I just put a TPI into a 95 Tahoe(I know, NOT a 3rd gen). It's a Vortec headed 355 around 9.7:1 compression, 305 Tpi roller cam w/ 1.6 roller rockers, ported heads(bowls and exhaust ports), fully ported plenum and ported base. It has 305 injectors and a stock chip/tune(MASS). The set-up is more for economy and throttle response in a daily driver/mud play 4x4. Its running rich at idle(black haze out tail pipes) and then stumbles/backfires through the exhaust at around 4k, smooth otherwise. - It's got a new acdelco fuel pump, the regulator is clean and holds vaccum, new wires, new cap/rotor, new coil, new plugs spec for 97' truck(vortec heads), and new acdelco O2. - It's not throwing any codes. I've tried 2 TPS sensors, 2 ignition modules, 2 coils, 2 sets of wires, timing ranging from 6-12 (base) to EST unhooked. It's holding between 13-15in vaccum @ idle goes over 20 w/ throttle. I have to get a fuel pressure gauge to check pressure, but if it's low, why do I have a rich idle? The injectors range from 16.7 to 18.8 ohms, 4 being around 16.7, 4 around 18.7. I've searched and maybe the 18's are to high? I even re-set the valves to the point that a couple rattled on start up. - I'm lost. Any help would be greatly appreciated.

later, justin...

 

I change the ECU and it seemed to solve it, but it threw an SES. It had developed a miss-fire(re-squeezed all plug wires), which smoothed it back out at idle, but now it's poping and stumbling again! - I'm going to go check to see what code is present. it's still really rich. I checked the autolite book which calls for 26's factory in a TPI car and the 605's in the vortec heads. They spec to be the same heat range.

- anyone?......

 

I'd try getting a replacement O2 sensor, just to eliminate the possibility of a faulty new one....

 

I'm gonna try that and another new CTS. - now its starting hard, and stumbling anything off idle......

 

Mine was running real ruff and wouldnt rev past 4k due to my o2 sensor backing out so it could be that. Make sure its hooked up and the wire is not burnt or anything.

 

Could be high fuel pressure. With too rich of a mixture, an engine will not want to rev high. It's called rich misfire. When that happens, can you see black smoke out the tailpipe? The ECU is probably able to compensate enough to make smooth driving at medium loads, but not when PE is on at full throttle - that commands a rich mixture, and combined with really high pressure can get you into the rich misfire region. Backfiring out the exhaust sounds like there's fuel and air getting there, which supports what I'm saying. Intake backfires are generally a lean indicator.

Could be a regulator problem or a blocked return line.

 

I think my biggest issue is the rich situation. I got a new pigtail for the CTS, due to my old one being basically just two metal prongs. - The O2 is a brand new acdelco unit, and the wire is fine. Wouldn't the computer throw an O2 code if it were screwed up? I'm going to pull the fuel rails, leaving the injectors attached (9th included) and jump the fuel pump. This way I'll know if any are bleeding by. I'll blow out the return line while I'm there. -

- It threw code 33 and 42. I had brought timing up due to the new found start issue + the rich issue. I had it at 8 base(EST unhooked), but it wouldn't even idle w/o the EST hooked up. I figured the balancer had slipped, throwing my figures off. Now that it has a code 33 I'm going to check the TPS adjustment, reset the IAC and go from there.

- this thing is drivin' me friggin nuts....

 

Thanks for the suggests...keep 'em coming...

is there anyway to test an o2 sensor?

later, justin...

 

Yeah, when warmed up, and if it's rich, the volts should be 0.6V-1V. Probably closer to 1V in your case.

In closed loop, it should switch from less than .3 V to greater than .6 V and back and forth continuously quickly.

At full throttle, should be greater than .6V.

If your O2 is working, and you want to tell if your 4000RPM problem is rich or lean, just measure the O2 volts. High is rich. But, be careful, if it's misfiring, it will throw a lot of air at the sensor and it will read lean.

