OK. A week ago I noticed that my 98 2dr 4wd began doing a little chugging or dropping power just for a second while at highway speed. It felt like the gas had water or maybe a pump going bad. I put some ISOheat in it but it didn't seem to help. BTW, this began just after I replaced all plugs/wires/cap/rotor. It ran fine a couple of days after that, but then it started raining and rained for a week, which is when the problem began. I took it to a dealer last Thursday and they kept it all day, then said that there were misfire codes and that they would replace the upper and lower intake gaskets. When they told me $762, I said I'd do it myself. I just can't afford that right now, but thought it would only get worse. This Sunday I tore the engine down and installed the gasket set. I just got everything back together tonight, but it's in even worse shape. I did everything by the book. Drained the coolant first. Tore the motor down labeling everything. Marked the dist/rotor before removing. I cleaned everything off good and, other than lots of carbon on the intake, everything looked good. I put it back together, refilled the coolant, and changed the oil. When I started it up, it immediately began idling rough. I suspected a vaccum leak, but can't find one unless some gasket in the upper intake didn't seal right. I noticed that it doesn't seem to have a problem once reved up, but when you first touch the gas it almost dies, then revs up. No leaks I can see. My SES light came on, but I'm afraid to drive it to the autozone, so I'll go buy a code scanner tomorrow.
One big weird symptom...my tach now never moves. It stays at 0 no matter what. I found one thread where someone mentioned the Crankshaft Sensor. I never touched that, but it is possible some coolant ran down over it. It's located on the bottom of the engine, so that shouldn't be a problem...should it? Any ideas?

 

Did you make sure to plug the CMP sensor back in (plug from the distributor)? The CMP sensor (CaMshaft Position) is what is used for the tach signal. That could cause it to run rough as well as a CEL...

 

Um....Nope. That was it. I forgot that the connector fell back down behind the engine. Thank you very much.

 

How is the truck running now? Did that fix everything or just the tach??

 

Exodus, if your autozone has the tool lending service, they will let you borrow one of their code scanners if they have one available.I had topay like a $150 deposit, but whenI took it back in a couple of days later, theygave me all of the deposit back. Just an fyiin case you need one in the future.

 

swartlkk
Yep, that seems to have fixed the bad idle/dying at first throttle problem as well as the tach. It's running fine (didn't get to do a road test because it got dark and I don't think I have the coolant level right.
It still may do something funky. I'll find out this afternoon.

DukMan
You know, I called them about that. They told me they would scan it for me if I brought it by, but that they didn't loan those out.

 

Alright. I found an autozone and rented the scanner. The code was for the Camshaft Position Sensor circuit, which is what I plugged back in per swartlkk. I cleared the code and let the truck run a few minutes, but I wasn't getting heat. I put coolant in the radiator but not to the top (I guess this is wrong per my searches here). Do you fill the radiator with the front end lifted or can you do it level? Engine running right? Also, has anyone here found the hose from the radiator (cap area) to the coolant overflow tank to be blocked. I have noticed that I have NEVER seen the level in that tank change. I got curious, since I figured it should have pulled coolant if I didn't put in enough, and started squeezing the hose to see if it had a plug. One section barely compresses, while the rest compresses fine. I think I need to take it off and clean it out. Also, replacing the idler pulley didn't get rid of my belt-area chirping like the GM techs said it would. I've replaced the tensioner and idler pulleys. I also replaced the water pump while doing the head gaskets. Could the coolant level be so low that the pump is making this noise now?

 

I would replace the overflow hose as well as the radiator cap if you haven't done so already. Stant is pretty much the best you can buy for radiator caps.

Anyway, You can fill the radiator with everything level, but the air may not work its way out as easily as it would if the front end was high, with the front passenger side being just a tad higher than the driver's.

As far as the belt chirping, have you narrowed it down to one pulley/location?

 

OK an update. I found that the hose from the bottom of the coolant overflow tank was completely stopped up. I replaced that and cleaned the tank out pretty good. I put it back and and filled the radiator to the top, then jacked up the front passenger side and started the engine and made sure to keep adding until it stayed full. I also had the proper level in the overflow tank. After all this, I let the truck warm up (chirping stopped, btw...seemed to be coming from the alternator) and drove it down the street. It was ok at first, then when I got on a flat level road I noticed it chugging again at steady throttle. Damnit. I drove it back to the house and, just in case, hooked up the code reader I rented from Autozone. Now it's giving me a P0147. Would I have somehow disconnected the 02 sensor circuit, or is this because it chugged?

 

Another update. I checked the fuel pressure and it's about 60 and doesn't leak down. When I start the truck and let it idle the pressure is steady at ~52. What could cause the truck to idle ok, but start choking when you first start off and then occassionally at highway speeds? I've searched and searched here. I see EGR and Spider assembly's mentioned. I'm pretty sure I didn't have leaking injectors before I did the intake gasket swap...