They had it as ignition pickup in the catalog? I replaced that and it didn't fix it.. The fuel pump has been making a hissing noise every few seconds for the past few weeks and it died on my last night so I am guessing that is probably my problem lol. I ordered a new one and it should be in in the next few days. Thanks for all the help guys as usual.

 

The fuel pump didn't fix it. This dead spot in the throttle is driving me crazy. I just checked the timing to make sure and it is dead on. I have literally replaced every single electronic sensor in this truck and it is still doing the same thing. Any out of the box suggestions before i take a sludge hammer to this POS?

 

Have you checked the coolant temperature sensor? This sensor allows richer mixtures and higher idle speeds until proper engine temps are reached.

I know you have replaced all of the sensors that you have stated but have you checked the voltages at all of them? It could be a wiring problem.

We had mentioned the EGR system. Did you recheck that, preferably by blanking it off?

Have you checked the vacuum source to the MAP?

 

Coolant temperature sensor eh? No I have not even checked that one yet. I didn't know that had a sensor lol. I am still new at all this stuff so bear with me

I have not checked the voltages on any of them yet, which I am going to tomorrow. I am really starting to think it is a wiring problem. There is no vacuum leaks. I have sprayed down every single vacuum line with brake cleaner and didn't hear the engine rev up at all. I am really starting to wonder if it is a problem with the TPS. It is kind of weird that the new one would have the same dead spot as the old one. Maybe a wire is fried somewhere.

I replaced the EGR Valve a couple of months ago. I probably should take it off and check it. I'll disconnect the vacuum line and see if it does anything.

Yes, the vacuum source to the MAP is good. Just to make sure I sprayed it down with some brake cleaner to make sure there were no leaks lol.

Thanks for the suggestions SEAL I will look into all of that stuff tomorrow. It has been a long day messing with this dumb thing. I'll report my findings tomorrow.

EDIT: It seems to do it more often when the engine is warmed up. If I let it set all night and let the engine cool down completely, in the morning it wont do it till the engine is warmed all the way up. I definitely will look into that coolant temperature sensor/switch.

 

You may have noticed my second quote. "I hate parts replacement as a troubleshooting strategy." It is very expensive. Voltage/continuity checks will save a lot of money by specifically identifying bad parts from good parts, and/or faulty wiring.

There is more to the EGR system than the EGR valve. A sticking EGR may be a system brake down and not an valve problem. If the EGR is sticking open removing the vacuum line may or may not find this problem. The cheapest and best way to find an EGR system problem is to remove the EGR valve and blank off the holes in the manifold with a homemade plate temporarily to see if the problem disappears. If the problem goes away then you can figure out what in the EGR system is causing the problem.

Be aware that there are 2 coolant temperature sensors. One feeds the gauge and one feeds the computer. If you are not sure which is which you can remove the sensor wire when the truck is warm and if the gauge is unaffected you have the one for the computer. It is usually the one on the drivers side in the front of the intake but these are old trucks and you can't be sure someone didn't reverse them. The fact that it seems to happen more when the engine is warm does not make me suspect this sensor/circuit as much.

Vacuum leaks are the main source of vacuum problems but clogged vacuum ports and hoses are another and will not show up by spraying with brake cleaner or other volatiles. Make sure manifold vacuum is actually at the hose where it enters the MAP.

All of this having been said I still suspect the TPS system. The fact that it seems to happen more when the engine is warm means all troubleshooting should be done when the engine is warm.

 

I checked the TPS voltage and it is right where it is supposed to be. I disconnected the vacuum line going to the diaphragm of the EGR Valve, plugged it, and started up the truck. The dead spot in the throttle is gone. I drove it around town for about 30 minutes and all is well.

I figured the EGR valve was just caked with carbon so I take it out and cleaned it a little even though it did not need it at all. I put it back on and put the vacuum line back on, it started doing it again, disconnect it and it stops.

So is the EGR Valve shot? I just replaced that thing about 6 months ago. So I doubt it is the EGR Valve. Maybe that steel pipe that goes down to the manifold clogged a little bit? That little black circular thing that connects to the EGR valve broke? I checked the vacuum hoses and they are not clogged and it does not have a vacuum leak so that is ruled out.

So I am guessing maybe the EGR Valve is bad?

 

I doubt the EGR valve itself is the problem. I suspect it is a problem with the whatever supplies vacuum to the EGR valve. It is getting vacuum when it is not supposed to and that is putting exhaust gas into the intake when it shouldn't. Mine has a solenoid that actuates the EGR valve but I am not sure about yours. The solenoid on mine is one of three beside the throttle body on the passenger side. It could also be the back pressure transducer if your system has one. The transducer is just before the EGR valve in the vacuum line. There should not be any vacuum to the EGR valve at idle or when cold.

 

It is probably the back pressure tranducer then. It is connected to the vacuum hose just before the EGR valve. I am pretty sure that I do not have an EGR solenoid just because that EGR valve connects right on top of the manifold and there is a solid pipe that goes down into the manifold so that is the only thing else that it could be. Thanks for helping me solve this issue SEAL, I really do appreciate it. I'm going to drive it around with the vacuum hose plugged for a few days just to make sure that is the problem. I am pretty dang sure it is that transducer. Once again thank you!

EDIT: Can the transducer be cleaned out or if it is the problem does it just need to be replaced? I can't seem to find it anywhere on any auto parts stores just in case that is the problem.

 

I don't know if it is available separately. I think the transducer comes as part of the EGR valve. I know mine did.

 

I replaced the transducer and egr valve since they both came together. The truck runs great now and the issue is solved. Thank you SEAL and everyone for all the help.