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Thinking of doing the unthinkable... *Rotor to cap gap. Normal?*

dont forget ignition module.. mine would surge and not idle good then one day took a crap on me and once it got warm would not let me give it any throttle or it would backfire
 
Just pull the egr and see if it is caked with carbon. You can work it manually with a screwdriver and see if it is closing all the way. Clean it with some carb cleaner and an air hose while you have it off. Check you Idle Air Control Valve too while your there. Use an adjustable wrench to screw it off and clean it up too. Worth a shot cause it won't cost you anything.
 
the egr is brand new also and has less then 1000 miles on it(same as the motor. And yes i pulled the IAC and cleaned it with no change. the TPS at idle is .7v i replaced it also and no change there. im going to be sorta busy today but if i get around to it i'll pull the egr and make up a block off for it.
 
After I put my Holley TBI on I ran into the same problem with surging. Turns out the TPS wasn't properly set. A reading of .7v is a little high for the TPS. What is your idle speed? The factory setting is about 600 in gear and about 750 or so in neutral, if you set it to high you can get surging. If your idle speed is a little high (about 900+ in nuetral) try backing it down a little. If it is about right, adjust the TPS to around .6v and see what happens.
 
May be leaking around the intake. If everything else is checking out, I would pull the intake and try again. Make sure you don't use the cork end gaskets, just run a good bed of RTV.
 
ye it is a stock rebuild with the exeption of the cam which id have to look up the numbers on again but i know its a good computer cam. Infact if i recall corectly i could have gotten away with one or two steps bigger of a cam. Just pulling the intake seems a little extreme i think in my case do to the fact that it runs really good so long as its not idleingand actually runs really gud at idle after coming to a stop for about 30-45 seconds before it starts to surge.
 
heres cam specs
Basic Operating RPM Range: Idle-5,500 RPM
Intake Duration at 050 inch Lift: 204
Exhaust Duration at 050 inch Lift: 214
Duration at 050 inch Lift: 204 int./214 exh.
Advertised Intake Duration: 262
Advertised Exhaust Duration: 272
Advertised Duration: 262 int./272 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.420 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.442 in.
Valve Lift with Factory Rocker Arm Ratio: 0.420 int./0.442 exh. lift
Lobe Separation (degrees): 112
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Quantity: Sold individually.

Camshaft, Hydraulic Flat Tappet, Advertised Duration 262/272, Lift .420/.442, Chevy
 
Yeah cam looks ok.

I'm not a MAP guy, but I suspect you could be looking at all these potential problems with one tool...a scanner. (or winaldl if you have a cable and laptop)

For one, it might be nice to know what MAP voltage SHOULD be at idle, and what you've got. That will show a problem with vacuum or the MAP/wiring right there. Autozone supposedly will let you use a scanner for free. Ignore codes, look at data.

Most engines will run perfectly fine with a vacuum leak, only exhibiting symptoms at idle.

Not saying it's *your* problem, but in general, assuming no vacuum leak because it runs fine off idle is not wise.

Clear the EGR code by removing the fuse in the engine bay (Or wherever the ECM fuse is on a TBI truck) for 10 seconds, then replace.

ECM test is essentially if the check engine light comes on when the key is turned to run. Doesn't mean it's good, that's the indication that the ECM is at least partially working though. Doubt that's your problem.
 
I really need to find out how to test that(the map) without a scanner. Becasue the scanner ive been using(auto X-ray 6000) does not give me MAP values. But thanks for clearing up the fact that vehicles with vacume leaks can run good while cruising, i didnt know that.

So in that case the to do list is as follows;

Check under cap and rotor for any cracking(i assume its the pickup that i should be looking at)

Pull off the egr and check it out and possibly make a block off plate.

Find out what my map values should be and how to test them.

And find out if theres a way to test ignition module and test it.

Also maybe do another round of carb clean around the intake.
 
Check out my thread titled with something like "troubleshooting" and the requisite links for TBI/TPI related to MAP codes. I know I've seen the voltage given for certain conditions in GM print before, and I'd have to imagine there is some way that you can check voltage with a meter.

I'm surprised the xray doesn't do MAP voltage, I'd think that to be critical. My XP240 (much older than yours I assume) does MAF gms/sec, which I just ASSuMEd meant on a MAP vehicle the voltages or pressure would be given. Very odd.

