another tfi question

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dgl6y6
Posts: 84
Joined: Wed Jul 22, 2009 8:56 am
Location: St. Louis

another tfi question

Postby dgl6y6 » Wed Jul 10, 2013 1:09 pm

Hey I was looking though threads and diagnostic procedures and wanted to ask everybody here
My '88 b2 died while sitting at a stop light yesterday. It cranks over but wont start. I am getting fuel but no spark. I tested the power to the coil against ground and got battery voltage on the power side and 3 volts on the tach (green) wire that goes to the tfi.(this was while the coil was still connected. when the coil is unplugged (from the 2 wire power plug), i get battery voltage between the red and green wire. the thing is I couldn't get a spark out of the coil even while cranking. I replaced the coil even though it tested good and still no spark. I know the tfis like to go out when it gets hot but i don't know if it could fail in this way. Also the coil gets hot really fast with the ignition in the run position. I'm going to scan for codes tonight.
Does this sound like a bad tfi? I couldn't find any info on one failing in this way so I'm asking if anybody has any advice.

dgl6y6
Posts: 84
Joined: Wed Jul 22, 2009 8:56 am
Location: St. Louis

Re: another tfi question

Postby dgl6y6 » Thu Jul 11, 2013 5:51 am

Update:
The TFI module was bad. I ran the resistance test and the reading between the coil negative and the hall effect ground was 0, short circuit (supposed to be 4.2 kohm)
Never heard of one failing in this way so I wanted to put this out there.
New TFI and it started right up. only problem, the new tfi is bad but in the traditional way. It works fine till it gets hot then the engine dies like turning off the key. wait for it to cool and runs again untill hot.
Thankfully the napa right down the street has another one so I will exchange it this afternoon.

BTW I used Copper anti seize between the tfi backing plate and the distributor. I know people who say this works great for computer heat sinks and it has great electrical conductivity. plus its way cheaper than thermal paste.

dgl6y6
Posts: 84
Joined: Wed Jul 22, 2009 8:56 am
Location: St. Louis

Re: another tfi question

Postby dgl6y6 » Fri Jul 12, 2013 4:50 am

Another update.

Put in the 2nd new tfi module and it still didn't start. I had spark now so i knew that the tfi was working and i had some other problem. (the first new tfi might not have been bad after all. but they swapped it for the better one so im happy). neither fuel pump was coming on. checked the relay, it was clicking on. jumpered across the relay plug and still no fuel. tried to trace the wire to the bundles in front of the drivers firewall but couldn't find the orange/light blue wire. all of the sudden the fuel pumps kicked back on. its been running great since then but now my fuel gauge isnt working. does anybody know where those wires go under the hood? I cleaned the contacts in all the plugs but its still out.

drofman
Posts: 472
Joined: Sun Dec 27, 2009 9:36 am
Location: san dirgo

Re: another tfi question

Postby drofman » Sat Jul 13, 2013 1:21 pm

You might want to check the connection at the Inertia Swt located on the pass. side towards the firewall. Sometimes they corrode at the connector. The fuel gauge is on it own circuit.

dgl6y6
Posts: 84
Joined: Wed Jul 22, 2009 8:56 am
Location: St. Louis

Re: another tfi question

Postby dgl6y6 » Tue Jul 16, 2013 4:29 am

drofman wrote:You might want to check the connection at the Inertia Swt located on the pass. side towards the firewall. Sometimes they corrode at the connector. The fuel gauge is on it own circuit.


Yeah I was aware of that. That's why I bypassed it a few years back. haha It turned out it was the in-tank fuel pump harness. I tightened up the contacts and cleaned them with a piece of 12 ga stranded wire. Good as new. I'm starting to think that maybe the first tfi wasn't bad and one of the plugs i cleaned was the culprit. (I did wiggle the fuel pump plug when trying to get it started.)
Anywho, Im convinced that first tfi had been going out for a while. It hasn't run this good in years. smoother idle, more power, I can go up hills in OD at 65 mph. Either the gauge is reading high now or I am getting really good gas mileage. 175 miles and I'm at 3/4 of a tank. The gauge goes up past the F when its full.
Last edited by dgl6y6 on Tue Jul 16, 2013 5:06 am, edited 1 time in total.

dgl6y6
Posts: 84
Joined: Wed Jul 22, 2009 8:56 am
Location: St. Louis

Re: another tfi question

Postby dgl6y6 » Tue Jul 16, 2013 5:05 am

One more thing I wanted to get out there. The first TFI I bought was the $50 one from napa. It had a circuit board inside but was hollow otherwise. the second one I got was the $90 one from napa, the one from Echlin. I had been filled and the circuits encased in some kind of epoxy making it (hopefully) much more reliable. If you ever buy one of these, get one that feels solid inside.

dgl6y6
Posts: 84
Joined: Wed Jul 22, 2009 8:56 am
Location: St. Louis

Re: another tfi question

Postby dgl6y6 » Fri Jul 19, 2013 4:37 am

So I filled up with gas and it only took 11.5 gallons. The gauge was reading just below half so I guess its correct. At 270 miles that means I'm getting around 23 mpg. This is 50/50 highway streets with the AC on most of the time. Compared to a couple weeks ago with the same driving and no AC I was getting 17.


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