99 won't start

Ok,
I've had a problem with "no bus" as mentioned in these threads:
http://www.naxja.org/forum/showthread.php?t=973038
http://www.naxja.org/forum/showthread.php?t=976852

It started with just non working guages occasionally. I never had any problems with it not starting. The truck ran just fine. I took the guage cluster out, tweaked the pins, packed with di-grease and reinstalled. Still no guages, but it runs fine.

I realized after reading through mat6669's thread above, that I had replaced the ground strap with some 2 guage cable when I replaced my exhaust manifold. He mentioned having problems after doing battery cables as well. I replaced the cable with another strap and now my truck won't even start. Granted, its been sitting for about a month. I tried jumping it and my busted ass harbor freight multimeter shows that its got a good charge.

I decided that the cps is the ultimate answer. It was recommended occasionally for the no bus issue, but is also a key problem with no starts. I replaced that this afternoon and had autozone test/recharge my battery. It still will not start. The motor is turning over it seems, but it just won't fire.

Just to rule out the nss, I put it in neutral and tried starting it. Same symptoms. Pissed off and wanting results, I pushed the pedal to the floor and cranked it. It finally fired up but ran like ass. After letting it idle for about 25 seconds, i just turned it off.

I might have to put her down if someone can't help.

Any codes? If so, pull em......

If it does start but runs poorly, you have at least some spark, although the quality of that spark is still a question mark.

Testing would be the best way to proceed if you don't want to put her down....want to be sure what part of the starting equation is sick; the fuel part or the spark part. I'd start by testing the coil for a weak spark and also test your fuel pressure at the fuel rail and also your throttle position sensor. Should have about 49.2 psi at idle if my memory serves me correctly.

But why would it have changed? It ran just fine previously

If the motor cranks, it's not the NSS. TPS can affect starting too. You can check it with a voltmeter, but analog is recommended to check for smooth response without needle bouncing.

DeftwillP said:

But why would it have changed? It ran just fine previously

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Things gotta break sometime. The fact that it ran fine previously fits the pattern of most failures......Test your way to a solution. Good luck!

DeftwillP said:

Ok, ... had autozone test/recharge my battery. It still will not start. The motor is turning over it seems, but it just won't fire.
.
It finally fired up but ran like ass.
.

Click to expand...

On late Model Cherokees, disconnecting the battery or leaving the lights on and letting the battery run down, re-boots the ECM due to low voltage. When the ECM re-boots the idle settings are deleted. You will now have a difficult time starting, you may have to give it gas pedal to start, it will run rough and will stall if you don't keep your foot on the gas pedal. After a short period of time, the idle settings are re-learned and the engine will start and idle normally.

Ok,
It sounded like there was a vacuum leak somewhere so I checked the map sensor and the little rubber elbow. Everything was good there as well as with all of the vacuum lines that I could see. I took off the intake elbow and fired it up and noticed right away that the vacuum leak hiss is coming from the tb itself. Its sucking in so bad that if I stick my hand over the top, it will immediately suck it tight and choke out the engine. I don't recall that being normal.

Does the tps sensor have a port above and below the butterfly valve that could have stuck open?

DeftwillP said:

Does the tps sensor have a port above and below the butterfly valve that could have stuck open?

Click to expand...

I think you're talking about the idle air control with the two ports. It controls the amount of air going into the motor at idle. You can clean that out and see if that fixes your problem.

TPS has to send the closed throttle signal to the PCM to tell the IAC to be open to allow idle air flow. So we would have to figure out what the voltage needs to be to the IAC at idle. If that's bad, we need to trace back to the TPS. From recent research of my 2000 FSM, I know that the TPS voltage out should be 0.26 at idle. Seems like 99 would be the same, but I'm not sure.

Cleaning the IAC is also a simpler approach to a common problem.

I'll have to tear the whole tb apart tomorrow afternoon then.

Replace all ground cables with new and clean the connections then replace your TPS. Pushing your gas pedal to the floor and it starting indicates TPS. You must have good ground contact or you will have issues!!! I had the same problem as you described a while back and it turned out to be a bad ground cable/connection!!

I don't have to push the pedal to the floor anymore. It was just that one time to get it to start. Now I can start it, but it still stumbles like hell and sounds like a huge vacuum leak coming from my throttle body. I removed the IAC and cleaned the plunger which was very dirty and that didn't do anything.

I then decided to remove the throttle body to inspect closer. As I did, I noticed that one of the bolts holding it turned freely. Perhaps a certain chapter V/P stripped it when he was helping install my exhaust manifold (scott grrrrr). I know this formerly wasn't a problem though as I had put probably 1500 miles on it after the swap with no problem. I know it needs to be fixed but I don't think that its the problem.

Just to rule out that stripped bolt on the tb, can i use gasket maker between the tb and the manifold? Or better yet, between the tb and the spacer and spacer and the manifold?

Probably not. I think JB weld makes some kind of epoxy to build up threads. Check your auto store. Or tap out to next bigger size? Or helicoil?

Well seeing that I've got some kind of leak coming from what sounds like directly in the throttle body, I'm thinking its got to be the iac. If it suddenly goes bad, would it cause the idle to be erratic?

DeftwillP said:

Well seeing that I've got some kind of leak coming from what sounds like directly in the throttle body, I'm thinking its got to be the iac. If it suddenly goes bad, would it cause the idle to be erratic?

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sounds like you have a leak at the connection between the TB and manifold if one of the bolts holding the throttle body is loose. when i cleaned the tb on my 89 the gasket was torn so i made a new gasket. i just traced the pattern on a sheet of gasket material and cut it out.

but the iac could also be bad.

The IAC is ruled out as a new one didn't do it.

What size are the bolts that hold the tb down? I know it takes a 10mm socket, so 6mm? Would it be easy enough to try threading a 7mm into the hole?

I'm just going to take the tb off this weekend and completely tear it down/rebuild it.

DeftwillP said:

The IAC is ruled out as a new one didn't do it.

What size are the bolts that hold the tb down? I know it takes a 10mm socket, so 6mm? Would it be easy enough to try threading a 7mm into the hole?

I'm just going to take the tb off this weekend and completely tear it down/rebuild it.

Click to expand...

concidering the manifold is aluminum, you could thread in a larger bolt which will create there own thread in the manifold or just cut new threads with a tap.

yeah, I was thinking it's so soft that I could just start the next size up bolt without using a tap.

Ok, so I tore the tb completely apart and cleaned everything and replaced the gasket. I also rented a scanner and got a p1694 which would seem to suggest bus code/cps again. So I took the new cps back to autozone and got another new unit.

I don't know if my vacuum problem is still there around the tb, because now I'm back to not starting. It turns over very slowly but won't fire. It ran this morning, just not well.

Even though my battery was tested and I'm showing over 12 volts at the cigarette lighter, I'm starting to think I need to replace it now.

It's just unreal how many problems are happening all at once. This started with my guages not working and I've replaced the cps, iac, tb gasket, body to head ground.

What is the problem????