Why wont the blm's line out???

[buddrow]

The title has been my question for a few days while I tuned my friends truck. It's a 383, comp cams computer cam(dont recall the part# off hand but it's mild), polished intake/exhaust port swirl port heads, flat tops, edel tbi intake, stock 5.7 tbi and injectors/fpr, shorty headers, stock fuel pump...

So, after trying multiple bin mods to get the blm's off of 108, I decided it had to have a "mechanical" issue(since I zero'd out the idle ve cells and still dumping fuel into the intake).

Since he doesnt understand the importance of an adjustable regulator or a pressure gauge it only made my job harder. My first thought was a plugged fuel return line since the truck sat without an engine for a year and the fuel lines were open to the elements(bugs, dirt, etc). Using air pressure regulated to 20psi I blow through the return line which was free as the air we breathe so that was eliminated. So he had another tbi setting around which we slapped on and voila! BLM's went the other direction, and I was able to tune the engine to get more ideal numbers(125-132). Haven't had a chance to inspect the fuel pod yet to see where the restriction is but I will this weekend and I'll post it here.

This is for anyone who may run into a similar issue and to emphasize to the newbies that not all issues are software based. How many times have we chased a tune issue to find out its a mechanical issue? It threw me for a loop for a minute and made me look bad as a "tuner" which I disliked lol. Now my reputation is restored and work carries on.

Have a great day everyone.

Buddrow

[EagleMark]

Or was it differant size injsectors that fixed your issue?

[buddrow]

Or was it differant size injsectors that fixed your issue?

Tried several different injectors but same pod/fpr. He had originally put reman/new 7.4L injectors(low press) and when the blms were stuck at 108 and it was visually spraying excessive amounts of fuel from the injectors creating fuel splash. He replaced those with a used set of 5.7L then a new/reman set of 5.7 injectors, same blm's. These were all using the same pod/fpr. The common component was the culprit. It was somehow creating a high pressure condition that couldn't be, wouldn't be tuned out. I probably could have put 2.8L injectors on it and it would still be pig rich at idle lol. End result is the issue has been fixed, although forensics will show the root cause at a later date.

Buddrow

[brian617]

Spent 6 months going in circles on a tune for my truck only to finally figure out it was the "18psi" spring that was coil bound at 17psi and causing me all kinds of grief. Moments which I regretted building my engine with aftermarket heads and larger cam all because of fuel pressure fluctuation problems causing all kinds of trouble. Here I had an engine idling at 33-35 map yet having all kinds of VE table trouble and cold start surging. Finally replaced that spring with the GM heavy spring for a nice solid 22psi with 305 injectors. Now the truck runs like it should and i'm still not done dialing my VE table.

[buddrow]

When I aquired my truck('90 stepside) it ran fine under light load but at wot it would sputter. Found the fpr was full of carbon from the crankcase vent. This was after modifying the tune several times. It was frustrating to say the least lol. After that everything fell into line with the tune and it runs pretty slick for a stock engine. I've been fixing cars for 20+ years and I still see new problems everyday. The fun never ends.