Stumble/backfire under load after installing Howell TBI

[jbenguerel]

I have the high flow filter that came with the kit. The kit was on my brother in laws '77 before mine so I can't speak for the debris in the pump. At this point it just stopped pumping all together. Went so far as to disconnect the fuel line from the tb and put it in a bucket to see if it wud pump fuel. Nothing....

[jbenguerel]

It backfires through the exhaust. It really is more of a miss or hesitation. The mechanic friends who have heard it call it a backfire but they are short repeated pops at high rpms.Do you think that the lack of fuel pressure could cause the injectors to pulse when they spray at high rpm? I haven't gotten to checking pressure b/c the pump stopped all together. Should have a new pump by Wednesday. Just keeping my fingers crossed that it was just a symptom of the pump dying and it'll be all better with the new pump. Lol

[chef]

It backfires through the exhaust. It really is more of a miss or hesitation. The mechanic friends who have heard it call it a backfire but they are short repeated pops at high rpms.Do you think that the lack of fuel pressure could cause the injectors to pulse when they spray at high rpm? I haven't gotten to checking pressure b/c the pump stopped all together. Should have a new pump by Wednesday. Just keeping my fingers crossed that it was just a symptom of the pump dying and it'll be all better with the new pump. Lol

Yes the lack of fuel would cause the injectors to pulse

[FSJ Guy]

What pump came with the kit? They used to use the E2000 (or similar) pump. AFAIK, it is not designed to be opened up by the end-user.

[jbenguerel]

Okay so after dealing my wife's car dying for a week and the jeep parts coming late too late to make my niagra rim trip, I got the new fuel pump installed and still have the same problem. Didn't even get better. I don't think that the fuel pressure is the issue but will buy a gauge tomorrow and check. I'm starting to wonder if it is the Tach pulse as previously suggested...

[FSJ Guy]

One other "trick" I read that you can do. Hook up your timing light to the COIL wire. Either at night or in your garage, shine the timing light at the TBI injectors (with the air cleaner off, of course!) and the strobe of the timing light will "freeze" the injector spray patter so you can see it easier.

Another think to think about would be the distributor pickup. But I don't see why it would fail only at high RPMs.

Can you datalog?

[jbenguerel]

With the Tach and fuel pressure gauge hooked up it cuts out at exactly 3500 rpm and there is no change to the fuel pressure which stays steady at 17psi.

The spray doesn't stop completely, it pulses.

I don't have the ability to data log. Very low tech garage. Lol

[FSJ Guy]

Are you running an MSD ignition box? The reason I ask is that some of them have rev limiters. But they usually will make the engine feel like it's stumbling instead of making it backfire.

When you say the spray doesn't completely stop, but instead pulses, does the spray appear to pulse BELOW 3,500 rpm?

[jbenguerel]

I'm running an msd coil. So no rev limiter that I know of unless it is in Howell's computer. It pulses only when it hits 3500 and starts to sputter

[FSJ Guy]

Can you swap to another ECM?

AFAIK, there is no rev limiter function with the 1227747 ECM's.

Have you called Howell about this? Maybe it is a known issue. <shrug>

[chef]

I'm running an msd coil. So no rev limiter that I know of unless it is in Howell's computer. It pulses only when it hits 3500 and starts to sputter

Does it do the same thing under load as sitting in park?

[jbenguerel]

I cud throw the stock coil in.

Yeah it does the same thing in park and driving.

[FSJ Guy]

If you have a spare coil, try that. It's free and would eliminate another variable.

[jbenguerel]

I must've dumped the stock coil. I could swear that I kept it but I must've been a fool and thrown it away at some point over the last year. BUT I did use my brain today and realize that I could easily put a video on youtube so that everyone could see the spray pattern. I checked my grounds and connections this morning. No change except that it is cutting out at 3300 rpm...as opposed to the 3500 the other day. Here is the video link

http://www.youtube.com/watch?v=THmH_XuTzuU

[FSJ Guy]

Time to call Howell?