93v6 3vz-fe spits and bogs when cold...

[gen3-tony]

Sorry for the long post but I've been fighting this problem for about a year and I've replaced quite a few parts. I really would like to know if anyone here has a fix for this problem. I've modified the symptoms as it's getting worse lately.

Symptoms:
1. it starts great - hot or cold
2. it idles great cold
3. it idles a little rough when warm
4. it drives ok (but not great) when warm
3. cold startup, during the first 2 minutes of driving in open loop mode is terrible however: bogging down, some coughing or spitting, no power unless I go to W.O.T. Then it will at least go ahead and move. I believe the acis flap closes, timing is advanced, injectors are told to stay on longer, etc., under W.O.T., so I assume that’s how I am able to temporarily overcome this lean, cold running condition until the engine starts to warm up. After about 2 minutes, when the temp gauge gets off the C, then it works fine. I believe at this point the engine is in closed loop and begins using all the sensor inputs to give a better running engine than I’m getting with the cold mappings.
4. there are no C.E.L. or codes being stored on this obdc-I engine.

I've replaced:
-plugs (ngk platinum)
-wires
-distributor cap
-distributor rotor
-cold start injector switch (old one showed 75 ohms hot or cold)
-4"air intake, big black hose
-'fuel up' VSV (old one showed open)
-fuel filter
-PVC
-acis vacuum actuator


I've verified these parts are working:
-coolant temp sensor, ohms out good, hot and cold
-air intake sensor in the maf ohms out correctly closed/open/hot or cold
-o2 sensor (at least the one i can get to on the front - i pulled a vacuum with the wire disconnected to see if made it go lean .1v and it did, also revving it made it go rich .9v – doesn’t matter as it’s out of the ‘loop’ in open mode anyway)
-distributor timing is correct as i can see the mark on the flywheel with the 2 pins jumpered at the testing terminal block
-there's no fuel leaking into the vacuum portion of the fuel regulator
-pulling the vacuum tube off of the fuel regulator makes it idle up
-pinching the return hose makes the pressure increase (you can hear the fuel pump pumping harder)
-pulling a vacuum on the EGR makes the engine idle like crap (doesn’t matter as it’s out of the ‘loop’ in open mode anyway, but I believe this proves the egr is working)
-cleaned the intake
-checked the egr valve, but it wasn't gunked up
-cleaned the IAC and ACIS flap side too.
-clear air filter
-ran seafoam through it: half through the brake booster and smoked up the neighborhood and the other half in the tank of premium gas.
-checked out the distributor pickup coils for proper resistances. it's dry, no oil/water inside.
-checked out the ignition coil for proper resistances.
-had a 3-stage fuel injection cleaning performed by local shop.
-pulled the front 3 injectors to check them myelf and they were fine, but I can’t get to the back 3 as I stripped one of the 2 - 8mm hex head intake plenum bolts and can’t remove the intake now.

What I haven't done:
-put a fuel pressure gauge on the rail to verify actual fuel pressure numbers but the flow rate at the rail is about 1.5 qts / minute
-replaced or checked main computer/ecu/ecm
-had the timing belt replaced as it’s only got 50k on it. The last one I had replaced at 60k was like brand new so I’m dubious that the current belt could be so loose as to slip a cam tooth, but I’ll spend the $500 to get it replaced if that’s the only thing it can be.

What have I missed?
Any help is appreciated.
Tony

[Brian R.]

Welcome to the AF!

Here are some things (in no particular order) to think about and check if you can't discount them from experience:

Ignition coil (may be bad even with correct resistance at low potential of VOM)
Hot spark? (blue, not yellow)
Disconnected or leaking vacuum hose
Leak in intake manifold/cylinder head gasket(s) (torque?)
Plugged or partially plugged cold start injector (although idles cold)
Inadequate fuel pressure
IAC valve may still be partially plugged
Intermittent IGT signal from ECM
Bad Ignitor (try different one)
Air gap between distributor pick-up/inductor (0.008-0.020") or shaft wobble
plug gap (0.043", max 0.051")
TPS needs adjustment
Crankshaft Position Sensor signal (sensor or wire or connector)
Crankshaft Position Sensor inductor (scratched or dinged during timing belt replacement?)
Bad camshaft position sensor signal
Leak in injector O-ring (cracked or installed cocked)
Compression test

I think, since it runs best at WOT, then your best bet is assuming a leak into intake runner or manifold, since vacuum is lowest at WOT and leak into intake will have least effect. Also, open loop would be less able to compensate for leak than closed loop.

