Y u no run right

Rallim · Apr 28, 2014

Title says it. 94, 5.0, won't run right. Seems like it's misfiring, pretty much no power. Warrantied out distributor, tried a few different caps, two sets of wires, no vacuum leaks I can find, another set of plugs. Any ideas? Going to double check a few things when I get home tonight, see if I can see any arcing or anything at night, since I'm pretty sure it's ignition from how it sounds. Sounds the same as when I've lost a plug wire before.

RichV · Apr 28, 2014

TFI and plugs should be checked too. I take it timing is set?

Any codes? MAF, O2 sensors, and fuel pump/pressure??

Rallim · Apr 28, 2014

RichV said:
TFI and plugs should be checked too. I take it timing is set?

Any codes? MAF, O2 sensors, and fuel pump/pressure??

No relevant codes. Egr codes because its disabled, ecu storage code because I disconnect the battery since there's a draw. No difference in maf plugged in vs unplugged, that should rule that out. 02s would be in open loop at WOT and no change there so that should rule out those. Fairly sure its not the pump, walbro 255 that's had less then 2k miles on it but I'm going to pressure test it tomorrow regardless. Trying a new tfi. Second set of plugs with no change gapped at 54

86svo9l · Apr 28, 2014

Rallim said:
No difference in maf plugged in vs unplugged

Not sure about yours but mine runs like poo with the MAF unplugged. I know in the past mine has run like crap just because the MAF sensor would get dirty(K&N filters aren't all they are cracked up to be). A little sensor safe cleaning solvent and a gentle q tip cleaning would normally clear it up. I would have to do this every couple months if I drove it a lot.

If you do not have the special hex socket to get the screws out I normally just dremel a slot on the bolts so I can use a flat head screw driver.

Rallim · Apr 28, 2014

86svo9l said:
Not sure about yours but mine runs like poo with the MAF unplugged. I know in the past mine has run like crap just because the MAF sensor would get dirty(K&N filters aren't all they are cracked up to be). A little sensor safe cleaning solvent and a gentle q tip cleaning would normally clear it up. I would have to do this every couple months if I drove it a lot.

If you do not have the special hex socket to get the screws out I normally just dremel a slot on the bolts so I can use a flat head screw driver.

I do have some cleaner so doesn't hurt to try, but if it was a bad maf it would switch to a rich default map and SHOULD run better if it were shot.

toyman · Apr 28, 2014

Rallim said:
I do have some cleaner so doesn't hurt to try, but if it was a bad maf it would switch to a rich default map and SHOULD run better if it were shot.

No difference in maf plugged in vs unplugged, that should rule that out.

Your assumption is flawed. A dirty MAF may still work but the ECU reads the signal incorrectly. The MAF signal may indicate more air not necessarily less. This with the AIT and O2 sensor signals may be causing what you describe as loss of power. Also, a bad battery to engine ground can cause all kinds of sensor signal errors.

CC'S95GT · Apr 29, 2014

How old is the coil?
There is a procedure in the haynes manual to test it.

Rallim · Apr 29, 2014

CC'S95GT said:
How old is the coil?
There is a procedure in the haynes manual to test it.

Coil's about a year old, MSD coil. I've got a spare somewhere, it was pretty weak but it ran fine on it at least. I'll try to find that.

toyman said:
Your assumption is flawed. A dirty MAF may still work but the ECU reads the signal incorrectly. The MAF signal may indicate more air not necessarily less. This with the AIT and O2 sensor signals may be causing what you describe as loss of power. Also, a bad battery to engine ground can cause all kinds of sensor signal errors.

Good point. I'll try and see if I can't try another maf to rule it out.

Trying a new ICM just for fun today as well. Will report back, thanks for the ideas so far guys.