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post #1 of (permalink) Old 09-05-2001, 04:15 PM Thread Starter
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Answer to Fuel Injection Test!

OK Gents… Here’s a test to see what you all have learned the last year or so on Fuel Injection[img]/wwwthreads_images/icons/smile.gif[/img]


1. Automatic Transmission swapped out.
2. Jeep was running and under it’s own power went up on ramps and shut off.
3. Transmission was swapped.

Jeep Ignition/fuel specifications:

1. GM HEI ignition.
2. Howell TBI Fuel Injection


1. No start condition.


1. No start….well Duh![img]/wwwthreads_images/icons/crazy.gif[/img]
2. Plugs firing.
3. On start up you can hear the fuel pump cycle 2 seconds and shut off.
4. The fuel pump is not noisy and sounds normal.


Part A. What do you do to diagnose the problem, list your steps?
Part B. What are you’re conclusions as to the problem?
Part C. How long should it take to find the problem?


1. I’ve lead you down the garden path, all the symptoms are correct… but not necessarily right.
2. The problem can be fixed without spending a dime.

The Answer will be given when the thread activity dies down or no one answers… which ever comes first. The The answer will be the steps I followed today to fix the problem.

Prize: None, you’re doing this for fame and glory!

<font color=red>****** Here's the Answer ******</font color=red>

Wow, you guys are good! You’re learning a lot! Years ago I sat down and formulated a set of a basic rules that I’ve used in modification and fabrication of my vehicles. I’ve used these rules as a guide and it’s not let me down. One of the rules is:

<font color=red>A modification, or fabrication, should not be so un-understandable that:
a. One needs to carry manuals to effect the repair.
b. The average backyard mechanic couldn’t figure it out.</font color=red>

When I first installed Fuel Injection I felt that I’d violated the rule (see 1.a above). Six years ago aftermarket fuel injection was expensive, a mystery, and just plain magic as there wasn’t a lot of books or information on the subject. I researched EFI for a year before committing buying a Howell TBI.

After the install I found out I couldn’t be more wrong. EFI is somewhat simple if you learn the basic parts and what each does and the difference between Open loop and Closed Loop operation. It just boils down to logic and troubleshooting skills that each of you has demonstrated so well in diagnosing this problem. Remember each of you is shooting in the dark, you’re not in front of the Jeep so you can only diagnose with the information I gave you. Sometimes that’s just not enough information. I have every confidence each of you who replied would have found the problem right-off.

So on to the fix:

1. Drop back to basics:
a. The TBI is in Open Loop when below about 140* coolant temp, so many of the EFI sensors can’t be blamed for the no-start condition. There are only two sensors involved in Open Loop, the Coolant Temp and the TPS
b. Ground the diagnostic terminal and obtain a 12 code and no others. This confirms the fact that the TBI, sensors and Computer are is working. 12 is an easy number to remember!
2. So then it’s a matter of Air, Fuel, and Timing,
3. The timing had not been disturbed, so it was ruled out, and confirmed the plug had a spark.
4. The TBI gets lots of air, so the problem must be fuel related.
5. The Electric Fuel pump was cycling in Run mode. That is, it turns on for 2 sec and pressurizes the fuel line, then turns off.
6. On start the engine cranks and there is no fuel from the injectors. This was confirmed by tearing a small piece of cardboard and placing it under the injector to see if a spray did occur…. That’s a back up to smelling the raw gas.

Humm…. No gas! But the fuel pump’s cycling? Am I being led down the garden path?

7. Unhook the fuel supply line and cycle the fuel pump.
8. No fuel is emitted during the cycle time. This is curious…. I heard the fuel pump cycle.
9. Remove the fuel pump from its protective PVC canister.
10. Pour gas in a jar on the front passenger’s fender.
11. Connect the fuel pump to the battery… it runs and sounds fine.
12. Attempt to siphon from the jar of gas.
13. Nothing… not even a drop is pumped.
14. Go get the half-used bottle of SeaFoam and pour it in a jar.
15. Siphon the SeaFoam into the fuel pump.
16. Nothing… nadda, zippo, zilch, zero… narry a drop emitted.
17. Continue to let the pump run…. But not too long as an electric fuel pump is cooled by the flow.
18. All of a sudden I hear a “pop” (That’s with ONE “o” folks) and SeaFoam is shooting everywhere out of the pump.
19. Re-insert the siphon into the jar of Gas.
20. Re-connect the pump and pump Gas 4 feet out into the driveway. That was exciting!
21. Reinstall the fuel pump into the PVC Canister.
22. Reconnect the fuel pump lines.
23. Start the Jeep.
24. It started just fine!


The fuel pump had so much varnish in it that it just plain couldn’t function and the outlet was blocked. The fuel treatment SeaFoam had emulsified the blockage and the “pop” that was heard was the blockage being shot out at fuel pump pressure.

<font color=red>Hint to self… never look at the fuel pump straight on when it’s running… it may be loaded… remember the sucking on the sand blaster tube?….</font color=red>

Time to diagnose the repair:

8 minutes

Time to effect the repair:

35 minutes

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