94 chev van , no power , lousy gas milage

Have you checked for exhaust restriction?
Try cleaning the MAF

no cat converter , it was removed and has test pipe installed permanently....no maf but it does have a map sensor...map sensor output checks out , shows 5 volt peak

Mechanical and electrical side seems good.

Though fuel pressure is correct, there could be restricctions causing insufficient flow during acceleration. Have you tested the operating pressure during acceleration?

one thing i should have mentioned right at the start was this thing pings when you try to make it climb a hill;;;in the old hei distributor days i would have simply bumped the timing back a little till it stopped but i have no clue on this computer controlled truck...like i said , i should have mentioned it right away ...

You can't do anything with the ignition timing as it is computer controlled and you have replaced the knock sensor so this pinging is strange.

Here are the diagnostic aids from the shop manual, see if it is of any help.

LACK OF POWER OR SLUGGISH

Symptom Definition

Engine delivers less power than expected. Little or no increase in speed when accelerator is applied.

Possible Causes & Corrections:

Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter.

Check engine valve timing and compression.

Check engine for a worn camshaft.

Check TCC system for proper operation.

Check transmission shift pattern and downshift operation.

Using Spark Tester (ST-125), check for adequate spark output.

Ensure initial ignition timing is properly set.

Check ESC system for excessive retard.

Check EST system for proper operation.

Check air filter and fuel filter. Replace if necessary.

Ensure fuel system pressure is correct at all engine speeds.

Check for poor fuel quality or water-contaminated fuel.

Check injector wires for short to ground at air cleaner.

Check for spray from one injector on TBI unit. Malfunction may be present in injector assembly or in signal to injector assembly. Isolate malfunction by switching injector connectors. If problem remains with original injector, injector is defective. If malfunction moves with injector connector, problem is an improper signal in injector circuits.

Check PCM grounds. Ensure they are clean, tight and properly located.

Ensure EGR valve is not always open.

Check charging system output. Repair if output is less than 9 volts or more than 16 volts.

Check A/C for proper operation.

other than the knock sensor and map, what does the computer look at to set the timing...........

TPS, VSS and transmission signals.

i replaced the throttle ps with a new acdelco one , no difference....the speedometer reads correctly and has no problems....does this mean the vss is not a problem and what or how do i check the transmission signals john b

If the transmission is shifting correctly and you have no trouble codes, that would rule that out as well.

Maybe you need to look at the gas you are using. Some treatment might make a difference.

i use the same gas in my pickup,same engine [tbi 350],same transmission[700r4],same rear ratio and the pickup is a 4x4 , which means its heavier..........the pickup works like a charm and the difference in power is sustantial and there is no spark ping from the pickup....

You might have to look at the mechanical aspect of the engine. Maybe the timing chains are stretched.

Is this problem new?

easy service,mostly highway miles,41,000 miles , cant see it...........compression test ,all cyls within 5 lbs of 150 pounds..........no problem is not new but seems to be getting worse , gas milage is slipping over the last few months john b

At 41 k miles, the engine is almost new. With everything looking in order, it seems strange.

Maybe you should be looking at the fuel flow. Possibly a partially clogged filter?

first thing i did was a new filter.....flow test ,as i remember,was a pint in about 12 secs john b

also , when climbing a hill it downshifts as it losses speed...in the lower gears the engine revs up and it will start to regain speed.........if the fuel flow was restricted , would it be able to rev the engine up............

It would depend on how bad the restriction is.

is there a spec for fuel flow. john b

I am running out of ideas. Are the spark plugs running clean?

slight fouling in #3 cyl,now and 10,000 miles ago when i installed new acdelco plugs...no real buildup , compression 150 lbs + or - 5 on all cylinders....engine as smooth as silk

I could not find any reference to fule flow amount, only pressure specs of which yours is correct.

i am still inclined to think the spark ping on hills is a clue , mostly because the other tbi truck does not ping

I agree with that but what is causing it? Timing out of sync? Excessive carbon in cylinders?

any way to check the Timing out of sync theory without dismantelling the engine

No, you would at least have to remove the covers.

took this thing out yesterday with an old auto xray scanner hooked up to moniter as i drove..went about 8 miles to warm it up to a long hill that the vehicle does not like to climb.....as usual it pinged loudly as soon as the hill slowed it down........what i found interesting is that the knock sensor showed 0 response and the knock retard showed 0 degrees..........other readings were coolant temp 194.9,engine run time 1800 secs,egr cycle0% ,ccp duty cycle 0%,ccp purge off,idle kicker 0

the retard and egr do not appear as they should.....does this information shed any light on the problem

The ECU does not seem to be responding to conditions and maybe it is the one at fault. ECU can fail over time due to bad capacitors. If you can get you hand on an ECU, give it a try.

ok , probably take couple of days to get one with the same number..

Good luck.

any trick to replacing it , do i just unplug the old one and plug in a new one....do i have to take the battery cable off or anything else ....

Disconnect the battery negative terminal first.

ok , i have a used computer complete , correct number , from a 94 s10.....do i have to change the prom anything else before i install it ....this is a conversion van with the computer located behind the b pillar

Disconnect the battery negative terminal. Disconnect PCM. Reinstall new unit. Reverse procedures for installation.
Run vehicle to let the PCM relearn.

wow , you guys are fast...will do tomarrow and let you know what happens

installed replacement pcm...ran about 20 miles , non highway,about 45 mph.........did notice difference...spark retard showed up to 5 degrees retard and showing activity on knock sensor...feels smoother...but the service engine light is on and no codes....should i install original prom ...

If the service light is on with no codes, it can mean the replacement PCM has a fault too. Yes, I would like you to retest the original PCM to see how it works.

do you mean the original prom?????

yes

I TRIED PUTTING THE ORIGINAL PROM IN THE S10 COMPUTER...........ALL MY PROBLEMS RETURNED IMMEDIATELY.............SOOOOOOOO I PUT THE ORIGINAL COMPUTER BACK IN THE VEHICLE WITH THE S10 PROM INSTALLED....the improvements were immediate....question is what problems will it cause using a 6 cyllinder 4.3 prom in an 8 cylinder 350 van

6 and 8 cylinder don't mix. To get the engine started itself would be a miracle and to get it to run perfect, the manufacturer would like you to be in their R&D division.

it works so much better with the 6 cylinder chip............what possible damage will it do if i run it till i can get the correct prom