Slow Start, Hesitation, Backfire. - At A Loss.

[Megadan]

This truck was having the problem before it went down for the transmission replacement, and then the cylinder head.

Let me start with what's new and whats done:

All new ground cables - 1 Ga. welding cable for the main battery ground. All other engine grounds are new or cleaned up (dipstick side, and cylinder head).  
ECU ground/harness "mod" done via Cruisers writeups.  New TPS connector and pins with completely new ground wire run.  TPS is also adjusted to the 17% range indicated in writeups.
All new gaskets and hardware for manifolds.  All tightened and re-checked to factory torque specs.  

New O2 sensor with properly made extension harness using weatherpack connectors and new 16ga wire - and tested to verify signal integrity I might add.
C101 connector was pulled apart and cleaned.

New Map sensor and connector - old map hose nipple was cracked at the base and leaking, connector was broken.
All new vacuum hoses.
New fuel pump (old one was very loud and OE) New injectors (corroded, fouled and not spraying evenly). New fuel filter (duh lol) and the FPR was repalced not too long ago by previous owner.  Pressure is stable and exactly where it should be.
New CPS was installed when I did the transmission, and I did the "mod" to open up the right side mounting hole a little to push it closer to the ring gear.
All new plugs, wires, cap rotor. The plugs are traditional copper cores gaped to .035
Exhaust manifold replaced with Pacesetter... yes, I know...  It actually fit just fine surprisingly.

Now, Just so it is known it was having this problem before hand.  It used to have a very unstead idle and would fluctuate around 450-550, but now it is actually holding fairly steady at 600.  You can hear it fluctuating a tiny bit at idle still, but much more slowly and only by ear as it doesn't show on my Tachometer at all.  It will no longer stumble and fall on it's face with a quick rev, or outright die like it used to.  With everything replaced out of necessity (besides the header...) or common sense, and everything else that people often say to check to others that have this problem, It still does not want to start without giving it some foot action on the throttle (will try to start when I let off after opening it), and when it does, it occasionally stumbles a bit and a backfire.

The only thing left that I haven;t touched yet is the actual ICM, Coil, or the Cam Sensor/Stator pickup in the distributor.  It is acting like the timing is off though instead of it being a fueling problem.  Exhaust neither smells rich not lean - open pipe at the moment.  Aside from those two issues, it runs like a champ!   My only other guess is that the TPS has a flat or dead spot in it's signal, because I have noticed that the stumble seems to happen around the same RPM range.

Looking for advice, tips, tricks, etc.  Insights are definitely welcome.  
 

[Jeep Driver]

This truck was having the problem before it went down for the transmission replacement, and then the cylinder head.

 

Let me start with what's new and whats done:

 

All new ground cables - 1 Ga. welding cable for the main battery ground. All other engine grounds are new or cleaned up (dipstick side, and cylinder head).  

ECU ground/harness "mod" done via Cruisers writeups.  New TPS connector and pins with completely new ground wire run.  TPS is also adjusted to the 17% range indicated in writeups.

All new gaskets and hardware for manifolds.  All tightened and re-checked to factory torque specs.  

New O2 sensor with properly made extension harness using weatherpack connectors and new 16ga wire - and tested to verify signal integrity I might add.

C101 connector was pulled apart and cleaned.

New Map sensor and connector - old map hose nipple was cracked at the base and leaking, connector was broken.

All new vacuum hoses.

New fuel pump (old one was very loud and OE) New injectors (corroded, fouled and not spraying evenly). New fuel filter (duh lol) and the FPR was repalced not too long ago by previous owner.  Pressure is stable and exactly where it should be.

New CPS was installed when I did the transmission, and I did the "mod" to open up the right side mounting hole a little to push it closer to the ring gear.

All new plugs, wires, cap rotor. The plugs are traditional copper cores gaped to .035

Exhaust manifold replaced with Pacesetter... yes, I know...  It actually fit just fine surprisingly.

 

Now, Just so it is known it was having this problem before hand.  It used to have a very unstead idle and would fluctuate around 450-550, but now it is actually holding fairly steady at 600.  You can hear it fluctuating a tiny bit at idle still, but much more slowly and only by ear as it doesn't show on my Tachometer at all.  It will no longer stumble and fall on it's face with a quick rev, or outright die like it used to.  With everything replaced out of necessity (besides the header...) or common sense, and everything else that people often say to check to others that have this problem, It still does not want to start without giving it some foot action on the throttle (will try to start when I let off after opening it), and when it does, it occasionally stumbles a bit and a backfire.

 

The only thing left that I haven;t touched yet is the actual ICM, Coil, or the Cam Sensor/Stator pickup in the distributor.  It is acting like the timing is off though instead of it being a fueling problem.  Exhaust neither smells rich not lean - open pipe at the moment.  Aside from those two issues, it runs like a champ!   My only other guess is that the TPS has a flat or dead spot in it's signal, because I have noticed that the stumble seems to happen around the same RPM range.

 

Looking for advice, tips, tricks, etc.  Insights are definitely welcome.  

 

Unplug it and see if the stumble goes away.

[Megadan]

When the TPS signal was all out of whack it had the same problem, but worse.  I will unplug it tomorrow and see what happens, although I am not a big fan of testing sensors that way.  I have thought about doing a sweep test with the throttle and a multimeter, but an analog display would be much better at picking that up than my cheap little digital I am currently using.

