull a few plugs to check. Will let you know my findings
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11-04-2013, 02:49 PM
#6
2nd Gear Member
Join Date: Jun 2011
Location: Ohio
Posts: 166
When I bought my GT (2yrs ago) it was doing the same thing. Turned out to be a dirty MAF. You might try some of the special spray cleaner that doesn't leave a residue.
Last edited by wydopnthrtl; 11-04-2013 at 02:58 PM.
11-04-2013, 03:25 PM
#7
2nd Gear Member
Join Date: Jul 2006
Location: Louisiana
Posts: 315
Msd dis is junk do not toss it on there
I would tell u to replace the plugs and clean the maf sensor, you issues will probably be gone then
fuel pressure should be 33ish at idle, that would give u 40psi base, however if you have anything less than 30lb injectors you will have to kick the fuel pressure up to 55psi and you really should consider getting a chip at that point
give this a good read, it'll give u a bunch of excellent knowledge
www.efidynotuning.com/ford/pre.htm
I would tell u to replace the plugs and clean the maf sensor, you issues will probably be gone then
fuel pressure should be 33ish at idle, that would give u 40psi base, however if you have anything less than 30lb injectors you will have to kick the fuel pressure up to 55psi and you really should consider getting a chip at that point
give this a good read, it'll give u a bunch of excellent knowledge
www.efidynotuning.com/ford/pre.htm
11-06-2013, 09:18 PM
#8
Thread Starter
Join Date: Jul 2013
Location: NC
Posts: 19
I did do a random check on my plugs, I didn't do all of them but I did check 4 of them checking 2 on each side. They all looked pretty good. I didn't think to look at my maf but I have cleaned it about 2 months ago. I bumped up my fuel pressure to 38 lbs, cleaned my distributor cap contacts and it seemed to clear up but i think it stil has a miss in there every now and then... It definately is better than it was tho. Cant say what the fix was with doing them both at the same time. Honestly I think it still has a vaccum leak somewhere
Msd dis is junk do not toss it on there
I would tell u to replace the plugs and clean the maf sensor, you issues will probably be gone then
fuel pressure should be 33ish at idle, that would give u 40psi base, however if you have anything less than 30lb injectors you will have to kick the fuel pressure up to 55psi and you really should consider getting a chip at that point
give this a good read, it'll give u a bunch of excellent knowledge
www.efidynotuning.com/ford/pre.htm
I would tell u to replace the plugs and clean the maf sensor, you issues will probably be gone then
fuel pressure should be 33ish at idle, that would give u 40psi base, however if you have anything less than 30lb injectors you will have to kick the fuel pressure up to 55psi and you really should consider getting a chip at that point
give this a good read, it'll give u a bunch of excellent knowledge
www.efidynotuning.com/ford/pre.htm
11-12-2013, 12:31 PM
#10
Join Date: Sep 2003
Location: United States
Posts: 26
Dirty Mass Air Flow from K&N filter oil
[QUOTE=wydopnthrtl;8304941]When I bought my GT (2yrs ago) it was doing the same thing. Turned out to be a dirty MAF. You might try some of the special spray cleaner that doesn't leave a residue.
Completely agree with the advice to use the correct cleaner for MAF. I cleaned and oiled my K&N filter (in stock position). The previous owner had a Cold Air Intake (CAI) which I removed. I chased the 'miss' starting at 3500 rpm (that is where the ECU changes timing) for months: new fuel filter, new plugs, 9mm plug wires, checked fuel pressure was in spec, new cap and rotor. Finally cleaning the MAF allowed all the other maintenance to have a chance to work. Scared me the first time the tach took off above 3500 rpm. Now I use the cleaner every few months to be sure no K&N element oil has covered the heated MAF wire. No more issues.
Completely agree with the advice to use the correct cleaner for MAF. I cleaned and oiled my K&N filter (in stock position). The previous owner had a Cold Air Intake (CAI) which I removed. I chased the 'miss' starting at 3500 rpm (that is where the ECU changes timing) for months: new fuel filter, new plugs, 9mm plug wires, checked fuel pressure was in spec, new cap and rotor. Finally cleaning the MAF allowed all the other maintenance to have a chance to work. Scared me the first time the tach took off above 3500 rpm. Now I use the cleaner every few months to be sure no K&N element oil has covered the heated MAF wire. No more issues.