Tuned Port problems.

[Okiedokie]

The TPI 350 Chevy motor is having an irregular starting issue as I begin to work the bugs out of a new build. One time it starts immediatly, next time maybe take several minutes of cranking on and off to fire. I can drive it a few miles, then shut it off, and some times it fires right up, often it does not. This is my first experience with a computer in a hotrod, and I am beginning to long for a carb. Anyone have a thought about where I might look. The fuel pressure remains at 45psi on the gauge.

[WZ JUNK]

The TPI 350 Chevy motor is having an irregular starting issue as I begin to work the bugs out of a new build. One time it starts immediatly, next time maybe take several minutes of cranking on and off to fire. I can drive it a few miles, then shut it off, and some times it fires right up, often it does not. This is my first experience with a computer in a hotrod, and I am beginning to long for a carb. Anyone have a thought about where I might look. The fuel pressure remains at 45psi on the gauge.

I have a book on TPI by Choco Munday (sp), who use to post here on the rrt.  I will try to remember to have a look at it tomorrow to see if says anything about your problem.

John

[Learpilot]

The TPI 350 Chevy motor is having an irregular starting issue as I begin to work the bugs out of a new build. One time it starts immediatly, next time maybe take several minutes of cranking on and off to fire. I can drive it a few miles, then shut it off, and some times it fires right up, often it does not. This is my first experience with a computer in a hotrod, and I am beginning to long for a carb. Anyone have a thought about where I might look. The fuel pressure remains at 45psi on the gauge.

I had problem with a tpi starting. It was an early one with the ninth injector. That was the problem. The start ninth injector was worknig sometimes. I replaced it and the problem went away. If you have a late tpi you will not have the ninth injector, and I do not know what it is. Does the engine run ok after it starts ?
That is just my experience, I am no EXPERT !
Rick

[Okiedokie]

Thanks John and Rick. Yes it runs fine once it is running. It is a late TPI with no ninth injector. I have a scan tool and it shows no codes and all seems to be in spec. I must be overlooking something.

[wayne petty]

does your scan tool view live data?  print this..




these can be hard to diagnose...

i would like to know if you can see the TPS voltage...

can you verify that each time you take your foot off the gas pedal.. that the TPS voltage drops to the EXACT same voltage..  as displayed on the scan tool...

if it varied. or rises above i seem to recall  0.45 volts.  the ecm thinks you have your foot on the gas and it turns on the clear flood mode.. shutting down the injector pulse width to almost 0..

do you have a fuel injector test extension? you can build one if you have a junk yard near by..   fuel injector connectors can be had from many cars..   but the other side is harder to find.. look in saabs and volvos..  you will find some of the oxygen sensors and some of the abs wheel sensors have the same connector as a fuel injector has..

you can slip this test lead in.. using female insulated bullet connectors to join each  of the 2 wires...  this allows you to grab into one side or the other and look at the fuel injector pulse width with a digital volt meter.. using the MS scale that some have..   MS is millisecond..  engine running fully warmed up..  the injector pulse width is usually 1.3 to 1.4MS..

some scan tools will display this ms injector pulse width..

it may also show clear flood or cranking..

post what year you think your fuel injection is..

[Okiedokie]

Thanks Wayne. Yes my scan tool displays live info. I will use your tips and report back my results.

[WZ JUNK]

I looked at Choco's book this morning and I did not find anything that would help you, but it is a great book.  

I had a problem like yours several years back and it was caused by a bad ground.  The engine would fail to start occasionally and sometimes it would just quit while driving.  It was difficult to find the cause but one day I was messing with it and I noticed a loose bolt that held a ground wire and when I tightened the bolt, it solved the problem.  I hope your problem is as simple to fix.

So my only advise is to check the grounds and if you do not already have the engine grounded to the frame or battery, do so.

