1995 Astro has very rough idle hot OR cold

A few details...

This is actually a 1995 GMC Safari, so all Astro info should intrechange. W engine, ~180K miles. This is just a van that we use to get parts 'n such, everybody loves driving the crap out of it. It has ALWAYS run excellent, with around 19MPG.

It has always idled rough intermittently, but only when hot. As soon as there's any pedal, it's smooth as silk. Yesterday, the engine began idling VERY badly (instantly...no gradual degradation), to the point that it will barely stay running. But if you get it moving, it's fairly smooth.

Diagnosis so far...

- New Autolite double platinums, cap, and rotor about 15K miles ago.
- Fuel filter replaced every year.
- Fuel pressure 62psi, key ON engine OFF. Pressure after 5-10 minutes of key being off is still 60psi.
- New cap, rotor, and wires yesterday. No change in idle quality. Spark easily jumps a gap of over 1".
- No SES lights/codes.
- Pulled #4 plug, appears fuel fouled.

Sensors:

- TPS resistance sweep seems fine, very linear. Can't recall exact numbers. No bad spots/shorts detected (i.e. idle/part throttle position).
- IAT replaced for good measure.
- CTS resistance sweep of both sensors (L. Side head and front of intake) also seems fine, very linear. Temp simulated with heat gun. Can't recall exact resistance numbers.
- MAP sensor unchecked so far.
- EGR removed, valve appears free, and seated. Port(s) under EGR in intake not clogged. (By the way, should it retract when key moved to ON position?)
- Removed IAC, wasn't dirty at all. Pintle extends when key moved to ON position.


So...does the presence of good fuel pressure (that doesn't leak back down) rule out the injector/spider assembly? I'm at a bit of a loss here.

Thanks...

Your fuel pressure and leakdown are within factory specs. 60 to 66psi key on engine off pump running. Must remain above 55psi for 3 to 5 minutes after pump shuts off.

EGR valve must close, (extend) while cranking and at idle. Check EGR signal return voltage while idling, and post results.

Plug #4 fuel fouled MIGHT be a clue, but check EGR first.
(Never had good luck with any plug other than AC Delco in 4.3L engine)

...Check EGR signal return voltage while idling, and post results...
What's the proper procedure for this?
Plug #4 fuel fouled MIGHT be a clue, but check EGR first.
(Never had good luck with any plug other than AC Delco in 4.3L engine)
What is the PROPER Delco plug to use? The Autolites don't seem to hold up worth a damn on these.

Thanks,

If the engine has a linear EGR valve, (5 wires in the connector, and no vacuum line), the brown wire should be less than .5 volts, with the engine idling. If the EGR valve does not have an electrical connector, there should be zero vacuum on the vacuum line while at idle.

Plugs can be AC Delco CR43TSM or 41-803 AC Delco Platinums. Either one will work well.

Thanks old_master,

Quick question...what kind of life expectancy do you see out of the standard resistor plugs (CR43TSM), assuming the fuel and ignition systems are up to snuff?

Sounds like my 94--after changing plugs dist cap ect... and working well into the night, I noticed a spark coming from inside the doghouse... I changed the plug wires and she is smooth as silk..

Thanks old_master,

Quick question...what kind of life expectancy do you see out of the standard resistor plugs (CR43TSM), assuming the fuel and ignition systems are up to snuff?

Platinums usually are good for 100,000 miles. The CR43TSM plugs, I would check at around 50,000.

Platinums usually are good for 100,000 miles. The CR43TSM plugs, I would check at around 50,000.

Have you tried to find to find a CR43TSM lately? I searched around locally and the consensus is theyve been discontinued. Checked some data that indicated theyve been "superceded" by the CR43TS. Some are listed on online parts places for over $5 a pop....passed on that idea, went with the CR43TS. Question is... why were they discontinued and whats the real difference between the two plugs?

Have you tried to find to find a CR43TSM lately? I searched around locally and the consensus is theyve been discontinued. Checked some data that indicated theyve been "superceded" by the CR43TS. Some are listed on online parts places for over $5 a pop....passed on that idea, went with the CR43TS. Question is... why were they discontinued and whats the real difference between the two plugs?

Advance Auto Parts has them:

http://www.partsamerica.com/productdetail.aspx?MfrCode=ACD&MfrPartNumber=CR43TSM

BTW, the van is running 100% better after a plug wire change. I actually haven't changed the plugs, but the idle quality, driveability, and mileage came right back up to par.

Update / New problem...

The van now starts just fine. Running fuel pressure is ~56psi. (???) It will idle for several minutes, but when it's put into gear, the engine sputters and nearly dies. After a minute or so of light throttle (almost idling) in gear, it won't stay running, and won't restart. Let it sit for a day, and it will finally restart, but dies again once it's attempted to be driven.

Fuel pressure drops quite a bit when this is happening. The funny thing is, there's still over 40psi of fuel pressure when trying to restart the van, but it just will NOT re-fire. Spark has been checked...there's definitely fire. When cycling the key, I can hear the pump run for 1-2 seconds.

Any ideas?

One additional question...

The local parts house is Advance Auto, and I'd prefer to stick with them [for a number of reasons]. They don't stock the CR43TSM. They'll order them, but the total cost would be ridiculous. They do, however, stock the CR43TS. Is this an acceptable plug for the 4.3?

Update / New problem...

The van now starts just fine. Running fuel pressure is ~56psi. (???) It will idle for several minutes, but when it's put into gear, the engine sputters and nearly dies. After a minute or so of light throttle (almost idling) in gear, it won't stay running, and won't restart. Let it sit for a day, and it will finally restart, but dies again once it's attempted to be driven.

Fuel pressure drops quite a bit when this is happening. The funny thing is, there's still over 40psi of fuel pressure when trying to restart the van, but it just will NOT re-fire. Spark has been checked...there's definitely fire. When cycling the key, I can hear the pump run for 1-2 seconds.

Any ideas?

I have owned 4 astros and have probably been bit by all the bugs--There is a short black hose that attaches the fuel pump to the fuel pump assembly--This hose on my 94 deteriorated --and would leak fuel when under strain causing the same symptoms you are describing... The stock hose was of low quality and just fell apart--One would assume a fuel pump problem but after scratching a hole in my head and causing me to age beyond my years, I dropped the fuel tank and found the situation I described ---It is only abou 2 inches long and attaches the fuel pump to the assembly--I cleaned the fuel pump out because it had sucked some of the erroded material within and bought a replacement and two small clamps--I would reccomed replacing the pump if this is the original pump---Hope this helps--it happened to me--also I would not be too quick to rule out the spyder assembly as this has been the problem in many of the 95's. I believe this was the first year that a high preassure fuel injected system was put on ALL of the 4.3 engines in the Astro Vans...

GM does not publish an "engine running" fuel pressure, far too many variables involved. Key on, engine off, fuel pump running, pressure must be 60psi to 66 psi. After the pump shuts off, pressure must remain above 55psi for 3 to 5 minutes.