In the meantime, let's assume that the TPS is good.  Any good way to test the Stator/pickup in the distributor, or should I whip out the good ol' timing light?

[Megadan]

Revisiting this.  I added an extra ground from the battery to the chassis, a new ignition coil,  and replaced the extremely loud fuel pump with a new carter in-tank (it's so quiet now!).  I also tested a new TPS, but returned it when I noted that it did not make any difference (rules that out)

The coil really helped to smooth out the engine and did get the idle under control.  It still fluctuates a tiny bit, but nowhere near as bad as it used to.  So that was part of the problem, but not the only one.

With the ignition having strong spark again, the stumble I have is much more prominent now when it happens, as are the occasional loud bangs out of the exhaust.  I even got a spit of flame on one.  It only does this if I get on the throttle sharply.  If I press on the pedal nice and smooth, not one problem.

Since it seems to be a timing issue, that leaves me with only a few ideas of where the problem is that I have listed below.  Any ideas, opinions, or suggestions?

1. ICM is somehow bad

2. Sensor in the distributor is bad/weak

3. ECU is to blame.

 

[cruiser54]

The sensor in the dizzy is not an issue. If you wanna check, unplug it.

 

Have you indexed your distributor? 

 

If it's off, the spark, which is triggered by the ECU, may be having to jump a long ways to get from the rotor tip to the terminals inside the cap.

[Megadan]

The sensor in the dizzy is not an issue. If you wanna check, unplug it.

 

Have you indexed your distributor? 

 

If it's off, the spark, which is triggered by the ECU, may be having to jump a long ways to get from the rotor tip to the terminals inside the cap.

 

No, I haven't indexed it yet, but that was actually my next step today following your write ups.  I know it's a timing issue, but not what it is caused by.

[cruiser54]

 

The sensor in the dizzy is not an issue. If you wanna check, unplug it.

 

Have you indexed your distributor? 

 

If it's off, the spark, which is triggered by the ECU, may be having to jump a long ways to get from the rotor tip to the terminals inside the cap.

No, I haven't indexed it yet, but that was actually my next step today following your write ups.  I know it's a timing issue, but not what it is caused by.

Index the dizzy next.

[Megadan]

Well, I am trying to index it.  My problem is.  There is no timing mark where everybody shows it to be.  I have turned it over repeatedly, using my eyes, and even my fingers, on that back edge.  It's perfectly smooth all the way around.  Also, the marked part of the cover over the crank sticks out so far that it covers the first two grooves on the pulley and you can't even see the back part of the crank pulley.   I am at a complete loss as to how to get this thing at TDC.  

Then to make things better, it looks like somebody tried to index the distributor, but they ended up cutting the hold down tab and not the locating tab on the distributor.

I did notice one thing though.  I looked down inside the distributor and noticed that it's filled with oil.  So it must have a bad shaft seal.  

[cruiser54]

Get another dizzy then. Index that one. Be sure it seats fully as some remans have a longer shaft not allowing the dizzy to seat perfectly. 

[Megadan]

I did.  I ordered a new Distributor, and found a salvage company on e-bay selling the hold down tab for $4 so I ordered one of those too.  I figured out what this person did.  They tried to index the distributor, but they cut the hold down, and not the distributor.  Thanks for the advice and help.

I did manage to finally find the timing mark.  I had to use my finger nail and slowly turn the crank until it caught.  So it's at least at cyl 1. TDC now.

[Megadan]

So, new distributor was installed for about 20 minutes.  It DID solve the stumble and backfire problem.   I also noticed that with the engine at TDC, the new distributor already put the rotor in the correct position one would get from indexing.  I should have known better than to run it until I got the new hold down in, but I tried to use the old one temporarily...and well the ear on the distributor and part of the base at the seal all broke off as once piece.  Luckily, they are sending me a new one as a warranty replacement.  I should have a proper hold down by then as well.

I still need to figure out what is causing the idle to fluctuate.  I have ruled out pretty much everything.  The only thing left that I can think it would be is the IAC circuit itself (or something causing the IAC to activate and deactivate).   The valve is new and the whole TB was cleaned.  On cold starts, it only fast idles at 1000-900 rpm for about 10 seconds and drops down to 700, and eventually ends at 600rpm, and all in 1 minute.  The engine is still ice cold when it settles into it's idle.  I am not familiar enough with this platform to say that is abnormal, but every vehicle I have ever owned stayed at a fast idle longer than that on a cold (below freezing) start.

[Megadan]

Ok, I finally got around to installing my new-new distributor.  I still notice a small miss from time to time at idle, but I also haven't quite dialed the idle in yet.  It nearly holds steady now and only fluctuates maybe 30rpm once it is up to temp. a little more when cold and the IAC is actually doing more.  

Anyway, I figured out what the actual problem was.  The shaft had so much side to side play that the rotor was contacting the terminals in the cap.  I figured this out when I pulled the cap from the old one and found that the entire contact end of the rotor was broken off and laying at the bottom of the dizzy in quite a few pieces.  That and I could get it to move side to side by hand.  That explains the oil in the distributor and the many other problems I have had.  

It runs so damn smooth now... I love it.