John

[Okiedokie]

I will double check all grounds. Since it has not quit while driving that seems dubious, but you never know. Thanks for your input. Joe

[wayne petty]

lets talk about grounds....

take it to the dirt...


electrons flow from Negative to positive...


if you don't have good grounds between parts..    when electrons are products.. or used...  if the grounds are bad.. there will be differences in voltage on those parts...

the battery negative has 2 wires from the top of the cable... a thick one to the engine... a thinner one.. usually 10 gauge to the body...

this connects the engine to the battery...

the smaller one connects the body to the battery...

there also has to be a ground connection between the engine and the body.. usually at the firewall..  why...

electrons like to take the shortest path...

since the dash board gauges are hooked to the engine with ONLY ONE wire..  without the ground.. the electrons have to run up the battery negative cable to the smaller cable to the core support then all the way through the body to the dashboard support... where a ground wire is attached to the instrument cluster voltage regulator ground and for the dash lights ground..

now.. the alternator also puts out electrons on the negative side..

with weak or missing grounds...  with the alternator charging.. it can put out significant more voltage in the engine block than there is flowing to the body...

the voltage drop test i posted...  1.2,3,4.. i had a chevy pickup that acted crazy... one test 4 i got 8.5 volts..  yes.. between the engine and the body was 8 and a half volts difference..


now... i have to explain..  that the Engine control computer is ONLY grounded in most cases to the ENGINE.. not the body...

so if you have a difference like what i measured..  you will have nothing but problems..


let me try to clarify the issue even more..

when you use a digital volt meter.  you are measuring the difference in voltage between the two places you touch...

with the engine running and the headlights on...  there should be current moving through the wires..    if you test where the 2 wires are connected to .. you will see a slight voltage drop as the copper wire has resistance..

this is why you use the 2 volt or the millivolt setting if you get a 0.00 reading at the 20 volt DC setting..

this is just to verify the wiring is working as designed...


follow the wiring harness from the ECM..   you will find several wires that connect to ground..   if you don't know what year your system is..

please post the number off the ECM.. and the prom code.. the prom number is viewable with a scan tool.. it will be a 4 digit number..

if your computer is mounted inside the car/truck, wiring through the firewall. the ECM ground is probably on the back of the heads..

if your ECM is mounted under the hood...  a 4 connector PCM..  the ECM ground is probably on the drivers side of the block just above the oil filter..

since this is a transplant...  or it seems to be.. do you have unswitched fused power to the proper wire on the ECM.. and switched fused power..

sometimes if you don't have UNSWITCHED power to keep the computer active when the key is off..  it won't keep the memory.. and it won't be able to retract the idle air control motor for the engine to start easily..

[Okiedokie]

Just an update. I had taken the 40 to a friends shop for a hood repaint and some touchup of assembly "oops". He has had a family interuption so it will not be back in my shop untill early next week. I will then bega=in to use your tips. Joe

[Okiedokie]

Wayne, the only readings that varied out of the data values on your info were the inj pulse width at 3.335 and the block learn at 112. Your thoughts? Joe

[wayne petty]

those readings are way off..

3.33MS injector pulse width tells me there is a serious problem someplace..

at idle.. warmed up i expect 1.3 or 1.4MS..



could you check the fuel pressure with a gauge???    38/39 PSI.. engine idling..  as i recall.   and it should hold for several minutes after shutting off..    probably not dropping below 20 pounds pressure for 10 minutes after shut off.. ..     low fuel pressure will cause a wide injector pulse as the computer is trying to keep the engine running..  

does this engine have an air injection system into the exhaust???  

where are the oxygen sensors.. i am taking that this is a swapped in motor..


were you able to write down the sensor values cold.. key on engine off..

TPS..  throttle closed________________..  throttle wide open.______________

coolant temp sensor..   engine cold..____________  engine hot__________ verified with a infrared temp gun if you think it's not even close...

MAP   manifold vacuum.. engine off.._______________   engine on.. ___________

if equipped  MAF...   idle should be like 6 grams per second. or point 6.

air temp sensor.. cold  __________  running______________  .


can you check the oxygen sensor voltages.. see if they are switching..    0.1 to 0.9..    not beyond that..     how many cross counts at 2500 RPMs as shown on the scan tool.??

