1997 Hardbody no power on acceleration

[Cornbinder57]

I thought the negative number meant the ECU is leaning out the mixture because the signals the ecu is receiving is saying the mixture is too rich? Am I understanding you to say that the negative number means the mixture is to lean? And it needs more fuel? Sorry don’t want to be dumb just my first time working on a rig newer than 1957.

[Cornbinder57]

Update:
Took it for a test around the block. Still no power in the 2200-2900 rpm range at 3000 it takes off up to 4 k. No power on hills. With the exhaust pipe hanging on the bolts from manifold 1/2” gap, manifold is still cherry red.

Long term fuel trim: -1.6 at idle and 0 at driving
Map 9.9 in Hg at idle and solid 28hg at driving past 50% throttle. (Baro in my area is 28.8)

MAF reading 2 lbs at idle 4.1-5 in acceleration

Up stream O2 .6 down stream .01-.13 while driving

Fuel pressure 36 psi idle and 46 psi accelerating (actual road numbers)

I’m at a loss, going to check all vacuum lines today and re check electrical connections.

Any other insight would be greatly appreciated.

[PaulC]

Have you double checked the timing? Maybe try another timing light. It seems that may be the most likely culprit at this point. Late timing can cause all the symptoms you're having.

[Deerhurst]

You've confirmed the manifold is clear, right?



-1.6 is lean but not by much. 2lbs/s at idle sounds crazy high. My 3.0V6 Audi pulls 4-5g/s at idle and ~170g/s at WOT.



Unless you mean g/s then it sounds quite low which would say either bad MAF or vacuum leak to me though that should cause you to run rich due to unmetered air. I'd expect 3-4g/s at idle for a 2.4L.



Your O2 readings tell me lean too. I want to say I usually see closer to 1.0 under accel.



My D21 pulls ~23inHG of vacuum at idle and around 10inHG at cruising load. You should see low manifold pressure (lots of vacuum) at idle and the pressure differential will fall to 0.

[Cornbinder57]

Thank you all for input and help.

Culprit has been found…bad fuel pressure regulator. The pressure was reading fine, however the return was wide open, had as much flow in as out. Which caused lack of pressure within the injectors. Changed out the fuel pressure regulator, checked and cleaned spark plugs, and she runs like a champ now. Idles smooth and accelerated through the curve just fine and will hold hills in 4th gear. Manifold temp had gone down as well, no more cherry glow.

Thank you again for all the help and ideas.

[USCGamecocks20]

Originally Posted by Cornbinder57

Thank you all for input and help.

Culprit has been found…bad fuel pressure regulator. The pressure was reading fine, however the return was wide open, had as much flow in as out. Which caused lack of pressure within the injectors. Changed out the fuel pressure regulator, checked and cleaned spark plugs, and she runs like a champ now. Idles smooth and accelerated through the curve just fine and will hold hills in 4th gear. Manifold temp had gone down as well, no more cherry glow.

Thank you again for all the help and ideas.

That is awesome news….congrats man! Thanks for the update.

It’s irrelevant now that the issue is resolved, but per my understanding of the FPR, it appears to have been working correctly for maintaining the pressure in your injectors. The “full flow” through the return line is normal, as long as you’re maintaining the correct PSI ahead of the regulator, the rest of the fuel bypasses the regulator and goes back to the tank (so there will always be a constant flow through the return line with the truck running and pump on).

For example your pump may produce 80 total PSI, and at idle 36 PSI is kept under pressure behind the regulator, but the remainder is allowed to “bypass” the regulator and go back to the tank.

You also saw an increase in PSI (roughly the right amount) when you pulled the vacuum line on your FPR, which tells you that the regulator wasn’t stuck shut or open, and appeared to be maintaining roughly the correct pressures with/without vacuum.

The FPR can fail in other ways, like a broken diaphragm that allows gasoline to get sucked through the vacuum line and back through the intake, which may have been happening.

Either way though, the FPR had to have been causing your issues, so congrats again on tracking it down and getting it resolved! Has to be an awesome feeling not having the truck about to melt after a short drive haha.