[Vindicator240]

I have an '87 5.0 with f-cam and gt40p heads, gt40 intake. Just finished it up last weekend. It runs like a champ while accelerating but at holding a steady speed or very light acceleration it jerks and misfires... I har replaced all vacuum lines and have no leaks, new plugs and wires, timing is set at 11 degrees, new fuel pump, fuel filter, new oxygen sensors. Smog pump is removed and black box under pass. Fender. I ran a scanner on it and got codes 67o, 81o, 82o, 85o, 95o. It drivin me insane! Also new pcv valve. it also idles a bit rough, bounces between 700-1000 an then holds at 900 for awhile then gets rough again... Any ideas? Btw: mass air conversion is done, mass air meter, new computer for an 89 model and wiring harness...

 

[more4u2c]

If you removed your air pump did you also remove the cat converters? If not u could have burnt up ur cats and they are clogged. They need that air pump to operate correctly.

 

[Vindicator240]

The car didn't have cats on it when I got it, and I didn't put them back on. It has ford racing shorty headers with an h pipe. Brand new o2 sensors

 

[Vindicator240]

Anyone had this trouble before? It's got me baffled and I've racked my brain

 

[Smurf stang]

I would also check for vacuum leaks around the lower intake manifold.

 

[Vindicator240]

No vacuum leaks....

 

[fast9050]

How about cleaning/replacing the EGR valve.

 

[Vindicator240]

I haven't done that yet, I've unplugged it and tried that with no difference, but I have a spare egr I could try... I'll try it and let ya know! Thanks!

 

[Vindicator240]

I changed the egr today, the old one wouldn't hold vacuum very well. An I dropped the timing from 11 degrees btc to 8 degrees. That fixed it about 95% but there's still a bit there, is that to be expected from the cam and mods?

 

[fast9050]

I changed the egr today, the old one wouldn't hold vacuum very well. An I dropped the timing from 11 degrees btc to 8 degrees. That fixed it about 95% but there's still a bit there, is that to be expected from the cam and mods?

No it shouldn't. Why the change in timing? Did she run better at 8 degrees versus 11?

 

[shaunylee]

having the same issue mate. have replaced egr with a functional unit. cleaned the MAF. no discernible vac leaks. have checked every hose. Car throws codes 33, 41, 91. Leading me to believe there is a vac leak in either the egr spacer (the gasket) or the upper to lower intake manifold.

On a side note. This is a car with gt40 heads, edelbrock intake, b cam. The edelbrock intake does NOT allow you to get the 2 bolts that are on the stock 5.0's. Right under the "5.0 HO" plate there are two long bolts that you need a huge extension for. My car is missing these two bolts. Possible vac leak here? Will let you know more.

Disconnected the MSD 6AL box and the misfire got better. Still present, but not to the degree that it was originally missing.

 

[djfaneighty8]

my 89 did the same thing for the first couple month after i bought it. I found out that the MAF was turned 180 degrees out. It wasnt getting the air flow that it should. when I rotated it, the car ran a lot better. no jerking at steady throttle and idled a lot better too. I didnt even think to do that until I was working on the car and turned the MAF a little and noticed idle improvement. maybe it is as simple as that.