Engine/Transmission (1998.5 - 2002) Hesitation between 1000-1900rpm

[kingdutch]

Hello,



I have hesitation between idle and 1900 or so rpm.

The test is when I am dead stopped and then floor it. The truck moves forward (slowly) and then gradually builds speed until the engine rpms get to around 1900. . then the truck takes off.



I doubt it is the new Goerend Bros transmission and t/c I just had installed (it did this prior to the new transmission). I did the APPS reset thing, no change.



I have read in other posts that this might be because of a bad boost sensor (is that the same as the IAT sensor?)? I do not currently have a fuel pressure gauge on, but that will be getting fixed next week when it arrives in the mail.



What else can I do to troubleshoot this?



Thanks!

 

[nps]

king,



Your sig says you have an HO with an auto - did you do a conversion? HOs only came from the factory with a 6 speed.



My stock HO would be 'sluggish' up to about 1900 RPMs then take off like a raped ape - caused by the stock fueling coming on. Putting an EZ on it cured that problem - now it runs hard off idle.



Borrow an EZ from someone and try it out. I can't say how my HO would have felt behind an auto - with the stick you only experienced the lag briefly when first starting out.

 

[RustyJC]

As mentioned, the stock fueling curve for the ETH increased fueling rates very slowly below (in my truck's case) 2100 RPM, then the truck would take off. This was done to keep increases in boost ahead of increases in fuel to minimize smoke. This disappeared with the installation of the EZ.



Rusty

 

[kingdutch]

Very interesting... Thanks for the info.

I have read that others have had similar problems to mine, and the replacement of an IAT, MAPS, APPS, and even a VP44 fixed their hesitation problems.

I really need to get this fuel pressure gauge on. . waiting. .



I did not do a conversion, but I could have sworn that original window sticker said the engine was an HO. I could be wrong. Is there a way to tell?



Thanks...

 

[RustyJC]

If the truck came with a 47RE automatic, it's an SO (option code ETC). The HO (option code ETH) only came with the NV5600 6-speed manual (option code DEE). Check your data plate on the engine and it should show a rating of 235 BHP - the HO is 245 BHP.



Rusty

 

[kingdutch]

Data plate does in fact say 235... whoops!



Anyway, I wonder if there is anyone in my area who would let me try out their EZ before I made the purchase. I dont remember the hesitation being quite as bad when I bought the truck (2 yrs ago @ 76,000 - now has 115,000).

 

[nps]

How long have you had the 35" tires on? Perhaps they are the cause of the new sense of sluggishness.

 

[kingdutch]

That is a good point. . I have had 35s on for about 10 months. I do seem to remember thinking (after I picked up the truck from the tire shop) that it seemed a little slugish. I understand that the bigger tires have a greater diameter, but could there be something else happening in the drivetrain?



Thanks!

 

[nps]

You could have low fuel pressure. You could have a boost leak. You could have a bad MAP or IAT.



Check the boost hoses. The one connecting to the drivers side intercooler rubs on sheetmetal and will get cut. Bend the metal and replace the boot if this is the case.



The passenger side boot connecting the turbo to the downpipe rubs on the AC switch and gets a hole. Gently bend the pipe out of the way and replace the boot if damaged.



I'd recommend you put money into gauges before replacing the MAP/IAT.

 

[kingdutch]

Thanks for the information. I will be checking those hoses today. The FP gauge will arrive on Friday. I might have time to get it installed this weekend, maybe. I also purchased a Vulcan big line LP relo kit and a spare LP to keep under the seat (there is a guy on ebay selling new, tested LPs for $110).

Maybe I will have to use the new spare to replace the original - which was replaced once already at around 92,000 because I ran out of fuel.



Thanks!

 

[kingdutch]

Well... I inspected all of the rubber hoses going to and from the turbo/intercooler. All looked good, no tears. I will of coarse re-verify tomorrow.

I performed the real APPS reset (where you remove the APPS and rotate it to the correct voltage on pin #23 on C1). When I first check the voltage on #23 it read . 35. The back of my APPS says . 534, but I could not get the voltage on #23 to be anything greater than . 51 The truck now seems to be a little smoother (not much) on acceleration, but it now idles kind of rough. Should I set the APPS back to . 35?

My FP gauge gets here on Friday. It will be interesting to see what the FP is after the LP and filter.

 

[nps]

When I first check the voltage on #23 it read . 35. The back of my APPS says . 534, but I could not get the voltage on #23 to be anything greater than . 51 The truck now seems to be a little smoother (not much) on acceleration, but it now idles kind of rough. Should I set the APPS back to . 35?

I would leave it as close to the factory setting as possible. I don't believe the APPS affects idle (in neutral) so it is surprising to hear of a new 'rough' idle.



The IAT really doesn't have much affect on power - it moreso affects smoke and mpg performance. I removed mine and replaced it with a potentiometer to see what affect it would have - kinda like 'dial a temp'. Again - not much affect on power. I have since replaced it. Suggest you remove and clean yours.



The MAP moreso affects power because until the ECM sees boost it won't add fuel. Recommend you remove it and clean the orifice. You can also test it by feeding it compressed air and looking at the resistance. Believe there is a sticky post in the FAQs on what the good values should be.



Did you look real close at the driver's side lower boot near the fender? Can't believe with over 100K miles yours is still good. Take it off and look from the inside.

 

[kingdutch]

I will pull the MAPS and clean it with starter fluid and I will pull the turbo/intercooler boots and check them off the truck. Yesterday I just visually checked them while still attached.

The rough idle doesn't happen when I first start the engine. It happens after I drive it for a while (maybe 20 miles). This is a new development since I changed to VDC on the APPS.

As a result of checking and adjusting the APPS, I now have code P1693. The check engine light went out, but the code is still present. Am I correct to assume that this was triggered because the C1 plug was disconnected while I was doing the APPS adjustment?

 

[nps]

Was the truck running with the plug off?



P1693 means another code is in the ECU and evidently you aren't pulling it out with the key on/off trick. Go to Autozone and they will read it free with a scanner. Probably has to do with the APPS but you never know.



I'd recheck the APPS voltage - especially if you have it adjusted to the limits. Maybe something has slipped/changed.

 

[kingdutch]

Thank you. I will take it over to the local Autozone and have them read it. I never started the truck with the plug off, only put the key in the on position.

The process I used was; turn key to on; check voltage; put key to off; adjust APPS; key to on; check voltage; etc; etc. The check engine light came on as soon as I checked the #23 pin for the first time with the key in the on position.



The directions I was reading regarding the APPS adjustment did not clarify that I was not suppose to remove the screws entirely. As soon as I realized that, I put the whole thing back together... separating the two pieces didn't seem to harm anything.



The rough idle only was happening after a long run (30+ miles). When the truck first starts, it is fine.

 

[RAJohnson]

kingdutch the P1693 code is from when you reset the APPS and removed the C1 connector and turned ON or OFF the key. It will reset its self after about 20-40 start cycles.



When I did my APPS I got the same one



As far as when I reset my apps I left the key in the ON position, with my fluke attached to the correct wire and dialed her right in. Not a problem.