Hey everyone, i'm having a problem with my TPI project. It seems like it idles alright (maybe a little rough). But when i hit the gas it seems delayed and i get a "buhbuhbuhbuh" acceleration sound instead of a "varoom" sound (lol). I'm not really sure what the problem with it is. But the motor feels a little shakey when i do it, like its not firing right/smoothly.

I've checked the timing and set it to factory spec of 6 BTDC, i've checked all the cylinders for good pressure, and my fuel system seems to be working fine (all new). And i have also gone over the entire motor and checked for vacuum leaks, none are to be found.

I ordered a new ignition module and a new coil(in the mail) in hopes this will solve my problem, but was wondering if any of you have had this same problem? Any info would be great!

On a side note, i used my scanner that plugs into my ALDL, it seemed a little wierd to me, but at idle the advance is 26 degrees, and when i floor mash the throttle and let off it jumps to like 37.8 advanced. The knock sensor also seems to be counting whenver i floor it.

Please help me!

 

Im not sure what kind of car or year your TPI project is some more information would be helpfull.

Here is a idea though
There is a wire you need to unplug before you time it I believe it is called EST. That pretty much disables the computer from advancing the timing when you time it. Otherwise you could be about 26 degrees off.

 

Yah, i unhooked that like my guide says so the computer wasnt adjusting the timing on me when i set the 6BTDC. It's an 87 305 TPI setup, so its MAF, i literally pulled the motor out of a camaro and dropped it directly into the blazer(with the help of painless wiring harness and other parts).

 

Did you swap the ECMs, or at least the EPROMs if the ECMs part#s are the same? I doubt the Blazer had a TPI in it so the EPROM would be different, more so if the Camaro had the Cold Start injector.

 

oh yah, i swapped the ECM from the camaro in ( im sure it wouldnt even run on the blazer computer) i'm using the stock chip and everything in it also

 

I am going to assume that the Blazer is one of the older ones, not the newer ones. If so, i am going to guess that it was orginally TBI. So, i will base my assumptions off of these and with that being said, here is my take:

I will bet your problem is in the fuel delivery. What pump are you using?

 

I Put one in my 1992 Chevy Blazer. I did change out my fuel pump. The stock fuel pump should be good for a stock 305/350 TPI. Are all your sensors reading correctly when you hook it up to the ALDL?

 

yes, my blazer is an 86, which actually came with a stock ole on-the-block fuel pump. I have an accel high pressure fuel pump in-line, its rated for up to 50psi i think and up to 400hp.

All my sensors seem to be fine, no codes or anything which is wierd, still waiting for the ignition pieces though.

Isnt 26 degrees at idle a lot of advance though?

 

Oh, now that i re-read it, now i see wha tyou are saying. I misunderstood, sorry about that.

Hmmm. I'm thinking.

The only thing i am unclear with is you say you set the timing to 6° BTDC. Then you say at idle it has 26° advance. You give 3 different timing specs. For certain, what is the initial timing and what is the total timng?

 

Well mechanically, when i unhook the ECM from the distributor, and i set the timing, i set it to 6 BTDC. Now once i plug it all back in, and i'm letting the truck idle, i check my scanner tool, which says "Spark advance" and it reads 26 degrees while at idle, then i floorboard it, it goes up to 37.8 (total timing i think?).

So does this mean my computer is adding 20 degrees of timing at idle?

 

Yep, that's what it means. Maybe a shade high, my 91 305 Formula ran about 20-23 BTDC at idle. Check the fuel pressure. Set it to approx. 43 PSI with the vacuum line to the TPI regulator disconnected and plugged, then see what it runs at when you reconnect the vacuum line.

 

I finally got to wiring my fuel pressure gauge, and the pressure seems to be good, right around 43-44 at idle, and when i floor it, the pressure climbs a little bit, but not above 50.

But i think i found the problem! Today i pulled all my plugs to see how they were doing, most of the plugs were ugly (prolly from all the idling i've been doing) but one plug was practically spotless, in fact it looked as if it hadnt even been run! So i'm thinking i've got a bad wire to that cylinder, hence the reason its so clean.

Off to the store tommorow to buy new plugs/wires, wish me luck!

 

Well, i changed out the plug/plug wire on the cylinder and i still dont have a solution. So now i'm really starting to think that maybe that injector isnt firing or is clogged, is there any way i can test this without taking the entire system off the engine?

 

Did you drive it yet? Are any of your header tubes glowing?

I just finished a TPI swap on my '88 SS, and drove it about 75 miles so far with no trouble at all. Tonight it started doing the same thing you're describing, (stumble off-idle, but smooths out a bit once over 3K rpms) but I noticed either my #4 or #6 header tube was glowing when I parked the car tonight. I'm going to borrow a noid light from my mechanic tomorrow, but I'm also going to check the plugs and wires. Maybe one of them is crispy on the header.

Keep us posted please!

 

well just a side note if your header is glowing your running too lean

 

If it's glowing, its running rich. That's unburnt fuel getting ignited off the heat of the headers.

It could also be an extreme lean condition, like above.

Timing that is too far retarded can also cause glowing. Again, same thing. Unburnt fuel getting ignited off the heat of the headers.

If its just one, i would look to a clogged injector. Also, yanking the plug can tell a lot, too.

 

"Aquikgmc" wrote:
and
The ECM is programmed for a specific fuel pump curve. Aftermarket high pressure fuel pump curves are different, adjustable fuel pressure regulators are required to set them to to factory specs (43 psi @ no vacuum.)

You're engine should idle at 36-38psi of fuel pressure. There's always some differences even in identical OEM parts so, the ECM also controls the fuel pump voltage to compensate for those differences. I assume you're using the Camaro's fuel pump circuit to run the Accel pump.

 

yah, im using the fuel pump relay and all of that out of the camaro.

Like i said earlier though, the fact that 1 out of 8 plugs is practically spotless like it hasnt been run, even with spark makes me think that its sparking fine, but there isnt any fuel being squirted in that hole.

 

YES! Just wanted to give you all an updated, pulled apart the system tonight at the shop, pulled off the throttle body, the plenum, and one of the runners, the injector in question was NASTY. Changed it out with another injector i have, put it all back together, and it purrs like a kitten! I am very suprised how that little 305 TPI runs, thanks for all the info! This site is the best

 

Glad you got it running. How's the knock sensor doing? I'd like to know what the O2 sensor is doing with 7psi of fuel pressure over spec (36+7=43psi) at idle.

 

Thats so wierd, everywhere i have read says 42-43 lbs is perfect for the fuel system. The stock regulator will only let that amount in right? isnt that what the return line is for? If its a little over i'm not too worried much right now, on the FAQ page it shows that more pressure=more power/torque. I'll let you know when i check it this afternoon though.

 

For a stock pump, and regulator, yes.

ALLDATA specs the fuel pressure with ignition on/engine off at 40.5-to-47psi, and 30.5-to-44psi at idle for all 85'-90' 5.0L/305s, and 86'-90' 5.7L/350s except DOHC.

I use the median of the minimum and maximum. after I stroked it my builder recommended installing a high performance pump & adjustable regulator, and set it for 38psi with key on/engine off, then add, or subtract pressure to fine tune.

Vacuum determines the fuel pressure at idle (around 15in Hg depending on how many vacuum assisted devices you have,) the higher the vacuum the lower the pressure, so if your vacuum is abnormally low at idle the fuel pressure will be abnormally high.

From "Walbro Performance Fuel Pumps"
Especially if you have larger than stock injectors, like you said, don't need to worry about it now. I did because I've increased the air flow, added 30# injectors, and headers.