im at my wits end with my 89 k2500 need some help.

[topumpchump]

I have a 1989 k2500 5.7 tbi with 171,xxx miles on it. I've had no issues with it until a month ago when the engine is under load it cuts out, as soon as I let off it back fires and everything is normal. I've replaced cap and rotor, plugs and wires, coil, egr valve and solenoid, map sensor, tps and fuel filter trying to track down the culprit. Ran the codes, it came back with code 34 map sensor. Unsure why, cleared the codes and it throws it again. The truck idles just fine just won't drive well.

 

I should probably also include that the truck has no cat anymore and is 3" straight pipped back to a flowmaster. Unsure if that will make any difference with help as it had had this set up for over a year prior to any issues. Please help, I'm not used to these tbi systems but more familiar with old school engines that only need suck, blow, bang to run correct.

[Chris]

Suck, squeeze, bang, blow

 

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[txab]

Checked fuel pressure and flow?

[Jsdirt]

And in that order, too.

 

 

The pump, regulator (or both), or the MAP sensor could be failing. Check the fuel pressure first. If that checks out ok, look in the intake while it's running & make sure the spray pattern looks good. If it's dumping fuel in there, or starving it, the vacuum line to the MAP might be busted, or the MAP itself is junk.

[topumpchump]

I've been told by some that its the pump starting to fail. I've got one from AC delco. The injectors seem to be spraying just fine. No dribbling or anything. I've also heard that with the way the truck is acting that a pressure test may not be reliable, it runs like a raped ape at idle, its the driving part that it can't comprehend.

[topumpchump]

If anything its running rich. Its definitely not starved at all

[topumpchump]

So I just picked up fuel pump today. Gotta wait till this weekend to drop the tank and put it in. It also came with the pig tails for the harness apparently no one but GM includes these anymore. Hopefully this will fix the issue. If y'all have any other ideas that might help. They'd be greatly appreciated.

[bossier62guy]

My dad's 89 had exactly the same problem.....pulled the bed off, pulled the fuel pump out of the tank, a short piece of rubber hose that was part of the pump assy had deteriorated and had a slit in it. We replaced that short rubber hose and it fixed the problem. That was about 2 years ago. BTW, his was a 1500 series but an HD model w/ the 5.7.

[topumpchump]

I'll be replacing that this weekend and that hose did come with the new one. I'll be sure to examine it all before it goes back in the tank.

[topumpchump]

Well its been raining like no tomorrow here. I did go ahead and replace the pressure regulator to rule that out. Looks like fuel pump it must be. I'll update this as soon as I get the chance to do the pump.

[topumpchump]

So the pump got replaced just now, also changed the regulator and still no change. Please help before I lose my mind.

 

So the pump got replaced just now, also changed the regulator and still no change. Please help before I lose my mind.

[bossier62guy]

Sorry to hear that but i'm assuming you never checked the fuel pressure before you changed that pump out....i'd definitely check it now.

[topumpchump]

Well considering the fuel delivery system is now new that rules that out. Right like I said used to working on old mechanical engines.

[bossier62guy]

I personally don't take those things for granted but it is your truck. Hopefully someone else can suggest another troubleshooting path. Good luck with it.

[citydriver]

Put a vacuum gauge on it. Best bet is to check the vacuum readings at the MAP sensor ( rectangular unit with a vacuum hose a 3 wire connector ) usually mounted to a bracket on the passenger side of the engine, to the rear. You should have approximately 18 - 21 in. @ idle depending on the age and condition of the engine. Higher is better. The base idle should be around 600 rpm. The ECM uses that sensor to calculate the fuel/air mixture, in conjunction with the Throttle Position Sensor (TPS) and the O2 sensor (if it's still there after the cat was pulled) So if it's giving you a 34 code, there is a reason for it. Start with a visual and check ALL of the vacuum lines, making sure they are connected and in good condition. The base plate of the TBI (throttle body) may have excessive carbon build up restricting or blocking the vacuum ports. But if there is vacuum at the MAP, it's probably not blocked. That's where I would start........ If everything else checks out, change the MAP sensor around $40-70 depending where you purchase it from.