astro misfire

I currently own a 1999 astro and purchased it used in 2002, ever since the time of pick up the van misfired in cruise on hiways and sometimes from a stand still when accelerating under normal circumstances, i did replace all the usuals , wires, coil, plugs, cap and rotor, and no joy the on board computer is not much of help because it does not give me any codes. I even trial swaped the mas airflow, tps and the ignition module and that did not improve my luck because it still misses. What i did notice though is that engine is cold then its beautiful till it reaches operating temp, and when it starts to misfire and i go to WOT operation the miss dissapears and it accelerates normally and smoothly. Any suggestions would greatly be appreciated - thanx.

Welcome to AF on your first post.
You may need a good engine capable scanner to get in there and find what cylinder is missfiring. And go from there..
There is a injector test that a good scanner can run to rule out dirty injectors.
How is the fuel pressure and what kind of plugs did you feed it.
What is the cam retard reading on the dist?
Is it a 4.3 w engine.
Can you tell what cylinder is missfiring?
MT

i have purchaced on line the obd2 vechicle explorer, which runs on my laptop, but am unable to retreive the misfire cylinder since the onboard comp. is not latching any codes, the only code that i did get lately is the emmisions code po420 which points to the last oxygen sensor down stream. That is all for codes, and like always it starts like a dream and idles, just on slow acceleration or highway cruise it bucks. The engine is stock 4.3 - i thought that it had throlte body injection sys ?? correct me if i am wrong please - its hard to see in there (small place). Oh ya - the plugs are bosh platinum single electrode with 1 gnd post - , i had the multi platinum bosh with 4 gnd prongs before and found no gains from them. Also had ngk low res wires before and same - no gain so i went back to a new set of stock wires.

i have purchaced on line the obd2 vechicle explorer, which runs on my laptop, but am unable to retreive the misfire cylinder since the onboard comp. is not latching any codes, the only code that i did get lately is the emmisions code po420 which points to the last oxygen sensor down stream. That is all for codes, and like always it starts like a dream and idles, just on slow acceleration or highway cruise it bucks. The engine is stock 4.3 - i thought that it had throlte body injection sys ?? correct me if i am wrong please - its hard to see in there (small place). Oh ya - the plugs are bosh platinum single electrode with 1 gnd post - , i had the multi platinum bosh with 4 gnd prongs before and found no gains from them. Also had ngk low res wires before and same - no gain so i went back to a new set of stock wires.

Code 420 could be caused by a lot of things besides the 02 ssensor.
You need to work on the missfire first as it could be the cause of code 420.
Also the bosh plugs are not the best plugs for it.
I would try a set of ac-delco plugs the book calls for and go from there.
Is the check engine light flashing or just on steady.
A flashing engine light is a missfire.
If the ac delco plugs do not cure it you may have to find someone with a engine capable scanner to find the miss firing cylinder or other problems.
Also check fuel pressure and fuel filter.
Good luck
MT

No- no flashing codes, that would be too simple, ya i did gather that the po code did not aid me with the miss problem, i eliminated the fuel suppy from my list since every time the problem would occur and i went to WOT operation the hesitation (miss) went away, typical low pressure due to bad filter would start starving the engine in WOT but this thing will do past 140 no prob. Reading around, some people suggested a egr valve to be the problem but if this is a stepper unit (not vacum) then the on-board comp should flag it. Also reading around, I am surprised at the number of people with a similiar problem, but a solution is difficult to obtain. All the dealer wants to do is cap/rotor, wires and coil pack change, oh ya and that will bring me up to $900 with labor.

cam retard reading - is that acquired from the obd2 or do you have to attach a special tester to the distributor ??

cam retard reading - is that acquired from the obd2 or do you have to attach a special tester to the distributor ??

A blinking check engine is what clues you or tells you that the engine is actually missfiring.
The cam retard reading is found with a engine capable scanner.
Just OBD11 may not show you all of the stuff or do all all of the test.
First thing.
Drop them bosh plugs in the trash can.
You need to start with a good set of ac delco plugs.
Flel pressure needs to be checked with a gauge and make sure it is up to par.
You can not tell by feel or just engine running on fuel pressure.

Here is some tips on going to the dealer or good repair shop.
Tip on going to the dealer
Ask that only a factory certified gasoline engine performance specialist work on your car.
Not all dealerships are concerned with how repairs are dispatched, and not all dealership techs bother to take advantage of the training offered by Ford (the vast majority of which is paid training). If the dealer is uncooperative, ask for your money back and call around for a dealer that will accommodate you.
And some tips on finding a good repair shop.
heck around Ask around
Word of mouth.
Family friends coworkers neighbors business people and delivery people.
Mailmen and parcel delivery people get around and notice a lot of stuff.
Even a good parts house knows what shops are good and not good.
Chamber of commerce and better business bureau and city hall.
If you find a good referral to a repair shop go look them over and talk to them.
Look for a clean looking busy place with nice people running it.
Ask a few questions and ask about their qualifications and training.
Not all places have trained tech/mechanics.
If they do not find a place that does.
Even all dealers do not have all trained techs/mechanics.
And last but not least some tips on that fuel pressure.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

I'll second the vote to throw the Bosch plugs back across the Atlantic, or as far eastward as you can. Install a set of Delco full platinum plugs, not the single platinum side electrode POS plugs. Use AC 41-932 (P/N 25321614), and nothing else. Check and set the gaps carefully, since they do not necessarily come out of the box with the correct gap.