IAC at idle..   idle air counts..    i like to see 20 to 50 at idle..   what do you have at idle???

does this engine have a small cap HEI...   if so.. would it be possible to pull the cap and the rotor .. look straight down at the distributer shaft..  there will be a riveted on reluctor around the shaft.. you can see through the opening in the center. the exposed second layer.. a magnet.. are any cracks visible?  if so..   replace with a reman from autozone..  it will have a different style of pick up coil and a totally different solid reluctor that works far better..
its a cardone reman... usually labeled at oem reman..  the cracks in the magnet effect electronic spark timing..  seriously.. and throw the computer into a tizzy..



where is you base timing set to    with the distributer cap off..  bring the crank around in normal rotation until the damper timing mark is lined up with the timing pointer at where ever the factor spec is..   see if the tips of the reluctor line up perfectly with the tips of the pick up coil...      or you can note which way the rotor is pointing toward the number one or number 6 wire in the cap.. and slowly turn the crank till its pointing in those directions and the reluctor and the pick up coil line up perfectly..   then look at the crank timing marks..    since i don't recall if you mentioned what year the engine and fuel system was from.. i cannot tell you what the base timing should be..    0...8 before .. 10 before  15 before???

the more info i have.. the less guessing i am going to have to do..

i seem to be pretty good at guessing..  so i will be here awaiting you to set on the scale..

guess your weight for a buck..!!! or something like that..   except the prize is a car that runs properly..

[40_Tudor]

I have an 87 5L TPI in my Forty. Had trouble starting when I first put it together. When I first got it running I had an in-line pump in it that I had to key many times before it built enough pressure to start and run. I installed a pump in the tank and that cured the hard start problem. I bought a plug from Street and Performance to eliminate the 9th injector and they burnt a chip foe me so it would add extra fuel through all injectors on start up.  It starts right away know, unless it sets for an extended time, then I have to key it a few times to bring the pressure up then it fires right up. Check the specs for the fuel pressure, my 87 is 60psi. Check out Street and Performance, http://www.hotrodlane.cc. They have the answer for about any fuel injection problem there is. They have CD's on installing TPI and on-line videos. You can also call them and describe your problem and they will probably tell you cure the first time. They have been installing fuel injected engines in street rods and muscle cars since they first came out.
I have over 9K on the set up and no problems yet.
Hope this helps. Good luck.

Joe

[Okiedokie]

Thanks for your input Joe. I am familiar with S&P and their site. I do have an in-tank pump and the TPI is off a 90 IROC, so no cold start injector. Several acquaintances around here have hauled their TPI cars to S&P for setup. I am just not ready to do that yet. I would like to learn enought to do it myself. If I can???

So now I have gone back to the beginning and reset everything by the book. I set the timing to 10 btc with the set timing connector disconnected, the base idle to 500rpm [it was not a smooth idle] with the factory proceedure with the IAC disconnected etc, and set the TPS at .50. Then I could not get it to start and idle, I could keep it running at about 1200 rpm, but not idle. I then turned the idle screw in about 1/2 to 3/4 turn, and then it will idle at about 900 rpm, with some surging between 750 and 900 rpm's. Even though the temp on the scan tool showed 190, it remained in open loop. I think it should have been in closed loop at that point? Hopefully Wayne will chime in and advise me further, I hope. What a resource Wayne is. Joe

[wayne petty]

TPS voltage at idle has to be at like  0.35..  or it will fall into clear flood mode..

engine off.. please work the throttle several times..  to verify that the tps voltage come back to the exact same fraction of a volt each time..

if it changes..  you have a worn throttle shaft bore..

TPS throttle closed.... 0.35 volts...
TPS  engine off wide open.. about 4.5 volts.

now.. warmed up.. with the TPS at 0.35 volts.. what are your IAC. idle air counts..    i like to see 20 to 50 IAC.. at 475 to 550 RPMs.. .

the idle air counts are the stepper motor position of the idle air motor.. base idle has to be done with the idle air motor passage plugged ..  

if your idle air counts are lower than 20.. the ecm is trying to slow the engine down farther..  open the throttle slightly with the screw..

  if higher than 50.. and the engine is warmed up..  the throttle plates are too far closed and the ecm is trying to make the engine idle..

changing the throttle position.. requires resetting the TPS.. to keep the voltage at 0.35 volts  at idle..


did i send you a pm with the TPI starting strategy??  


i will be around playing with the 4180 holley on my van if you want to call and talk about this.. .  you have the number..