 

You have headers and exhaust mods, right? Too much Backpressure can cause stumbling and backfiring at high rpms.

Have you tried a new or rebuilt distributer?

Does it have new valve springs?

Doesn't sound like a lot of vacuum for a 305 TPI camshaft.

Just some ideas.
I recall someone on this board a while back having some rich condition issues with his injectors and fuel in the exhaust. Might do some searches and see what his solution ultimately was...

 

exhuast - headers, all mandrel 2.5 duals, hooker maxflows -

- I'm not sure about the vac. Seemed good to me, but I'm used-to my cam(sig). It does have 1.6 roller rockers though...

- It has the Lt1/Z28 .510 lift valve springs, and they're brand new.

- Haven't tried a dist...yet...has no slack...2 different modules. -

Its' just wayyyyyyy to rich. I'm sure that the issue, but I'm not sure why its rich. The coolant temp sensor ohms are good, and I've got 5VDC to one side. - Could crossing the two wires to the CTS make it not operate properly? - I just put on a new plug in(old one falling apart) and I think I crossed the wires(new one not colored wires)...

later, justin...

 

Pulled fuel rails/ injectors. Held all up in air, 9th included, and jumped fuel pump. No leaks, wet. Tried w/ key on and off. No difference. - going to test O2 voltage...

 

O2 sensor reading just kept climbing. I let it run about 5 min. It got to .8+ vdc...why won't it lean out? The motor runs a couple minutes, then changes sound(closed loop I believe). But the O2 keeps climbing. It's already killed a set of autolite platinum plugs, and I haven't even driven it except down the street once. MASS sensor? - no codes.... It idles smooth, and sound good now, but it won't lean out....

 

Well, the O2 sensor is working fine. The ECU just can't remove enough fuel to get it to switch. Some thing like too much fuel pressure is probably causing your problem. Maybe a bad regulator, or blocked return line. It could be the MAF too, but it's expensive to just replace that without testing the other things first.

 

Fuel press reg holds over 10 vac on vaccum pump. - Blew through return line while I had the plenum off checking the injectors...right to tank, no restriction. Stock fuel reg. took apart and checked, looked good, still held better than 10 in vac. - CTS ohms good, has 5 volts to plug. I guess I've got to get my diag plug-in wired so I can hook my scan tool up.

- also, a buddy of mine works for Tropical International(Acdelco parts warehouse) - I can "borrow" a MASS to see if thats my issue...

 

I don't have a fuel pressure gauge, or I'd check it... - I'm gonna unhook the 9th injector and see what that does. It's got a new delco cold start switch(intake sensor) but who knows...


very much, but unfortunately I'm still lost...

 

Unhooked 9th - no difference. I may have found my issue though...

I just found out("search" is so much fun) that the ecm I'm using is the 85 set-up, not the 86 that I thought. Meaning it is the "87" not the "165". - All of which I understand to mean that I have the MAS module instead of the two relays(MAF power/burn-off). - This much I know from the fact that I have that box, and I have the wierd prom ecu. I guess I'll be re-wiring a bunch tomorrow to switch to the two relays instead of the MAS box. - I have an 87 ecu to use, but I WAS keeping my TPI systems(I have 3 complete, 1 parts) together. -

Does explain why the 87 ecm threw a code when I tried it and the current one never has.

later, justin...

 

To all those who help/suggested,

Seems like it's fixed. I'll know more as soon as the charger brings the battery back up a bit(hood light, interior lights, cooling fans jumpered, etc...all day). I did the 87 ECM swap. Re-pinned and wired in 2 relays for MAF and for Burn-off. Fired right up, idled high(leaned out...FINALLY!!!) and the O2 readings stayed around .4 volts....I just switched the plugs again. I had put in some standard autolite 26's to figure it out because of the cost of the proper plugs for the Vortec heads. I'm going to re-set the base idle and re-adjust the TPS...Hopefully its all over

thanks again...justin

 

Great news. Now get that thing back out there on the track/street and light'em up!