Make sure the PCV valve is the correct part for your application and is clean.

Use 8mm silicone resistance ignition wires only.

Since you have scanning, get teh engien up to normal operating temperature, and check the injector pulse widths for each cylinder at idle and at 1,800 RPM.

As MT suggested, a fuel pressure reading both running, standing (prime) and after shutdown might be helpful.

where is the best place for a fuel pressure tap-in on the van ? and thanx for the plug # - will have to visit a dealer and pick up a set. I have spent a lot of time on chev v8's and never found an engine so finicky.

where is the best place for a fuel pressure tap-in on the van ? and thanx for the plug # - will have to visit a dealer and pick up a set. I have spent a lot of time on chev v8's and never found an engine so finicky.

Top left rear where the fuel lines come over the engine there should be a schrader valve on the pressure line to tap for fuel pressure.
A gm fuel pressure gauge should have the right fitting to tap on there.
MT

thanx lots for all your help, i was just reading around on the principals of injection control with the use of long fuel trim and short fuel trim. Interesting stuff, but i can see how it can be confusing to mechanics with no closed loop circuit knowledge. My profession is electronics and that is part of fundamental knowledge for the field. Now i see the need for the long spiel on locating a knowledgeable mechanic.

thanx lots for all your help, i was just reading around on the principals of injection control with the use of long fuel trim and short fuel trim. Interesting stuff, but i can see how it can be confusing to mechanics with no closed loop circuit knowledge. My profession is electronics and that is part of fundamental knowledge for the field. Now i see the need for the long spiel on locating a knowledgeable mechanic.

You are welcome.
And yes sometimes you have to hunt for the good ones.
Good Luck
MT

Andre L.
I fought this problem for 2 years. I changed all of the same things that you changed. The only thing that solved my problem was a brand new, direct from the dealer, distributor cap. I know it sound crazy but after I put the AC Delco cap on that I purchased from the dealer service center the problem went away.

Andre L.
I fought this problem for 2 years. I changed all of the same things that you changed. The only thing that solved my problem was a brand new, direct from the dealer, distributor cap. I know it sound crazy but after I put the AC Delco cap on that I purchased from the dealer service center the problem went away.

Welcome to your first post on AF.
Good suggestion on the AC Delco dist cap.
That proves the idea that OEM dealer parts only hurt one time while cheap after market stuff may hurt many times.
And remember them AC-delco spark plugs when you replace the plugs.
MT

i have read some tb's on the hi-voltage wire distribution and it seems to be a common problem with these vans, considering that there is no room under the top inside engine cover - some call it dog house, the manuf engineers say that all wires must run under all obstacles/guides to prevent arcing, and the caps proximity is so close to the cover which in turn is covered in tin aluminum (grounded of course) for heat reflection. Hmm - a leaky cap can definitly cause intermittent spark jump. Ya i did definitly think of that, but i did try a new gm cap and with no success. And definitly you can tell a miss under load, but this thing never misses under load - just easy cruise or easy accel.

i have read some tb's on the hi-voltage wire distribution and it seems to be a common problem with these vans, considering that there is no room under the top inside engine cover - some call it dog house, the manuf engineers say that all wires must run under all obstacles/guides to prevent arcing, and the caps proximity is so close to the cover which in turn is covered in tin aluminum (grounded of course) for heat reflection. Hmm - a leaky cap can definitly cause intermittent spark jump. Ya i did definitly think of that, but i did try a new gm cap and with no success. And definitly you can tell a miss under load, but this thing never misses under load - just easy cruise or easy accel.well i would try to back to the mapp sensor air control or check your aircleaner and lines of air flow maybe a mouse built a nest in the tunnel up front its worth a check for me what i ended up doing was putting in top dollar fuel and putting a edelbrock performance air cleaner on and thats all it took

When you purchased the AC/Delco cap did you also get an AC/delco rotor? There is a huge difference between AC/delco rotors and aftermarket ones..... I know, I fought the problem for 3 days before I replaced my one month old aftermarket cap and rotor with an AC/delco from the dealer and mysteriously away went the problem...

I did all of the plug wire re-routing to keep them away from the underside of the doghouse, changed all of the same parts Andre L did. The AC Delco cap and rotor was the only thing that solved the problem. I have a friend who had the same van (bought his 3 months before I bought mine) and he had the same problem (missing on acceleration and at cruising speeds) and the same solution that I did.

You need to monitor your fuel pressure while driving. Buy a guage, remove the dog house and hook it up to the quick disconnect and take it for a drive.

New GM cap and rotor took care of my Astro's missing problems. Genuine AC Delco parts for me.