2nd best guess is MFI sensor problem. May still be ignition or ignition timing-related sensor.

I don't see how it can be the timing belt.

[davemac2]

Brian has some good suggestions, but I'm going to comment on some of the ideas:

1. I doubt it has anything to do with the cold start injector if the car starts ok. That only works at startup.

2. If it runs ok after warming up, I doubt it is the ignition system.

3. if the car is ok going up a steep hill after warming up, it is probably not fuel pressure related.

This happened to my wife's 93 XLE a year ago. It turned out to be cracks in the 3" rubber intake hose, so it was getting too much air and running lean. So I would suspect you have a similar issue of either too much air or too little fuel. So I would focus on the following:

1. fuel injectors. Make sure they are all firing on a cold start. Make sure the ECU is sending signal to them all.

2. Look for vacuum and intake leaks on all hoses as Brian suggests. Re-inspect everything. Pinch off the vacuum lines going to the VSV's right near their attach point at the engine manifold. Inspect the IAC hose that comes off the side of the 4" hose. Remove the IAC valve and clean it, replace the gasket that attaches it to the TB. Inspect the throttle plate and make sure it is fully closed when cold starting, and it moves freely. Check the throttle cable to make sure it moves freely and does not snag. Inspect the connectors and wires to the IAC and TPS.

3. If nothing pans out in 2. above, then start focusing on the intake manifold. Check if there are broken or loose studs attaching it to the heads. When it is running rough while warming up, try spraying carb or brake cleaner around the manifold gasket area and see if you get a change in the idle. Spray around the TB to intake manifold gasket area too to check for leaks.

4. As Brian suggests, you may want to do a compression test if you have not done one yet. There is a possibility that you have a bad head gasket that is leaking coolant into one of the cylinders after it sits for awhile.

good luck

dave mc

[Brian R.]

Originally Posted by davemac2

1. I doubt it has anything to do with the cold start injector if the car starts ok. That only works at startup.

2. If it runs ok after warming up, I doubt it is the ignition system.

1. I guess a leaking cold start injector would be more likely.

2. Ignition is low priority, but stranger things show up as ignition problems. I wouldn't discount them. Particularly a wobbly distributor shaft (inducter gap) that tightens up when warm, or a coil that has a cold crack in the insulation that seals when warm. Dave is probably right, but keep your options open. You may have more than one fault.

[davemac2]

well, this is true. you never know. If it is a leaking cold start injector, you would think it would just run rich rather than rough. Maybe he can try to pinch off the cold start injector fuel supply hose and see next time?

cheers

dave mc

[gen3-tony]

okay, thanks for all the replies so far.
here's some stuff I didn't put in my first post.
1. i've sprayed TB all over the place hot and cold with no difference in idle speed.
2. i've checked all hoses i can see and they don't have cracks.

i checked resistances on the distributor when it was cold and they were within tolerances. i guess the gap could be bad in the distributor. i can check that or replace the pickup coil(s). my vom is rated @ 1megohm/volt so i believe it to be accurate. i couldn't make the distributor shaft wobble with my hands. how much pressure would i need to apply to make it wobble?

i can't check the back 3 injectors cause i screwed up the 8mm hex head allen bolt that goes into the intake plenum, so I can't remove the intake and can't access the injectors. can i assume they are firing cold if they're firing fine hot or is that faulty logic? note that i did replace the 4 o-rings per injector on the front 3 injectors that i could get to though.

the cold start injector isn't leaking. it sprays fine - i removed it to be sure. I'm pretty sure that'd make it run rich but the plugs show white, so i'm pretty sure it's a lean condition i'm fighting.

i haven't done a compression test, but it doesn't use excessive amounts of oil it should be close enough tolerance for an old engine. also, no loss of coolant or bubbling on the dipstick or white smoke or sweet smell on startup.

tps is adjusted to .021mm for the break point per the manual.

1. any votes for a slipped timing belt?

2. how about any way to check the igniter without buying another one to put in my spare parts bucket.

any other ideas please? I'm open to everything at this point.

thanks much.
tony

[Brian R.]

For a wobbly distributor shaft, the air gap on the inductor will show that. There isn't alot of tolerance for that gap.