Any of the datalogging TBI/TBI folks here care to comment if this info is shown in tunerpro or winALDL?

Another thing, if TPS voltage is out of spec, (indicating higher than normal idle throttle position) and it's a "non-adjustable" TPS, that SHOULD mean the idle stop screw is too far in. If you change/d the stop screw position to correct TPS voltage, doing the "IAC reset" procedure would be the next step.
 
If you have a scanner you can watch the O2 sensor numbers to see if it is running lean or not. If you have a vacum leak it will show lean. Looking at your cam specs I think that is not a Map sensor friendly cam. I would do one more simple check. Go to auto zone and buy a $15 vaccum guage. Put a "T" in the vacum line going to the Map sensor. Connect your temporary guage to the "T" and read the amount of vaccum going to the Map sensor. Let us know how much vacum it is pulling.
 
Have a vac guage hooked up on it right now. I for get what the actual reading was(like 20-22 IIRC) but it was in the "green" zone. But inorder to get it in the "green" zone i have to have the base timing bumped up to like 4*. Also just an FYI i have tried moving the vac line for the map to diffrent ports on the manifold with no change.

And i will do a search now for the trouble shooting page.
 
Will your scan tool give "INT" and "BLM" numbers, or long term and short term fuel numbers? If so please post them, sounds like the computer has the adaptives maxed one way or the other. It's kinda hard to diagnose these kind of problems on a message board but some adaptive information while it is acting up will go a long way for me to understand what the cause is. The more scan tool info the better.
BTW are you running headers? Is the oxygen sensor mounted in the manifold or farther downstream? It almost seems the sensor is getting cold at idle, getting sluggish and causing the computer to go full lean. I don't know why but these old TBI computers go lean when the oxygen sensor gets sluggish. If the sensor is in the stock location try replacing it with known good one, make sure those threads are rust free as well, that sensor grounds through the threads. If all else fails try swapping a heated sensor.
I seriously doubt the MAP is causing problems because it would cause problems all the time not 30 seconds after going to idle. (usually). The TPS could cause idle problems if out of adjustment but is unlikely, just make sure it reads under about 0.70 volts at idle. A broken magnet in the distributor could cause idle problems as well but I think you've already checked that. Don't be afraid to set the base timing at 4-6 degrees, it will definitely help the power and drivability.
 
I'm gonna second the ignition modual. Mine idled like crap, but ran like a top under load. Rebuilt the distributor, idles great (except for that pesky exhaust leak). Try it. Summitt sells rebuild kits fo rlike 50 bucks.
 
A broken magnet in the distributor could cause idle problems as well but I think you've already checked that
Click to expand...

I have not checked that yet. Are you refering to the sort of "tone ring" thing on the dist shaft it self? I mase a post a wile back with all the numbers form the tool i'll find them in a inute and post them up. Just another bit of info that might help diagnose the problem: When i had the dist out i cleaned the balse that the module mounts to (under the rotor) with i think brake clean IIRC. Would that have been a bad move? And i get a discount up at a local parts store so an o2 sensor(the unit ment to go on my truck) is like $12 so maybe i'll just go get another one of those and a module and see what happens... I have tomorrow off so be lookiing for updates from me

BTW thanks ALOT for the help i really hope i can get this all squared away with out resorting to taking it to a mechanic.
 
I'd really NOT suspect the O2 sensor. Cruising around ok, then getting worse from SITTING would indicate (but not prove) the O2 is good. O2's tend to cool off at idle enough to not operate correctly, which would mean open loop, and the O2 is not referenced then.

On top of that, unless you can get a Delco for $12, don't think of it as a good deal. Bosch O2's have a bad reputation for a reason.

Cold start, problem exists or no?

If you wanna go through the ignition, here is a thread. Trickster has two pages posted:
http://www.thirdgen.org/techboard/tpi/238900-ignition-module.html?highlight=pickup+coil+test

As well, here is what GM has to say about this problem in regards to possible causes:
Ignition timing
P/N switch circuit
Leaking injector(s)
IAC
Sticking or binding throttle shaft (incorrect TPS voltage)
Vacuum leaks
EGR on
Bad battery cables or ground straps (erratic voltage)
AC request
MAP sensor
AC pressure too high (not sure if that applies to trucks)
PCV valve bad
Compression
O2 sensor (will result in "severe driveability problem")
 
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