Fuel pressure

Manifold leak

I don't think timing belt is possble.

You can try e-mailing Toysrme. He is an expert on this engine.

[davemac2]

If you have not pulled the IAC valve off totally for a cleaning, then I think that should be your next step. There appears to be two valve seating surfaces on the IAC: the one that seats inside the TB, and the internal one which controls air going directly into the intake manifold past the TB. (I'm looking at the factory manual diagram.) It's a long shot since I think this IAC is less susceptible to clogging unlike the smaller 4 cyl version.

You may want to try a bolt-out to get that allen or star head out of the intake manifold to access the rear injectors and inspect the manifold for cracks as well as its gasket, or is it too difficult to get to it? I think you are going to have to do this eventually to find this problem. You can try to rock the engine forward maybe by removing the dogbone mount at the front and using a cable puller or something to rotate it forward a bit.

Something else you can maybe try is to pull the plugs just before a cold start when you know it will run bad and inspect them. Pull the backs too.

Brian, just curious, why do you think it would not be a slipped timing belt? I'm just guessing since I don't have enough experience to say, but would the ECM be able to compensate for a slipped belt in closed loop somewhat by playing with the Distributor timing advance? I wonder if there is a way to check that without having to everything off the front of the engine? It looks like it's about 1-2 hrs worth of work to remove the timing belt cover to have a look. May be worth just going ahead and changing it if you feel confident enough to do it and it due.

dave mc

[Brian R.]

It seems that it would be extremely unlikely that the timing belt would skip one or more teeth on both cam pulleys. I think this is what would be necessary in order for the ECM to compensate the ignition timing for the slipped belt. If one cam is retarded and the other is correctly timed, then I would expect that the engine would never run well, hot or cold. At least, that has been what I've seen, but I guess there are no guarantees. Actually, I've never heard of a belt only slipping one tooth on one cam pulley. This small change may cause what he is seeing, but I have no experience with this exact problem.

I think the timing belt (valve timing) will be checked (if a significant number of teeth have been jumped) by a compression test to prevent unnecessary work in exposing the front of the engine. Bad valves or valve adjustment would also show up either cold or hot compression testing. A whole bank of cylinders being bad would indicate timing belt.

[gen3-tony]

okay thanks guys for all the help. I'll work on getting that 8mm hex head bolt out so i can get the plenum off so i can remove the injectors to see if they are plugged somehow. i'll report back when i am able to do this as I just had triple bypass surgery and am not able to pull a lot of torque yet. and i suspect it will take a lot to get that bolt out. thanks again.
tony

[Brian R.]

Use a long extension on a breaker bar handle (and high-quality penetrating oil) to prevent your needing to apply alot of force and potentially injure yourself.

[davemac2]

Originally Posted by gen3-tony

i'll report back when i am able to do this as I just had triple bypass surgery and am not able to pull a lot of torque yet. and i suspect it will take a lot to get that bolt out. thanks again.
tony

My god man, take it easy until you have fully recovered and don't worry about the car. We'll be here when you are ready.

Best of luck with your recovery.

Dave Mc

[gen3-tony]

thanks much guys for your help. i'll report back in when i find out something new. much appreciated.
tony

[gen3-tony]

Well, i felt better today so i used a bolt out and got that intake plenum off. I checked the rear injectors and they seem to spray fine. also, i verified the rear plugs were still clean and seated. lastly, there were no hoses with cracks or loose fitting. it's all back together and still bogs and spits for the first 60 seconds or so when it's cold, under load. i'm not sure where to check next?
1. coil
2. igniter
3. distributor (not the cap or rotor as these are new)
4. timing belt (slipped tooth/teeth).
5. ecu
any and all suggestions welcome. thanks.
tony

[gen3-tony]

well, today i took out the distributor and the shaft doesn't wobble and all 3 coil pickup clearances are within specs (.012), with no sign of arcing, etc. when i replaced the distributor and started to check the timing, i noticed something i thought odd. the timing light seems like it misses every so many cycles or cuts out. its not the timing light because it only seems to do it on some of the wires. (the wires are new). i aim the light at a dark surface and turn it on and when the clamp is on the #1 , #3, and #5 plug wires, the light flashes aren't even. they're what i'd call sporadic, with intermittent misses, especially when i rev up the engine. does sound like anything or is it normal behavior?
thanks
tony